The Ram's Eye - A Driver's Blog

Saturday, 5 November 2016

2016 Focus RS vs 2016 Mustang Shelby GT350R - Track Video

While testing a 2016 Focus RS for the comparison test, I caught up to a 2016 Mustang Shelby GT350R and had a friendly head-to-head battle. Both cars were completely stock. The video doesn't capture just how good that car sounds. We had a chat afterwords and the owner was very cool about it. His rear tires were starting to look old and he told me it felt a little less grippy than he was used to, so they could have been heat cycled out. Our track is also short and technical, so high hp cars don't get much room to stretch their legs, robbing them of some of the advantage they'd have at a power and/or longer track. Check out the video below for a couple of laps.

Wednesday, 2 November 2016

Ford Focus RS vs Subaru WRX STI vs Mitsubishi Evo X MR

All these cars have one common Achilles' heel. The engines sit entirely ahead of the front axles; a great family recipe for understeer. Then tell the front tires - already taxed from trying to keep that front engine sitting outside the wheelbase from going straight - to put some power down and you can only make matters worse. There are ways to mitigate the understeer with suspension tuning, of course, but the toughest part is power-on understeer. I don't want to get much into tires, but the thing to remember is that because tires have a certain "grip budget" - how much total grip they can hold/generate before they let go - when you get on the power in a car that sends power to the front wheels (FWD or AWD), you will rob some of the precious grip you were relying on to turn the car in order to put all or some power down. You'll run out of front lateral grip sooner than you would have otherwise, as a result. Worse yet, because of the unideal engine placement, you need every last bit of lateral grip in the front. So what you typically do to mitigate that understeer is, generally speaking, give the front tires far more grip than the rears.

You know what all good handling front end heavy, FWD cars have in common? They turn into tripods and kick up the inside rear wheel when turning. You need as much grip at the front as possible to keep that engine hanging in the front in check so you tune for weight transfer to the front, lightening up the rear end in the process. That's great in a FWD car but with AWD, you make the rears less effective - the same tires you're now trying to send power to.. after having just added a whole lot of effort, weight, complexity, and cost to the car in order to be able to utilize them. As a result, you can’t let these cars turn into tripods and pretend the inside wheel doesn't exist half way around a turn. You are now using the rear wheels for power so they are far more useful, for one. For another, you can afford to lose a little grip from the fronts to the rears, since they don’t have to transfer all the power anymore. You can never lose sight of the unideal engine placement, though, that demands a lot of grip in the front.

Why is all of this relevant? Because you need to spend just as much effort managing power as you do managing available grip by tuning the suspension. That's how each car defines itself. Where their characters and attitudes come from. And because differentials are a big factor in this, I made another post recently on various types of differentials in an effort to make this post more focused on the cars but still discuss diffs in a little more detail and answer some questions about the diffs discussed here. Here's a link to that post: Limited Slip Differentials - The Basics. With that said, let's start with the oldest car here; the Evo.

Mitsubishi Evo X MR

How many comparisons have thrown this out-of-production car into the mix of new entries to the segment? This isn't only out-of-production, it is also very old, with a platform that's a full generation and redesign older than the other cars here. You can notice that in NVH, the way the car looks, the way the interior feels.. but not the way the car drives.

Compared to the STI, the Evo X feels sharper, more nimble, and more agile. This is surprising because the STI, at first, seems to have the advantage. The Evo is heavier, to begin with. It's an older, presumably less stiff chassis. It uses a conventional bevel gear centre differential, giving it a 50:50 torque distribution. The STI's centre differential is a planetary type, giving Subaru the flexibility to gear it for a 41:59 torque distribution front to rear. To make matters worse, the Evo can bias torque to the front wheels by varying lockup in a clutch pack sending power to the rear. The STI can't (without slip and centre diff lock). The option of front power bias without the possibility of rear bias, more weight, and possibly softer chassis sound like a few strikes against the Evo. But the Evo is happy to return punches all day. 

Without slip, any power you send to the rear wheels will cause understeer. An open diff sends virtually equal torque to both wheels so there's no steering moment and your tractive forces push the car where the rear wheels are pointing; straight. A mechanical LSD sends more to the inside wheel around a turn until there is slip, so you even have a negative steering moment. What do you do? You CREATE steering moment! Enter torque vectoring differentials. The power you send to the back in the Evo goes through a torque vectoring differential to then distribute that power side to side - forcing it to the outside wheel creates steering moment. At the front, the Evo uses a gear-type LSD, maximizing use of available traction so you can put more power down. More power down at the front (without slip) is good, because the tractive forces are pointed in the direction you want to go, along with the front wheels. Both the Evo and the STI use limited slip mechanisms to lock front and rear axles if there is slip and shuffle more torque fore and aft. However, the centre diff in the Evo is strictly an electronic LSD. When going around a turn without slip, it is completely uncoupled. No lock, no resistance to turning. 

The final peace of the puzzle is power distribution. Why only 50% to the rears and why allow front bias? Well, you need a lot of grip in the front to keep the engine in check. If the car is turning, you need to allow weight transfer to the front to increase grip there because of the unideal engine placement. The downside is that you rob the rear wheels of their grip so they can't put down as much power as you'd like. Now, front power bias here is very different from what you hear people complain about in a performance car. That kind of power bias, typical in the tried-and-true Haldex AWD system, hurts because it is the default. You always get front power bias until there is slip, at which point the front tires are already struggling and the best you can do is ease their pain a little by lightening their load. In the Evo, power goes from the engine to the transmission, then to a differential that evenly distributes power front and rear. Then there is a clutch pack transferring power to the rear axle, which you can progressively disengage to put more power to the front if conditions allow (i.e. whenever you don't need peak lateral grip). So with that in mind, you either allow that (good) front power bias to be able to utilize more power there where you've put more of the available grip due to weight transfer, or you prevent a lot of weight transfer to the front so you can bias power to the back without losing traction, at the expense of front end grip and more neutral handling. The Evo chooses the former.

All of this translates into a huge difference on track. It turns in with surprising precision. You can still find some understeer at the limit but it is easy to avoid and manage. You can get heavy on the power very early and trust it. You need very little corrections and just let the car drive the proper line as if Mitsubishi taught it during development. I may be exaggerating but you'd probably be, too, if you've driven a few different cars on track and felt the difference. Another plus is that, because the Evo is this close to neutral, if the centre diff locks due to slip, it will help the car rotate. Because, if locked, the front and rear axles' speeds have to be closer than they would be, unlocked. That means the tires on one axle have to slip a little to more closely match the others. If you have more front end grip, the rears will slip first, helping the car rotate and reducing power-on understeer. But don't confuse that slip with lack of stability. The Evo wants to make a hero of you. It is so stable, so easy to control, that you'd be forgiven to think it can't go wrong. The whole car is focused on managing power as efficiently as possible - front to back and side to side - to optimize the turn. You can just feel the car working under power, managing the grip, managing the power distribution. And it feels so eager to do so.

Forget about lap times for a moment. They can easily be improved (to an extent) with some relatively minor tweaks. For example, when it first came out, this car did a lap of 3:13.3 at VIR for Car and Driver's LL 2008. That's only half a second ahead of the 3rd generation WRX STI, despite reviews generally agreeing that the Evo feels much sharper and track ready. It wasn't until they brought it back (in SE guise) for LL 2011 and did 3:10.5, putting it a little over 3 seconds ahead of the STI. And one way or another, it was still an Evo X. The times don't tell the whole story. Focusing on the times is missing the point. Despite the age, despite the crappy interior, the relative lack of refinement, the dire image of Mitsubishi, and even being out of production, this car feels just as sophisticated, track focused, and special as the other newer cars here. That's the point.

Subaru STI

I'm not sure if Subaru's reputation is what is influencing current design philosophy or current design philosophy is what's fueling the on-going reputation. But I imagine that at every design meeting during the STI's development, the head engineer always asked everyone involved: "so what have you done since the last meeting to make sure it better puts power down?" I can picture someone, at some point, suggested big rear anti roll bars during development for better turn in. He probably got fired. That's not to say the STI handles badly. It's still sharp with great turn in. It has a lot of grip and does not plow straight under power. That's just not its party piece. It's not its specialty. 

The STI claws the road under power. If it were an animal, it would be a big cat - a lion or a tiger - and every time you got on the power, it would crouch, wag its rear end sticking in the air, and pounce forward. Whereas the Evo is all about managing power, the STI is all about putting it down. Traction seems to be the priority. You need just a little more patience than the Evo before getting back on the power but then it will put power down with absolute tenacity.

It uses a gear type front diff like the Evo so there is no difference there. In the centre, though, it uses not one, but two types of limited slip mechanisms - a gear type and an electronically controlled clutch pack. The planetary gear centre diff utilizes helical gears to create thrust forces and provide some lockup under power. That means, as you roll into the power, the diff progressively locks. That’s great for traction as it locks before slip occurs (remember how the STI is all about traction?) but more lock means resistance to turning so it won’t be as agile. The second LSD is an electronically controlled clutch pack – similar to the Evo – to supplement the gear type for more locking if need be or if you want to manually select and lock the torque distribution instead of letting the computer do the work.

You can forget all of that torque vectoring non-sense in the Evo. That's what the STI would say if it could talk. In a slalom test by Edmunds back when the Evo X was introduced, they found that the torque vectoring diff can be caught off guard in short and quick transmissions like a tight slalom and wag the rear end a little. The STI wouldn't have any of that and would happily give up the effective steering from torque vectoring. The rear diff in the STI is another gear type differential, unlike torque vectoring in the Evo, which again locks under power. It won’t wait for slip or a computer to think and shuffle power. It doesn’t want to slip. That’s the STI’s mission.

Then you get to weight transfer, where the STI refuses to rob the rears of their traction, giving them better grip at the expense of the fronts. It's more stable and means you can put more power down without slip. But it's at the expense of some lateral grip at the front and that precise point-and-go attitude of the Evo. Corner speeds have to come down some, but you should be able to make up for it in traction in corner exit.

With that said, the STI has a certain charm to it - a certain mechanical feel that makes it more natural. It drives almost like a RWD car, but not the best and most sporty of the breed. It drives like a very tame one - one that is very capable but has safe understeer dialed in and massive amounts of traction. As is to be expected of the front weight bias, you get a good helping of limit understeer. If you go on the power, you can help the car rotate, but you do so by slip. Just as you would in a RWD car, especially if it's locked in 59% power going to the back. You can break traction and get it to rotate. It also uses brake-based lock, which does help, but isn't nearly as effective as a torque vectoring diff. The slip also feels abrupt compared to the Evo and the RS. That could have something to do with the modifications - this particular STI had camber (-2.5 degrees all around) and sticky BFGoodrich g-Force R1 track tires (which are different from the tires used by the owner for the lap time quoted at the end). The abruptness could easily be attributed to those near-slick track tires, but I would be surprised if, even when stock, the rear end would step out as smoothly as the Evo and or anywhere as gracefully as the RS.

The mechanical feel and nature does more to impress too, depending on how you look at it. The Evo will make a hero of you, but perhaps at the expense of doing more for you. You'll always wonder how much you could do without the car's help. In the STI, you feel more in control and will get it out feeling more accomplished, especially with the option of locking front to rear torque. It feels like the car just gave you all the traction in the world on a silver platter and what to do with it is up to you. The Evo has a wider range of torque distribution front to back and then again side to side on the rear axle. Aside from the torque vectoring diff simply sending torque to the outside wheel to help the car rotate, it's hard to say whether the Evo actually does that much more for you, as far as managing power, or the STI just hides it better. But it certainly feels like the STI is less intrusive or in control, which is a big plus in my book.

Ford Focus RS

If this car had any more hype and people talking about it, it'd have its own reality show. Drift mode, torque vectoring, optional Michelin Pilot Sport Cup 2 tires from the factory (standard in Canada), 350 hp, the lot. Plenty of buzzwords. Ford set it up for disappointment. It has to deliver on so many things, and deliver well, to meet expectations, let alone impress. It's bound to disappoint.. Or is it?

The RS takes the neutral balance of the Evo and turns it up a couple notches. It then takes the STI's rear power bias and turns that up a couple of notches as well. What's the problem in a front-end heavy FWD car, understeer? Ford says, with a smirk, let's fix that for you. When I said you could either allow front power and weight transfer bias or rear power and weight transfer bias, I actually left out secret option number 3. Give the front end a lot of grip, let the back lighten up, and still send plenty of power back there. Better still, allow the rear axle to use up to 100% of that power to one wheel to help the car steer. The RS has a very noble mission - make you forget it's a FWD-based hot hatch. And boy, does it ever try. You drive this car properly, and you may actually forget that you are driving a FWD-based hot hatch. The rotation under power is not only helpful, but very refreshing. And massively entertaining. Plus, you can't help but get all giddy when driving a humble Focus that power oversteers coming out of corners. The Evo makes use of an AWD system to beautifully manage power and maximize corner speed. The STI makes use of an AWD system to give you traction a 911 would envy. What Ford does, though, is use an AWD system to make the car turn. Speed seems like a byproduct since, you know, you do have to turn to get around a track. And the RS is very good at that.

The RS uses a torque vectoring rear differential like the Evo, although of completely different design that does not rely on a traditional differential at all. Instead, it uses two sets of hydraulically actuated wet clutch packs that individually control the amount of torque each rear wheel gets at all times. In the centre, the RS, once again, does away with a traditional differential and relies on those individual clutch packs to proportion power to the rear. If both clutches are disengaged, you get no transfer to the rear. If both clutches are equally locked - fully or partially - you get torque transfer in proportion to the amount of lock up, split equally between the two wheels. Or you could vary lockup between the two sides to individually send torque to either wheel. Using clutch packs to proportion power to the rear is very common in mainstream AWD vehicles, although is typically done via a clutch pack before the rear axle and a conventional rear differential. This is much less desirable than a differential in FWD-based performance cars, as discussed earlier. So how does the RS overcome this? It over speeds the rear wheels.

Similar to how the STI gears the centre diff to bias power to the back, the RS is geared at the power takeoff unit to drive the rear wheels faster, although much more aggressively at a ratio of 1.7 the speed of the fronts, thereby having a higher load and transferring more torque, resulting in rear bias. And, like the Evo, this also allows good front power bias if conditions allow by progressively reducing lockup on the clutch packs. At the front, the RS uses an open differential with brake-based lock, a disadvantage to the Evo and the STI. But, because of the aggressive front weight transfer, how much grip the the front axle has as a result, and how much power it sends to the back, I didn't run into the limitation of the front axle (i.e. excessive inside wheel slip). I have no doubt that you'd see an improvement with a true LSD at the front, but you'd probably struggle to get even near the same improvement that you'd see in a FWD car like the Focus ST.

Some people ran into overheating issues where the rear differential/drive unit (RDU) got disabled and the car basically became FWD. A friend of mine has an RS and ran into that problem the first day he was on the track. I never had a hiccup. That could be because of how little time I spent in the RS - a 15 minute sting, a 10 minute stint and a 5 minute stint. It could also be because of my driving style that we suspected strains the AWD system less (more on that in a moment). Or the fact that the car I drove was well broken in with over 12k kms on the clock, about 7.5k miles, because that same friend who ran into the issue the first time he was on track had no issues in subsequent times with more mileage. That lead us to thinking it might be an over protective feature during early break-in since the first time he was out, the car had just 1,800 kms on in, or just over 1,100 miles. I hope that we can say with more certainty with more track time next season whether or not that's an actual problem, but for now, it seems like a non issue.

So what does all of this mean on track? You'll have to recalibrate your turn in points and steering angles compared to a car with similar turn in response and handling balance because you simply don't need as much steering from the front wheels. You can feel the car working like the Evo but it doesn't seem "smart" in the sense of correcting your line. Where the Evo feels like it knows the right line and reads your mind, the RS doesn't. Yaw in the RS seems to be directly linked to your right foot - give more power and you get more rotation. If you are using a lot of steering and too much throttle, the car thinks you really want to turn and will put plenty of power outside to get the car turned hard, even if that means running out of the room on the inside and basically hitting an early apex. The Evo, I believe, knows exactly how hard the car should turn based on steering angle. If you're turning a certain amount and the yaw sensor says the car isn't turning enough, you have understeer, and it will shuffle power outside to turn the car. If yaw is too much, it will shuffle power inside to put the car back in line. The RS seems to have more faith in you, for better or for worse. The car gives you what you demand with your hands and right foot. Kind of like the way the STI gives you traction on a silver platter, only the RS gives you a hyper ability to turn

There are many excellent RWD cars that let you steer with your right foot. The difference is how much steering you can do and, let's not forget, that this is an AWD car. It still has a huge traction advantage. You can go flat out very early. In fact, in a lot of turns, I was flat out before apex because power no longer makes you go wide, it actually helps you turn. And you never have to worry about spinning out because it is massively easy to manage at the limit. It's fastest with some rear slip. The thing that you'll have to learn is trusting the car. Because it can hold and recover from huge yaw angles, all while still putting power down and gaining speed. You have to learn when to put your foot down and be able to put your foot down. Hard. That's the way you can maximize the AWD system. You need a lot of sisu or experience to do that, when your past experiences and your brain are telling you that you cannot do that here, otherwise you'll either spin out or plow straight.

It isn't without fault. The engine is still sitting far ahead and you can find limit understeer. But, compared to the other cars, it's like finding a lost sock in a dryer. The trick, in my opinion, is to not drive this car fast the way you do other cars. You don't maximize corner entry. In fact, you sacrifice corner entry just a little. The trouble is that, if you maximize corner entry, that means that you are coming in basically at the edge of grip. Right up to the limit. The car is as close to neutral as you'll probably get in an AWD hot hatch, but there's still some safe understeer left on the table. You'll find that and get frustrated. You can go on the power to correct, but because you're on the edge, you'll mostly correct by spinning, not by torque vectoring, because the tires are near the limit already in lateral grip and can't put much more power down without slipping. There's nothing wrong with that. That's what you do in a good RWD car to help the car rotate. But it's missing the point of this car and wasting all that went into the AWD system along with a good chunk of the torque vectoring benefits. You need to conserve some grip at the rear tires to use for putting power down because that power is going to help you turn.

The best part of all, I believe, is that you'll be just as fast if you suit your driving to the car. The same friend who bought an RS this summer complained about understeer in a few turns. He had better corner entry than me, with higher entry speed and later braking in nearly every corner on the track. His lap time? 0.28 s slower than mine. I could take much better advantage of torque vectoring because the rear tires weren't as burdened as they would have been with optimal entry. That means I can get the car rotated as I am on the power and gaining speed, giving me a better corner exit. I think throwing the car into a corner is good for fast turns. Conserve speed and momentum. In slow corners, though, you have to adjust your driving.

But no matter how you drive this car, the real treat is how close it is to absolute neutral handling. How easy it is to have fun with the power and how manageable and controllable it is when it lets go. It really does a very good impression of a true sports car, one that just happens to be a practical hatchback. And while it may fall short occasionally and let you know it isn't without compromise, it more than makes up for it by how much fun you'll have driving it.

VW Golf R

You might have noticed that the Golf R is curiously missing from the title. Or that the Evo X is in it, even though I previously posted and said that it is out (link: Mods and Update: Focus RS vs Golf R vs WRX STI vs Evo X). Initially, I was going to test all four cars (link to original post: Intro: Focus RS vs Golf R vs WRX STI vs Evo X). Some back and forth, scheduling conflicts, etc. meant that I could only get hot laps in the Focus RS, find out what the WRX STI and Evo X are like on track but no opportunity for a time, and no impressions at all in a Golf R. Such is the trouble without a big audience and manufacturer-provided cars for review.

I'm just as disappointed as you are. Due to the time of year, the season is coming to a close and I won't get another opportunity until the next season to test again so I thought I'd post what I have and hope for a better outcome next season

Lap Times 

Although I had no opportunity to do hot laps in the Evo and the STI, I got lap times and logs from the owners. First, here's a map of our local track, Atlantic Motorsport Park, to clarify a few turns. Namely, Turns 6, 8, and 10. All these turns don't need the use of brakes in entry or even backing off enough to scrub off speed. In fact, turn 6 is taken flat out from start to finish. As a result, they can't be marked well on the track logs so I hope the map below can clarify.

With that out of the way, here are the lap times, followed by track logs of the Evo vs the STI, Evo vs RS, and RS vs STI.

Best Lap
Evo X MR
- modifications:
  • Intercooler pipes
  • Cat-back exhaust
  • Cone air filter
  • Custom tune
  • --------------
  • Lowering springs
  • Rear anti-roll bar
  • --------------
  • 18x10 wheels
  • Firestone Firehawk Indy 500 tires sized 275/35/18
  • --------------
  • Carbotech track pads
  • Braided stainless steel brake lines
- modifications
  • -2.5 deg camber all around
  • Bridgestone Potenza RE-71R tires sized 265/40/18
Focus RS
- stock
  • Optional Michelin Sport Cup 2 tires (235/35/19)

STI vs Evo X: If they were stock and driven optimally by the same driver, you should expect higher corner speeds in the Evo but better exits in the STI. It's tough to say which car has the grip advantage as they stand, with modifications. The STI has stickier but slightly narrower rubber and very good camber for a street car but much narrower wheels. The Evo X has an AWD system more suited for maximizing corner speed, suspension upgrades, wider wheels and tires, but no camber and street tires. Their corner speeds are extremely close, suggesting it's wash if we assume comparable driver skills (remember, they're different drivers). The extra power in the Evo shows in steeper acceleration curves out of T2, T3, back straight, and T11 leading to the front straight and appears to have been the winning factor. Time wise, it looks like the Evo made all its lead on power, as they appear to be in a dead heat up to T5 leading to the back straight. The Evo should also have a slight advantage in shifting, being the MR with a dual clutch automated manual (it is quick).

Evo X & STI vs RS: Despite the stock suspension, much narrower wheels and tires, the RS appears to have a consistent advantage in corner speeds vs both cars through high speed turns - basically the second half of the track past turn 6 - presumably due to less understeer. The STI should have a huge grip advantage, with similarly sticky tires that are actually much wider and camber. The Evo is tougher to judge, since the RS has much better compound but both wheels and tires are a far narrower. I found that the Focus likes slightly slower-in-faster out approach in slow turns to utilize the torque vectoring, as I mentioned earlier, and this appears in the logs, where the Evo and STI have better corner entries into T2 and T3 but the RS seems to have better exits. 

The STI's modifications seem to provide it enough of a grip advantage to overcome the RS' handling advantage but without any more power, they're nearly tied. The Evo's suspension modifications seem to do the same, but the power advantage allows it to actually pull ahead slightly in just about every corner of the first half of the track. With that said, the RS was seriously held back by the 91 gas, IMO, since we don't have 93 locally.

It's clear, in my opinion, between T3 and T4 - just before braking point - the RS just loses steam and stops accelerating, then briefly gets back on. I could even feel that on the track. Between T4 and T5, the same thing happens. Then again between T5 and T6 and on the back straight. Finally, after exiting T11, the RS pulls power again before finishing on the front straight. How much is that worth? I went through the logs and adjusted the data as if the RS didn't lose power and here's the result:

Yep, just over a second. The lap time would have been 1:18.61, 1.01 s faster than otherwise. This is with absolutely no changes to the lap - same turn in, braking points, amount of braking, etc. - as you can see by the two laps being identical except for the sections where the RS seemed to have pulled power. How much is it making on 91? Don't know, but the Mustang EcoBoost is supposed to lose 35 hp when going from 93 to 87, 11.3% of peak. If we assume the same in the RS, it would be making 310 hp on 87 and somewhere between 310 and 350 on 91, which should actually be optimistic because the RS makes more boost so it should be more sensitive to octane than the Mustang. To calculate acceleration assuming no loss of power due to 91 gas, I used Car and Driver's test data of the RS, trended them, and used that data to calculate adjusted speeds had the car not pulled power. With the corrections, the lap times would look more like this:

Best Lap
Evo X MR      1:18.06
WRX STI1:19.72
Focus RS 1:18.61

Another disadvantage is seat time. Where best laps for the Evo and the STI were set by the owners, with hours of seat time in the cars, I had just under half an hour in the RS overall. The owners of both cars have had these cars for as long as I've known them, about two seasons. But even within one day, in a car you're already very familiar with, you can expect to get better as the day goes along (unless heat becomes a factor). Case in point; the 1:18 time in the Evo was preceded by slower lap times, where the first session was all 1:20's and slower, the second was 1:19's, and the third had the 1:18 lap. If we assume a similar drop in the RS with more seat time (~ 2 seconds), along with 93 gas or octane boost (another ~ 1 second), the RS would have the best lap by a substantial margin, with a best lap in the 1:16 range.

3rd Place: Subaru WRX STI: It was really tough between this and the Evo. Assuming all are stock, I think the STI would be the easiest to drive fast for an average track guy who goes to a couple track days and HPDS's a year. It has the most traction so it puts power down really well and, because it would make most of the time in corner exit, you can still get a great lap even if you don't nail the braking and corner entry. The RS and Evo need you to work more on those areas. It is also the most natural feeling in terms of handling and it's the one I would put my money on when the white stuff starts falling. But on track, compared to the other two, it feels like it's missing an edge.

2nd Place: Mitsubishi Evo X MR: I still cannot get over how this car drives on track despite its age. It is hugely impressive. It had the best raw time. It feels so precise, yet so stable, and manages power really well. For someone who doesn't car about the added practicality of the hatch, the refinement, or the subjective fun to drive factor of the RS, the Evo would probably be a more appealing car.

1st Place: Ford Focus RS: If one of these cars would serve as a daily driver, you'd never regret picking this car just because of how much more refined it is, plus the practicality of a hatchback. And then you'd take it to a track and find out what a blast it is. It is more neutral than any other production hot hatch dares to be. It will powerslide and dance, at full throttle, with just the right amount of yaw in corner exit, in a way a FWD-based car has no right to. And, if you consider the modifications of the other cars, the lack of 93 gas and octane boost during the test, and the very limited seat time, you'll find the raw and adjusted lap times to be very impressive. Did I mention it's easily the most fun?

I've put a lot of time researching the AWD systems of these cars, especially the Evo X and the STI, since it seems no two people quite agree on exactly how they work. I cannot say with 100% certainty that I interpreted the countless articles, diagrams, and drivetrain sections properly, so take that for what it's worth. There are a lot of conflicting opinions out there and you may have done your own research and come up with your own understanding that's different. If that's the case, feel free to comment or message me and include links/source and I'll be happy to update if there's an error. 

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Photography by Kevin Doubleday and Albert Hofman

Monday, 24 October 2016

2017 Camaro ZL1 Beats Previous Generation’s Nürburgring Lap Time

The new 2017 +Chevrolet Camaro ZL1, expected in showrooms by the end of this year, just beat the benchmark set by the last generation ZL1. With a lap time of 7:29.60, it is 11.67 faster faster than the last generation and even beat the last generation Z/28's time of 7:37.9 - which was done on Pirelli P Zero Trofeo R tires, far grippier than the Eagle F1 Supercar used on the ZL1. The car used is unchanged from the one you'll be able to buy, aside from the installation of data acquisition equipment, a roll hoop, and Sparco racing seats with six-point harnesses. Otherwise, the car was production stock and included the following:

  • 6.2-liter supercharged LT4 V-8 making 650 horsepower and 650 lb-ft of torque
  • All-new 10R90 10-speed automatic transmission (set to Track mode to enable Performance Algorithm Shift calibration, providing optimal gear selection without the need to manually select gears)
  • FE4 Suspension with Magnetic Ride Control
  • Performance Traction Management
  • Forged 20-inch wheels with Goodyear Eagle F1 Supercar 3 tires
  • Brembo brakes with front 15.4-inch rotors and six-piston calipers and rear 14.4-inch rotors and four-piston calipers
  • Lift-reducing front fascia elements with cooling ducts and Chevrolet “flowtie”
  • Full underbody shielding
  • ZL1-specific rear spoiler and diffuser
  • 11 heat exchanger

And best of all, with the exception of the 10 speed auto, all the above is included as standard, with no requirement to purchase additional performance packages. On a track like the 'Ring, the auto would have been worth a few seconds, I figure, with the number of shifts required so if you get it with the manual, you might close the gap compared to the last gen Z/28, but the time is still phenomenal and runs with plenty of very capable cars. A lot of times aren't official on Wikipedia or Fastest Laps aren't manufacturer official so they're hard to compare, but a notable victim is an AMG-confirmed lap time of lap time of 7:30.0 for a 2013 SLS AMG GT.  Plus, beating the mighty 5th gen Z/28 by over 8 seconds is quite a feat, since we've seen that Z/28 beat cars like the GT-R, 991 Turbo S, and Mercedes-AMG GT S when tested by Motor Trend or Car and Driver. This should be one heck of a tough car to beat on track. I can't wait to see how it does in a comparison test. Until then, here's a video of the lap:

Saturday, 22 October 2016

Limited Slip Differentials - The Basics

I'm finishing up a comparison post (link to introduction: Intro: Focus RS vs Golf R vs WRX STI vs Evo X) and, throughout the post, I realized that I have to go off topic a lot to talk about how each type of differential changes the way the car drives. As a result, I thought I'd write a separate post to go into more detail before I post the other one to keep the other more focused on the cars and avoid veering off topic too much.

By saying "Limited Slip Differentials" in the title, I am including torque vectoring diffs because, although current conventional terminology treats them differently, a torque vectoring differential is, in essence, a very sophisticated limited slip diff (LSD) that can be manipulated to actively help the car handle better. And while non of the cars in the comparison use open (without help from the brakes) or non-gear mechanical LSD’s, I’ll briefly discuss them so that the post is more inclusive. I’ll only focus on using power to help the handling or how a diff can handicap that, since the reason I started to write this post is to demonstrate how the differentials help each car. I won’t talk about other techniques that could help you manage a car’s weaknesses, such as changing turn in points, apexes, trailbraking, etc.

So how do traditional LSD's and torque vectoring diffs (TVD) help the car? Let's first start with open differentials.

Open Differentials

These are the most common differentials and they are the best at being differentials. The differential's job is to allow two wheels on the same axle to spin at different speeds so a car could smoothly go around a corner since each wheel has to travel a different path and, therefore, at a different speed - hence the name - to reach the end point of the turn at the same time. The video below has been used countless times to demonstrate how a diff works and, although made by GM almost 80 years ago, is still one of the best videos I've found that explains very simply and visually how a differential works (fast forward to about 2:00 in).

I don't want to get into the internals and workings of a differential, but I wanted to share that video because understanding the basics will help with understanding the impacts of various types of differentials. As you can see in the video, an open diff allows one wheel to spin endlessly, even if the other is completely stationary. The demonstration at 5:30 into the video shows that. If one wheel has a lot of traction, it's harder to spin, much like being held still in the video relative to the other one, (the road is "holding" the tire, in effect). If the other has little traction for some reason, the diff will spin it, since it is easier to spin. The diff transfers virtually equal amounts of torque to both wheels so the wheel with little traction will dictate how much torque the wheel with a lot of traction gets because if you give more torque than the low traction wheel can hold, it will spin, reducing your traction even more as well as lateral grip.

This is a double whammy if you have uneven available grip between two wheels on the same axle. When you have one wheel that has relatively little torque carrying capacity, but no way to unevenly distribute torque, you can more easily overpower it. Moreover, the wheel with a lot of traction and, therefore, good torque carrying/transfer capacity is underutilized. The result is limiting how much power you can use to move (accelerate) and increased likelihood of reducing your grip by spinning the low-grip wheel, which still contributes to the car's overall lateral and forward grip available. If that happens at the rear axle (RWD), that spinning low-traction wheel means less grip at the rear end and more likely to oversteer. On the front axle, it's understeer. This is assuming that, in either scenario, you're applying power.

How does this work on track? When you're going around a turn, the inside wheel is unloaded because weight is transferred to the outside wheel, which means the inside wheel has less grip. That means it can transfer less torque than the outside and if you exceed that, it will spin. If it starts to spin (excessively), it will have even less grip. Less grip means you'll be able to use even less power and your corner speed has to come down since one of the tires now has less grip. In short, an open diff works really well at allowing different speeds between the two wheels but limits how much you power you can put down and makes it easier to spin under power.

So what does that mean if you're pushing the car? When approaching a turn, as you start to turn in, you come off the power. Typically.. The reason I say typically is that with some of the other differentials, you can actually start using more than maintenance throttle as soon as you come off the brakes, but more on that later. For an open diff, you are off, aside from maintenance throttle. If you can add power and gain speed between turn in and apex (where you start to unwind), you lost more speed than you needed on the brakes. Assuming optimal entry, you shouldn’t be able to add speed without understeer, oversteer, or a neutral drift, depending on the balance of the car. The diff can’t help you here. Worse yet, on a FWD car, you can’t use the power to help the car rotate. Unlike RWD, where you could judiciously overpower the rear wheels, inducing slip and rotating the car that way, if you overpower the driven wheels in a FWD car, there’s no way to go but straight. And this is very easy to do in an open diff while going around a turn, with the inside wheel being unloaded.

Need more bad news? The vast majority of FWD cars have a transverse engine layout, placing the engine far outside the wheelbase of the car. The Dodge and Chrysler Intrepid come to mind as exceptions, with longitudinal engine, FWD layout. Audi A4s, too, if you don't get the AWD option. But even those still put the engine basically entirely in front of the front axle. This generates very nasty forces and moments that do their best at pulling the car straight when you want to turn. Then, of course, you have typical OEM suspension tuning that favours the front end letting go before the rear end for safe limit-understeer. The result is frustration and anger, perhaps some cursing, and eventually vowing against open differentials on the track and maybe even FWD all together (which can actually be made to work very well on a track).

Limited Slip Differentials

There are many types of limited slip differentials and, like I mentioned, I won't get into how they operate, just how they affect the car. I'm referring strictly to mechanical, non-gear type limited slip differentials here. These differentials are typically open differentials at heart with modifications or additions. Those modifications are designed to resist a speed variance across the differential. The result is a limit to how much faster a wheel can spin relative to the other, overcoming the limitations I mentioned for an open diff. This is achieved by locking the two axles together (to an extent). That extent depends on the design and spec of the differential - typically referred to in a percentage (%) number and occasionally as a Torque Bias Ratio (TBR). That % number is the difference in torque (in % of total) the diff can provide between the two axles. TBR is the ratio between the torque sent to the outside wheel to the inside wheel that the diff can deliver. The higher either number, the better the diff will be at putting power down as it allows more lock up. But higher isn't always better.

Limiting slip of a low traction wheel is great, as it can be the difference between accelerating and backing off the power when exiting a turn on a track. Trouble is, when under power, a limited slip diff of this type can't differentiate between turning and a slipping wheel. If you're going around a turn and starting to feed in power, the outside wheel is spinning faster than the inside wheel, which is normal. But the diff will start to lock up, in response to the speed differential, thereby transfering torque to the inside wheel. That means the unloaded wheel gets more torque, the opposite of what you want, and generates a steering moment in the opposite direction of the turn. Moreover, by locking up, there is resistance to the wheels spinning at different speeds, which is resistance to turning (i.e. understeer) since that requires each wheel travels a different arc at a different speed around a turn.

So how do these help, considering all that? You can go faster by using more power earlier in corner exit and, due to limiting inside wheel spin, you won't lose traction as easily which means you can better maintain your available grip. The downside is understeer on a RWD car. This is introduced by three factors:

- Locking up to any degree provides less speed differentiation than no lock up at all, which we've established is required for the car to turn.

- Putting more power down means more weight transfer to the rear end, which results in less grip at the front end; more understeer.

- You can maintain your grip for longer due to no inside wheel spin. If the rear axle can hold on for longer, you'll increase understeer.

- Torque transfer to inside rear wheel in a turn prior to it slipping generates negative steering moment (in opposite direction to the turn), resulting in understeer.

With that said, a car without a LSD will be slower than one with because, even if your corner speeds come down a little, you can get back on the power much sooner and more aggressively and that's where you make most of your time. Moreover, you can tune the suspension and chassis to reduce understeer so you typically only notice the understeer on a car that had a LSD added but is otherwise unchanged. And most good summer/track tires generate their highest grip with a very small amount of slip, meaning that if you're aggressive with the throttle, enough to just barely overpower the inside wheel where the diff is working as intended, that very small amount of slip is not hurting you and now the inside wheel is beginning to slip, causing lockup and torque transfer to the outside. As a result, you'll find that most good handling RWD cars actually have LSD's, such as modern Camaros and Mustangs, Corvettes, BMW's, Subaru BRZ/Toyota 86, etc. 

It gets even better on a FWD car, since you only have the first two factors against you. The other two are actually helping you; more grip at the front is less understeer and torque delivered by either front tire generates positive steering moment.  That means a LSD typically curbs understeer on a FWD car, even with all else being the same. The one caveat is that the axle locking can make it difficult to steer, if aggressive.

Torque sensing or gear type differentials

Torsen and Quaife are probably the most common of these types of differentials. They are very similar in function to more common LSDs discussed above, except rely on gears configured in a way to bind and provide locking. A gear type LSD is torque sensitive, hence the name Torsen (Tor for Torque and sen for Sensing). Torsen has two major designs T1 (first gen) and T2 (shown above). T2's are very similar to Quaife design (main picture above introduction). They all operate based on friction between the gears and the differential casing. Due to the inherent angle of the teeth on a helical gear, transmitting torque from gear to gear also generates thrust forces. These forces pushes the "pinion" helical gears against the differential case, providing lockup, instead of using a clutch pack to lock the axles to the case, for instance. The great thing about them is that they transfer torque even before slip occurs, since they progressively lock up as gear thrust forces increase and these forces are proportional to torque transferred by the diff and independent of speed differential across axles. In other words, as you apply more power, the diff progressively locks up and its capacity to carry torque increases, regardless of whether one of the wheels has begun to slip or not.

Both Torsen generations, T1 and T2, use the same basic principle but T1's are very rarely used now in new applications, if at all, and they rely on a different design that increases lock up. They utilize two different types of gears (helical and worm). Inherent to the design and arrangement of gears, the gears will progressively bind as speed difference between the wheels increases when there is excessive or uneven slip. Due to this nature, T1 LSD's typically have very high TBR's and provide a lot of lock-up.

The downside to gear type differentials is that they typically can't take as much abuse. They don't like to be launched hard and high hp, high grip cars seem to have issues with them since they operate on the principal of binding gears and diff cases. With that said, they are low maintenance and last longer in more forgiving cars. That's not necessarily slow, pedestrian cars - the list of high hp, high performance cars that includes them as OEM diffs includes 5th gen Camaro Z/28, the '12-13 Mustang Boss 302's, and the current Shelby GT350's, all of which utilize the T2 generation.

So how do these differ from the more conventional LSD's in operation? The main difference is how it locks. As discussed earlier, they lock because of the helical gears generating thrust forces that push the gears against the diff case, effectively binding and locking it up. Since the force generated is proportional to the force (torque) being transferred by the gears, lock up is proportional to input power (i.e. how much power you're applying). If you're off the gas, it's basically an open differential. As you roll into the power, it progressively and smoothly locks up. The benefit to that is, because lock up is smoother and the diff is more open off power, you can typically get away with higher torque bias ratios than non gear LSD's at maximum lockup without seeing as much of the side effects of higher locking. The higher TBR allows better traction performance.

Moreover, the fact that lock up is proportional to input power means the diff locks up as you send more power, without the need for slip. Non-gear LSD's need slip to work as intended. If you are going around a turn with no inside wheel slip at all, the outside wheel is traveling faster and the traditional LSD is locking up, slowing it down and speeding up the inside wheel, therefore, transferring more torque to the inside wheel. As you increase power, the inside wheel begins to slip and only as its speed passes the outside does the diff begin to slow it down. In other words, the inside wheel must slip first and then be limited. The diff will go through the sequence of little lock up (outside wheel faster than inside), then no lock up (inside wheel beginning to get over powered, spin, and accelerate to match outside, which from the diffs perspective is like the car going straight), then lock up again as the inside wheel speed starts to exceed outside. In a Torsen, the inside wheel is limited before it slips, since lock up happens before slip. Subtle differences, but can change how the car feels, plus the higher TBR means cars can better put power down, accelerate faster out of turns, and generally perform better on track.

Brake-based Differential Lock

A car that uses brake-based limit slip action utilizes an open differential just like described above but attempts to solve the shortcomings by applying the brakes to individual wheels. If you go on the power and one wheel spins, the car realizes that and applies the brakes at the spinning wheel. From the differential's perspective, that wheel now is harder to turn and more torque will get transferred to it. Fortunately, just as much torque will get transferred to the wheel with grip, giving better traction performance.

In high performance driving, this solves the two shortcomings of an open differential, loss of grip due to a spinning wheel and under utilizing good grip at the loaded, outside tire. As we've established, an open diff transfers equal torque to both wheels. In order to distribute torque where you want it (unevenly), the brakes are engaged to slow down the one wheel spinning excessively. It is artificially creating resistance at the low traction wheel (i.e. the brakes "grip" the wheel instead of the road through the tire). This increases the torque holding capacity of that wheel, and the diff as a whole, thereby allowing the diff to transfer more torque overall, half of which goes to the outside wheel where it can all be used. The downside is wasting some power simply spinning the low traction wheel against the brakes. The second problem is, as a result of trying to power the low traction wheel against the brakes, the brakes can over heat and prematurely wear.

What's it like to drive? The tech is extremely flexible because it provides complete uncoupling and independence between the two wheels when no lock up is needed and infinitely variable and adjustable bias when you do. You have non of the shortcomings of mechanical LSD's. But you'll hear a lot of owners and reviewers complain about their effectiveness, or lack thereof. The problem is the application, not the tech. In a Focus ST or a Golf GTI (non PP), you don't have liberally sized brakes, brake cooling, brake system capacity, etc. In reality, an optimized brake based set up can work very well. McLaren uses them, for example. You won't hear too many people complain about their performance.

When you already have massive braking thermal capacity, cooling air flow, braking power, etc, you could rely on this system and avoid a similarly flexible torque vectoring system. That would not only save cost and complexity since all you're adding is the programming to control the brakes the car already has, it also saves weight since a torque vectoring differential can be heavy. The one Lexus uses on the RC F and GS F, for instance, adds almost 70 lbs compared to the standard Torsen differential offered, itself a heavier system than open differentials. But brake-based lockup does have issues, otherwise, on non optimal cars - think non mid-engine, cost constrained, limited in space, or just about every other car that us mere mortals can buy.. And you waste the engine's power spinning the inside wheel.

To put that into perspective, my car has a Torsen diff with a bias ratio of 2.7 - meaning it can allow the outside wheel to get 2.7 times the amount of torque the inside wheel has while remaining locked up (which is equivalent to a 46% clutch type LSD, if you're curios). My car has 380 lb-ft of torque. That means, in an ideal traction scenario, at peak torque and lockup, going WOT, the engine is sending 380 lb-ft of torque to the diff and the diff is transferring all of it - 103 lb-ft will go to the inside wheel and 277 lb-ft will go to the outside - a difference of 174 lb-ft. To achieve the same bias with brake lock, each axle has to get the same amount of torque - the difference is that some will be used to spin the brakes. How much? 50% of the difference goes to the brakes or 87 lb-ft.  That translates to 75 hp (at 4,500 rpm where peak torque occurs), in effect turning my car down from a 444 hp car to a 369 hp car. Bad.. very bad. Moreover, those 75 hp have to be transferred into heat by the brakes and once those brakes overheat, they back off and you approach an open differential. This extent of power loss would be rare and if it were to happen, wouldn't last long, but it demonstrates how bad it can be. In a mid-engine car like a McLaren, where you have gobs of traction due to rear weight and optimal suspension tuning, you may not need as aggressive a torque bias and you have brakes the size of the moon that can handle the heat. But in every day cars, it doesn't work very well. Not yet anyway.


eLSD is typically used as short for electronic limited slip differentials. They basically combine the benefits of all the above without any of the downsides. It can take more abuse than a gear type. It can lock up smoothly like a gear type. It doesn't have the same resistance to speed differentiation (unless activated) so it can have a higher lock-up with no downside. It is electronically controlled so it can selectively lock and unlock as needed based on real time calculations and inputs from various sensors. It doesn't have to worry about brakes overheating. Its only downside, really, is complexity.

Unlike a mechanical LSD, it can distinguish between a faster spinning outside wheel as you turn (with no slip) and a faster spinning inside wheel due to slip. It won't lockup unless slip is happening, eliminating the negative moment due to torque sent to the inside rear wheel before slip occurs - what mechanical LSD will do. It can give you high lock when you need, say, exiting a slow narrow turn, and low lock around a fast sweeper, reducing understeer you'd get with a high lock. In summary, it gives you higher traction performance while reducing understeer when you don't need lockup.

Torque Vectoring Differential

A torque vectoring differential is very similar to an eLSD. The main difference is that eLSD's only transfer torque from slower to faster. An eLSD is a basically a typical LSD, say a clutch-type, where the clutches, and therefore amount of lockup, are electronically controlled instead of passively based on the difference in speed between the two wheels on an axle. That means that they can control when and how much to lock up but after that, the same principles apply and torque is biased from the faster spinning wheel to the slower wheel. However, a torque vectoring diff can transfer torque either way and can do so independently of a speed differential. The benefit is better control (from the car) and wider range of adjustability, allowing the car to correct and/or improve more frequently. Moreover, a torque vectoring differential typically doesn't transfer torque by locking up. Instead, it utilizes actuators (clutches and/or motors) and gear sets to overdrive or under-drive each wheel independently.

What does this mean? It means you have no resistance to speed differentiation (i.e. understeer) but as much torque transfer to either wheel (can be up to 100% of torque sent to the diff) as you want. The downside of lockup (understeer) is eliminated, a huge plus to start with. Then you get the best torque bias (basically infinite if designed to allow 100%) you could get, allowing you to utilize every last bit of traction available, and to top it off, you can have individual wheel torque control to help the car handle. For example, if the back end is coming out, you could vector torque to the inside to bring it in. This has the same effect as a stability control system applying individual braking to a wheel or more to bring the car back in shape but braking means scrubbing off speed. Torque vectoring doesn't. You could also transfer torque to the outside wheel to help the car rotate if the car is understeering, without forcing lock up. It's a technically wonderful system. The range of adjustments is huge. Opportunities to improve the handling are plentiful. It can make a huge difference in how the car handles. The only downsides, really, are even more complexity and a less "mechanical" feel.


Which one is best? Well, brake-based systems are hugely variable and I'd only take one if I had to choose between one and an open diff. Otherwise, my preference is the gear type LSDs, even though they aren't as capable as electronic controlled ones. They provide the best performance without going to an electronically controlled system. Compared to electronically controlled ones, they're more natural feeling, simpler, and cheaper to maintain. They demand more of you, expect less of the car. But the same can be said for better tires, better shocks, stiffer chassis, etc. so I can see arguing both ways. I would imagine that someone learning on and sticking to torque vectoring tech on track would see it as natural and consider it a baseline, anything else is a compromise. That wasn't the case for me, so they will always seem like the deviation from norm - the cool tech that manipulates the car to your advantage, not the bare essentials.

With that said, in a FWD (never seen one) or FWD-based AWD car, I would absolutely and unquestionably give in and take torque vectoring and/or eLSD's. In a heart beat. The drivetrain layout is working very hard against you to prevent the car from doing what you want it to do. The tech does its best to mitigate the limitations. The way I see it: it almost undoes the crime that is FWD-based, transverse engine layout as opposed to improve the text book longitudinal front engine, RWD layout.

Friday, 30 September 2016

Chevrolet 1LE & Grand Sport - How do they do it? Part 1

Recently, Chevrolets seem to have been punching far above their weights and a lot of people (myself included) are impressed. Sure, Corvettes have always been formidable track cars, but they're low, light, purpose-built, and didn't blow expectations - just provided excellent value. Now, all +Chevrolet  track cars, especially Camaros, seem to be overreaching and, combined with excellent chassis tuning, have been doing wonders for GM's chassis engineers' image. I decided to take the time and do some research to try and figure out what GM is doing that others aren't (or can't). Before I start, I'd like to point out that this is based only on my own understanding and research, not an interview or publication by GM, so take that for what it's worth.

Since I haven't posted about the latest of Chevy's track-focused models/trim packages, I thought I'd first take this opportunity and talk about what you get. Whether you're looking at a Camaro V6, Camaro SS, or Corvette, choosing the 1LE package or Grand Sport will not bring extra power. Instead, those packages help you make the most of what's already available. You get no extra power but better track performance and longevity. Here's what you get, as best as I could find:

Camaro (V6) 1LE
- Functional front splitter (unique design to the V6)
- Functional rear spoiler (shared by V6 and SS)
- 245/40/20 front and 275/35/20 rear tires, mounted on forged wheels
- Oil cooler, bigger engine coolant capacity, and rear differential cooler
- Upgraded fuel pump and tank from the SS
- Upgraded dampers, rear sub-frame mounts, ball-jointed rear toe links, and anti roll bar, all taken from the standard SS
- Four piston front brembo calipers. Rears are unchanged, presumably one piston sliding calipers.
- Limited slip differential (standard on all V6 Camaros with the 6-speed manual)

Camaro SS 1LE
- Functional front splitter (unique design to the SS)
- Functional rear spoiler (shared by V6 and SS)
- 285/30/20 front and 305/20/20 rear tires, mounted on forged wheels
- SS already has oil cooler, bigger engine coolant capacity, rear diff cooler, plus transmission cooler so 1LE does not provide additional cooling capacity.
- Upgraded (magnetic) shocks and springs.
- Upgraded anti roll bars, rear toe links, rear trailing arms, and rear sub-frame mounts all taken from the ZL1
- Six piston front brembo calipers clamping on two piece, aluminum hat front rotors and four piston rear brembo calipers with one piece rotors
- Electronic limited slip differential (standard SS all get mechanical limited slip differentials).

Corvette Grand Sport
- The wide body of the Z06 (in other words, wide fenders to fit fat sticky tires) along with all cooling and aero ducts and passages
- 285/30/19 front and 335/25/20 rear tires, mounted on forged wheels
- Carbon ceramic brake rotors
- Upgraded aero package - the same spec as the stage 2 aero package on the Corvette Z06 (i.e. a Z06 with the Z07 package but not the Performance aero kit or stage 3). Stage 3 brings larger end plates to the front splitter and an adjustable, transparent wicker bill/gurney flap on the rear spoiler. Chevy determined that Stage 3 brings too much drag that isn't welcome without the additional thrust that the Z06 brings to the party.
- Dry sump oiling system (you can get with Z51 package)
- Dual mode exhaust with 460 hp (you can get with the Z51 package)
- Electronic limited slip differential (you can get with the Z51 package)
- Bigger brakes (you can get with the Z51 package)
- Upgraded springs, dampers, and anti-roll bars (you can get with the Z51 package, but the Grand Sport package then turns up the suspension stiffness a notch to sit nicely between the Z51 and Z06)
- Differential and transmission cooling (you can get with the Z51 package)
- Increased engine cooling capacity (you can get with the Z51 package)

So, in summary, all three cars provide downforce, or at least reduce lift for the Camaros (I haven't found data stating downforce numbers), additional cooling where necessary, more braking power, bigger tires, and stiffer suspension tuning. Additionally, except for the V6 Camaro, the cars can put more power down thanks to the electronic limited slip differentials. But what is special about Chevys? Every manufacturer addresses the same areas, if to different extents, but they can't seem to catch up.

The Corvette Grand Sport, for example, is only one tenth behind the GT3 RS, basically a dead heat at 2:47.1 for the Vette vs 2:47 flat for the Porsche, despite the Corvette having LESS power and weighing MORE. Consider this too: both use the same Michelin Pilot Sport Cup 2 tires, albeit tailored specifically for each car. The SS 1LE, at 2:54.8, is nearly tied with a Cayman GT4 (0.8 s behind), despite the GT4 being far lighter, enough to give it a superior power to weight ratio, and using even better tires - the same Pilot Sport Cup 2 vs the Camaro using Goodyear's equivalent to Michelin's Pilot Super Sport (that testing and reviews rate even lower than the Super Sport). How does Chevy do it?

Well, we can tell right off the bat that power isn't the answer. These Chevys are typically outright under-powered on raw numbers or at least power to weight ratio compared to cars they can beat or keep up with. Braking? Highly unlikely. Competitors use gigantic rotors and calipers that can (safely) be assumed to be sized properly with appropriate brake boosters and system pressure. Handling? Read a review of a Cayman GT4 or a 991 GT3 RS and tell me they're lacking. They're stable, yet neutral, handle road undulations, put power down well, etc. Could one be a little bit better than the other? Sure, but we aren't comparing a Corvette to a Beetle here. Plus, declaring them better means stating that Chevy can better design cars to handle than Porsche..

Aero? I hate making assumptions based on such superficial observations.. I really do. But I'll challenge you to this: take a gooood long look at the spoiler on the back of a Cayman GT4. Now look at the.. let's be kind and say relatively handicapped deck-lid spoiler on the trunk of a Camaro 1LE. Then tell yourself that the Camaro has more downforce than the GT4. Can you keep a straight face? I'm not saying that spoilers are the be all end all as far as downforce. There are many ways of managing air flow to change speed and create areas of relative low and high pressures to generate downforce. But it gets harder to do in a compromised car, such as the Camaro, where there are more space constraints than, say, a 2 seater mid-engine car like the Cayman. Plus, a spoiler, an airfoil one in particular, is a very effective way of generating aerodynamic forces. Planes use them (wings). Wind turbines use them (blades). You get the point.

On a side note, you should never underestimate the capability of deck lid or lip spoiler to generate downforce. While pedestal spoilers are far more common in racing, deck lid spoilers can still generate serious downforce. The one on the back of the Camaro 1LEs is simply not very large, the lip doesn't stand very tall, and angle of attack doesn't seem aggressive. Compare it to the last generation Z/28 for example. Here it is, below, with the optional wicker bill or Gurney flap, without which Randy Pobst in Motor Trend testing found the Camaro Z/28 loose and unstable, even though the spoiler alone has a much larger surface area and more aggressive angle of attack than the one on the current Camaro 1LE. So, without real test data, I am making a somewhat-educated guess that they don't have superior downforce.

A comparison of the Corvette Grand Sport vs 911 GT3 RS tells a similar story. Although, in this case, we actually do have numbers. The Corvette Z06 with the Z07 package and Performance Aero Kit (i.e. Stage 3 aero) produces 350 lbs of downforce at 150 mph, according to an article posted by Jalopnik about testing the Z06 at Spring Mountain Motorsports Park, being invited by Chevrolet (link: 2015 Corvette Z06: A 650 HP All-American Middle Finger To Euro Supercars). Meanwhile, the GT3 RS produces 772 lbs at 186 mph, 386 lbs at 93 mph, and vary linearly in between, according to Porsche’s GT division boss, and ‘Mr. GT3’, Andreas Preuninger, who was interviewed by Car Magazine (link: A guided tour of the 2015 Porsche 911 GT3 RS – by the boss). That works out to 622 lbs at 150 mph for the GT3 RS - nearly double what the Z06 makes with its most aggressive aero package, which the Grand Sport does without and makes do with stage 2, as mentioned above.

What about traction? Maybe these pesky Chevys have great traction, allowing them to put power down better and, therefore, outperform their competitors despite being relatively down on power. They could be making better use of what they have, saddling and employing every single horse coming out of their more humble power plants whereas competitors don't. Perhaps.. but there is one big problem. The humble Chevy engines also find themselves placed in cars with more humble layouts - front engine RWD cars. Whereas the GT3 RS has a whopping 62% of its weight over the rear wheels, the Corvette has a relatively measly 51% (impressive for a front engine car). Likewise, the GT4 has a far superior 56% compared to the Camaro's 46%. Without better weight distribution, more downforce, or better tires, and possibly even handling, they couldn't have more traction.. Or Could they? Here's where it gets interesting. I think that it is possible they have better traction. But it's not just traction, I think they have more grip overall, allowing every component to perform better. How do they do that, despite (probably) being relatively handicapped or equivalent at best in all aspects mentioned above? Stay tuned to find out in Part 2!

Saturday, 24 September 2016

Car and Driver Lightning Lap 2016 - A Closer Look

Where did the time go? I unfortunately missed last year's feature. I did intend to post about it this year but haven't had the chance and it's already time for this year's feature. I thought I'd get this one done first and then go back to last year's (hopefully). The full article for this year's LL is here: Car and Driver - Lightning Lap 2016. As always, my car picks aren't necessarily very quick or slow. They simply did much better or much worse than I excepted them to. 

The Highs

BMW M2 - 3:01.9: Last year, a BMW M4 did 3:00.7. 1.2 seconds is all that separate the iconic M4 (an M3 coupe, really.. doesn't that sound better?) from this M2. And that one had the dual clutch transmission and carbon ceramic brakes. Opt for the manual, and you could very well be neck and neck. But you save *ahem* about $30,000 in the process, a little more if you're in Canada. That's what you need to get an M4 with the competition package, dual clutch auto, and carbon ceramic brakes. The M2 is also lighter and seems to be hailed as the true spiritual successor to the BMW 2002. The lack of carbon ceramic brakes is not only impressive, but will also make it much cheaper to run at the track. If you want the best BMW M track car, this is the one to get, not the M4. 

Chevy Camaro LT 1LE - 3:04.0: I don't know if I should be surprised. Year after year, the GM team has been destroying expectations of how much track performance you can get for your money. Sure, the Corvette has always been a bargain for what it offered but that's a low, lightweight, two seater, purpose-built car. 

Both 1LE Camaros are knock outs in their own rights and class, but the V6 has more of a David-and-Goliath story to tell. Both cars are huge value and underpowered compared to most of the cars they beat or run with, but the other one has an SS badge and V8 noise and power. This is "just a V6 Camaro." And it is one tenth of a second behind a 2012 Porsche Cayman R. Think about that for a bit. It beats heavy hitters like an Audi RS5, BMW M5, last generation TT RS and, embarrassingly, a current Mustang GT PP. As Car and Driver has been saying for a while now about the 6th gen Camaro; there is no longer shame in buying the V6.

Chevy Camaro SS 1LE - 2:54.8: I'm looking at this a little differently. You want phenomenal value in a track car, you buy a Camaro 1LE. Chevy will generously let you choose two engine options, depending on your thirst for power and the level of car you want to embarrass, although it'll probably really depend on how deep your pockets are. Not a single car that beat either Camaro costs less. It's not possible to go faster for less (off the showroom floor). The SS? Well, that beat the R8 V10 Plus that ran with it this year and was less than a second behind a Cayman GT4.. the GT4. That's despite the Camaro having worse power to weight ratio, weighing around 700 lbs MORE, AND having less sticky Goodyear Eagle F1 Supercar tires vs Michelin Pilot Sport Cup 2's. Swap the tires, and the Camaro is ahead, I have no doubt,  despite the weight and power to weight ratio. Unbelievable. Stay tuned for an upcoming post on how GM works its track magic!

The Lows

Acura NSX -  2:50.2: Three electric motors, mid-engine layout, aluminum and carbon fibre space frame, twin turbo V6, Pirelli Trofeo R tires.. what am I missing? Oh yes, a nearly $200k price tag. The last NSX was well under $100k when it came out. After accounting for inflation, or if you compare to how much cheaper it was than other cars that are still in production (i.e. a 911 turbo, a comparable Ferrari, etc.) or more expensive (i.e. a Corvette or a Viper), this car should cost about $60k less. What do you get for the added money? It's certainly not performance. This car will get beat by a now out of production Ferrari 458 Italia. I remember reading somewhere that this was one of their benchmarks during development. I always assumed that they were referring to driving experience, not performance.. The 911 GT3 (non RS) is two tenths of a second slower. That's zero point two. And it is about $60k less. Since when does a special track edition Porsche qualify as good value? It now does, thanks to Acura.

I get this car, despite how harsh I am. It is a step in the direction of less reliance on gas. The way to look at it is that it is showing us the future can still be fast and fun, despite (some) electrification and hybridization. In day to day driving, it should be more efficient than a GT3 but you give up no performance at the track. But, because of the price, the target buyer isn't buying to save on fuel costs so you buy it because you want to make a statement or you truly care and think it will make a difference. If you are in that latter group, thank you for being the early tech adopter, even though it doesn't make sense on paper, to allow automakers to develop them. Otherwise, there are far more exciting cars for the money that give up nothing in performance, some of which also beat the Acura for far less.

BMW M4 GTS - 2:52.9: Unlike the Acura, this has no excuses. Why doesn't this match the GT350 or Z/28? Why is it over 1 second and 2 seconds slower than those cars? It has half a cage, power turned up to nearly 500 hp, big sticky Michelin Cup 2 tires, functional aero upgrades, and costs more than twice as much as a base M4. All of that adds up to the impression that BMW left no stone unturned. I'm left with only one conclusion; BMW cannot make it quicker. They either need wider tires and/or track but couldn't fit them in the fenders, more power but the transmission, axles, or diff couldn't take it, or stiffer suspension but it was determined to be too stiff for the street, or something else. I really don't like to judge a car by performance on only one track and I expected it to do better at Laguna Seca with Motor Trend, but *SPOILER ALERT* it was only slightly quicker on LS than a Z/28 (less than two tenths is the difference) but slower than a GT350R. Is this the best BMW can do?

Lexus GS F - 3:05.9: This shouldn't really be listed because I (and you should've) more or less expected it to put a time right around what it did, basically tying the RC F from last year that has basically the same drivetrain, including torque vectoring diff, and weighs basically the same. I couldn't help but shake my head, though. Forget the heavy hitters like the CTS-V and E63 AMG S, with times of 2:56.8 and 3:00.1. Why couldn't this beat a humble 2015 Mustang GT that also has a naturally aspirated 5.0 litre V8 that so happens to be more than 30 hp down on power? 

I think Lexus is hoping people compare this car to the competition from Cadillac, Mercedes, and BMW much like comparing a Cayman to a Corvette. The Cayman is supposed to be more focused on driving while the Corvette is more focused on performance. Trouble is, while the Cayman can make a huge statement for itself due to lighter weight, mid engine layout, and more direct feel, this car offers nothing for a purist beyond a naturally aspirated engine. But even that, they took and dulled by a comfort-oriented transmission tuning. No manual, DCT, or at least a more crisp and quicker shift map for the transmission.

I think this car doesn't know what to be. Lexus probably couldn't afford to delay it until they develop a boosted unit so they gave it the older N/A one (albeit, with updates). That means they couldn't compete on raw numbers so had to make sure it's more comfort oriented in suspension and transmission tuning. That isn't a cool selling point in this segment, though, so they tried to sell it off as more of a "purist" choice because of the N/A engine. It's a half-hearted attempt that only exists because they needed a GS F, in my opinion. I'm typically a sucker for a good naturally aspirated V8. Here, though, I can't help but ignore it, because the looks say it's trying (far) too hard while the rest of the car says it's not trying hard enough and the price.. that is just screaming: there are far better options!

Tesla Model S P85D - 3:17.4: A humble FWD, 4 cylinder turbo Focus ST is but two tenths of a second behind this. The Focus is more or less 3 seconds slower to 60 mph and to cover a 1/4 mile, and it's also laughably traction limited, being FWD with an open differential (and only brake-based limited slip programming) vs this mighty multi-electric-motor AWD Tesla. I admit, it's very cool to keep giving this car more power and better launch programming to see how quick it can go from 0-60 mph but the fun AND shock of it is getting old. I hope Tesla starts putting some money and effort into developing a proper battery pack with cooling that can allow the battery to function at peak despite track abuse. This slow time was even despite having part of the lap (first 40 seconds) with full power before battery protection kicked in. Imagine a second, full lap, entirely with reduced power. Tesla gave us the first long range car, charging infrastructure, and good, desirable performance, but all is moot so far for the large (and growing) market of track-day enthusiasts around the world.

Where is my car??

You might be wondering where some cars are or why they didn't make the list. A couple were close calls for me so I thought I'd mention them.

Focus RS - 3:03.9: The RS put down a blistering time and most people probably were expecting to read it in the high list or were at least surprised by the time. I, too, was very surprised at first, then I saw it was done on the optional Michelin Pilot Sport Cup 2 tires. It's hard to say what those are worth but 3-5 seconds seem reasonable to me on a track of this length. Half way in the middle, 4 seconds, would give this car a time of 3:07.9 about 2.5 seconds quicker than an STI. That's very good and, as a Ford fan, I couldn't be happier that it's the quickest car in the segment, and by a large margin, but we already knew it handles better, has more power, and better power distribution bias, so that's more or less where you'd expect it.

Shelby GT350R - 2:51.8: I was disappointed when I first read this, because it couldn't beat the last generation Z/28. I was planning to put it under The Lows. Then I started to read more. The Shelby and Corvette Grand Sport have the same model Michelin tires. However, they found those on the Grand Sport to be more peaky, with great grip for a few laps, and then grips falls off slightly as they get hotter. There is nothing wrong with that. Most tires are like that. You always expect to lose some grip when the tires get hot. In fact, the ones on the Vette were actually good because the tires were very consistent after giving up some edge. The interesting thing, though, is that the Shelby-specific tires were designed to have more longevity than ultimate grip, and the tires never seemed to lose any grip as the laps piled on. This is not only very useful, but also refreshing - to see an automaker committed to something you will probably see very little promotion on (besides Ford advertising they're Shelby-specific spec) but a serious driver will appreciate. And that something could hurt lap times, the one thing most people will remember and reiterate, for the sake of having a more consistent and confident inspiring car. Moreover, as I said under the M4 GTS, when cars are this close in performance, you can't judge based on lap times on only one track and, as you may have read, Motor Trend's Best Driver's Car results are published and *SPOILER ALERT* they're different and the 350R does beat the Z/28 by about a second and a half.

Corvette Grand Sport - 2:47.1: This is more or less the same story as the Focus RS. It seems like a surprising time at first, but then you think about it, and it makes perfect sense - much bigger and stickier tires, upgraded suspension, and more downforce. It sits between the Stingray Z51 and the Z06 in terms of lap times, although it's much closer to the Z06 - 6.7 seconds faster than the Z51 and only 2.5 seconds slower than the Z06 - while being much closer in price to the former - about $11,000 more expensive than the Z51 and $18,000 less than the Z06. But it is justified because, with the Grand Sport, you only get the track performance but not the power. With that said, with apologies to the overlords of automotive power, you don't want the extra power here.. If the Z06 were still naturally aspirated, sure, but I will always prefer a naturally aspirated engine on track than otherwise. And you'll give up very little comfort, thanks to the excellent magnetic shocks and dual mode exhaust, but gain so much in performance. This is basically tying a Porsche 911 GT3. The RS one - costing two and a half times as much, producing 35 more hp, and weighing about 350 lbs less. Both have sticky track-oriented tires and real aero-improving parts. The Corvette does more with (a lot) less. And it's a V8 with a manual..