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Chevrolet 1LE & Grand Sport - How do they do it? Part 3




In Parts 1 and 2 (Links: +Chevrolet 1LE & Grand Sport - How do they do it? Part 1 & Part 2), I concluded that grip is where Chevys excel and decided to try and figure out how they do that by looking at test data from Car and Driver's Lightning Lap features. The first thing that stood out to me when the 5th generation Camaro 1LE came out was the wider tires compared to the Mustang Track Pack of the time and even the Boss 302. The tires on the ZL1 and Z/28 stood out as much.. only on those, they stood out compared to just about anything that isn't a supercar. So I decided to start looking there; tire sizes.

To evaluate tire sizes, I calculated a weight-to-tire-section ratio for each car. Similar to the idea of power to weight ratio, where the number tells you how much weight each hp is burdened with, this tells you how much weight each mm of tire section is burdened with, so to speak. For example, a BMW M235i weighs 3,490 lb, as tested during the LL feature. It has 225/40/18 front tires and 245/35/18 rear tires. The total available tire width footprint, pressure, tread, and tire deformation notwithstanding, is 940 mm (225 x 2 + 245 x 2), which gives it a weight-to-tire ratio of 3.71 lb/mm. Here is where the trust in measured data that I hopefully established in Part 2 comes into play. Without a monumental amount of work going into looking up tire pressure specs, tire wall and tread stiffness spec (IF manufacturers share in the first place), and calculating actual contact patch areas for each car, we can look at measured data (i.e. lap times) and see if we find a correlation strictly between tire size and lap times. Here's a plot of that weight to tire section ratio for each car vs that car's lap time.




You may have read or heard about how wider tires don't increase contact patch size and are only useful for managing thermal stresses and changing the shape of the contact patch. Whether it's due to the contact patch size increasing, better thermal management and patch shape, neither, or both is irrelevant here so I won't get into the theory. What's relevant is the real world result: cars tend to go faster on wider tires. It's unarguable that quicker cars have more tire width for every pound of weight. I couldn't find an advantage in specs in terms of power, weight, downforce, etc. but could tire size be a factor? Below is a table listing different weight to tire width ratios for Camaros and Vettes and a few other cars. If you arrange cars tested over the last three Lightning Lap features in terms of weight/tire mm, the Corvette GS is 4th best, Z06 is 8th best, and 5th gen Z/28 and 6th gen SS 1LE are 14th and 15th, and that's out of 50 cars (excluding special features like race and police cars).


Car lb/mm
Viper ACR 2.62
SRT Viper TA 2.64
911 GT3 RS 2.67
Corvette GS 2.78
Alfa Romeo 4C 2.81
Cayman GT4 2.83
Corvette Z06 2.86
Shelby GT350R 3.00
911 GT3 3.02
Ferrari 488GTB 3.12
McLaren 570S 3.13
Audi TTS 3.16
(5th gen) Camaro Z/28 3.17
Camaro SS 1LE 3.17


Clearly, Chevys measure up really well here. This is something you might have noticed in the past by looking at specs, and Chevy even bragged when it released the Z/28 and said it had the widest front tires (305) fit to a production car. You might have also found a lot of angry anti-Camaro comments on reviews that go along the lines of this: "throw wider tires on [insert car] to match the Camaro and see how it stacks up!" There is reason to the madness. Now, slapping a set of huge tires on a car not set up to handle the grip won't win races without a proper setup and supporting hardware, but the point is that you do need big tires. Chevy's clearly got that base covered. So, is that all, you just need wider tires?

Although they do have good tire-to-weight ratios, you can see from the table above and the one posted in Part 2 that they beat cars (in lateral g forces) with better numbers and, as mentioned in Part 2, they rank above nearly 200 cars in lateral g forces measured in the first corner of the track, which is especially impressive for the current Camaro SS 1LE, since it doesn't use the same type of aggressive tires like the Z/28 and top dog Vettes. If it's just down to this ratio, that shouldn't be the case, so it's likely not the only factor/advantage. What else could it be? Bear with me on this one.. I think it's wheel size. Now, everyone avoids big wheels like the plague. But what if the bigger wheels actually help? Let's first look at why big wheels are bad.

First is weight. Weight is the enemy of speed. Bigger wheels tend to be heavier, so that's more weight you have to accelerate, brake, and turn. Weight is also critical because wheels and tires are unsprung – meaning the car’s springs and entire suspension is downstream of it (relative to the road) and can’t directly respond to forces generated by the road on the wheels. Wheels actually have a suspension system, but it consists of just the tires and air filling them, and those components form the spring and damping properties. Since they aren't nearly as effective as a car's suspension system, especially on low profile tires, they transmit a lot of those forces from the road to the car instead of absorbing and dissipating the energy, and the heavier the wheels, the bigger those forces are. The suspension’s job of keeping tires in contact with the road, then, becomes harder with heavier wheels, resulting in relatively compromised grip and ride, all else being equal.

Then there's moment of inertia and rotational energy. I can't adequately cover these properties here but, putting it simply, moment of inertia is comparable to mass but for rotational motion as opposed to linear. Just as it gets harder to move something the heavier it is, it gets harder to rotate something the heavier it is, but also how far it is from the axis around which you are trying to rotate. If all else is equal, a bigger, heavier wheel results in a higher moment of inertia, making it harder to change its state/speed (i.e. accelerate and brake it). But worse yet, a wider diameter wheel pushes the weight of the wheel's rim/barrel and the tires further out, making that moment of inertia even higher. Moment of inertia, typically referred to as I, is defined as:

I = mass * r²,

where r is the "effective" radius - A distance from the axis of rotation that the entire mass can theoretically be concentrated at with the same result, similar to the idea of a centre of gravity. The heavier something is or the further it is from the axis, the higher the moment of inertia - I - and harder it is to turn. Then there is rotational (kinetic) energy, defined as:

E = 0.5 * I * ω²,

where ω is the rotational speed. That means that the higher the moment of inertia, rotational speed, or both, the more energy there is that you have to deal with. Pretty straight forward.




But what if you could minimize those disadvantages? Chevy has been using forged wheels on their high performance models for a while now. I can't find specs on the 6th gen SS 1LE wheels yet, which may be even lighter, but their 20" x 11" wheel on the 5th gen weighs approximately 28 lb. That's definitely not light, but if you do some research, you'll find that most good aftermarket cast aluminum 18" x 10" wheels weigh low-to-mid 20's lb, unless you get into the more expensive sub 20 lb options. And a cast aluminum would probably have a thicker rim/barrel since it's weaker than forged, so more of the weight is put further out away from the centre, which is worse than just adding weight. In fact, that 20" x 11" wheel is lighter than the 19 x 10" wheel Ford used on the back of the 2012-2013 Boss 302 Laguna Seca, which weighs approx 33 lb, although these were cast. 991 GT3 20" centre-lock wheels weigh 24 lb and 27 lb front and rear (source: Rennlist Forums: 991 GT3 Stock 20 Wheel Weights) and they have to deal with a good 300-400 lb lower curb weight. So, while no featherweight, the weight of those 20 inchers aren't nearly as bad as off-the-shelf 20" wheels that people upsize to for looks and are clearly well designed. 

Rotational energy is a double edged sword. On one hand, a bigger wheel, generally being heavier, negatively affects the weight element of the moment of inertia, making it more resistant to accelerating and braking (i.e. needing more power to do either). On the other hand, a wider diameter wheel and tire package has a longer circumference/perimeter, so one revolution covers a longer distance, which means it can spin slower than a smaller wheel and tire package while the car's speed is unchanged and, therefore, the speed element of the rotational energy goes down. To illustrate, if you compare the BMW M4, which has 255/35/19 front tires, and the M235i, which has 225/40/18 front tires, to the Camaro, you'll find that, because the Camaro's wheels and tires are bigger with a longer circumference, they spin less for the same speed. The Camaro's front tires have a circ. of 7.00 ft, the M4's are 6.81 ft, and the M235i's are 6.57 ft. That means that the M4's tires need to spin 2.79% faster and the M235i's 6.5% faster than the Camaro's to match its speed. And because rotational energy is a function of the square of the rotational speed, the M4 front wheels and tires would have 5.7% more rotational energy than the Camaro's and the M235i's would have 13.4% more energy while all three cars are going at the same speed, if moment of inertia (I) is the same in the E equation above for all three cars.

In other words, more braking power and acceleration (engine) power are needed to brake and accelerate the smaller M4 19" and M235i 18" wheels and tires, compared to the 20" Camaro wheels, assuming an equal moment of inertia (I). I expect the Camaro's wheels to have a higher (worse) moment of inertia, but it has to be at least that much worse for the Camaro's wheels and tires, in comparison, to need the same amount of rotational energy to accelerate and decelerate, let alone more energy. A similar story is true for the rear tires. The overall net affect is impossible to calculate without knowing the wheel's effective radius around its centre, but the point is that, once again, it isn't as bad as people think for well designed and constructed wheels.

So let's say you use light weight and well designed wheels to overcome most of the downside, what's up the side, just looks? I don't think so. Looking back to the data for answers, here are lap times vs (rear) wheel diameter.




Could it be? Do quicker cars tend to have bigger wheels? Only one car with a lap time under three minutes (3:00) uses 18" wheels - the Cadillac ATS-V - but everything else is 19" or larger. Ironically, the ATS-V rides on the same chassis that gave birth to the current Camaro.. and it has very slightly more power along with a fast shifting 8-speed auto vs the manual in the Camaro. Yet, it is noticeably slower, to the tune of a very significant five seconds (for the ATS-V sedan, the coupe is "only" 4.4 seconds slower than the SS 1LE). And, aside from the Viper, every car with a lap time under two-minute-fifty (2:50) uses 20" or larger rear wheels. Quicker cars tend to be expensive, special performance models, exotic, or any combination. You could argue that this makes them more likely to have larger wheels just for looks to match the "status". But there are two problems with that thinking. One is called the 991 GT3 RS and the other is called the Viper ACR.

These two cars are two of the most, if not THE most, hardcore production cars that are dedicated to the noble cause of speed and track performance. The 991 GT3 RS uses not 19" or even 20", but 21" rear wheels. What does that tell you? Keep in mind, that's the same car that, in pursuit of saving weight, does away with door handles and gives you something that James May described as "little bits of rag," in his review of the last generation Boxster Spyder on Top Gear. Do you think they would do that just for looks? The list of weight saving efforts on the 991 GT3 RS includes stuff like carbon-fiber panels for the engine cover, the front trunk, and fenders, a magnesium roof, lightweight lithium ion battery, removal of air conditioning, removal of audio system, centre locking wheels, and lightweight suspension components. It is hugely unreasonable to expect them to go through all of that and simply through big wheels on for looks. The GT3 (non RS) uses 20" wheels, not 21", by the way. The 911 R, the less hardcore, less capable, manual-transmission option that is not obsessed with lap times also uses 20" wheels. The story is similar for the Viper, where the less hardcore TA model uses 19" rear and 18" front wheels. The ACR uses 19" wheels front and back. You can draw your own conclusions.




Do you need more proof? Well, in a Car and Driver test of upsized wheels and tires (link: Effects of Upsized Wheels and Tires Tested), they found that 235/35/19 wheels generated 0.01 lat-g's less than the smaller 225/40/18 (0.88 g vs 0.89 g). Test tires were Goodyear Eagle GT so C&D asked Goodyear for their explanation and "they postulated that the added [tire] width may have given the outside tire more grip, which would increase body roll and could therefore decrease the load on the inside tire enough to lose 0.01 g on the skidpad." No mention of bigger wheels, more weight, etc. or even the suspension not being able to handle the added weight, despite the test car being a 2010 VW Golf with stock 15" wheels that, combined with 15" tires in stock size, weigh 14 lb LESS than the 19" ones.. EACH, meaning the suspension is guaranteed to not be designed to handle the added weight. The trouble was too much weight transfer. A little off topic, but the reason for that is the non linearity between the ability of a tire to generate grip and weight. In other words, two tires with 800 lb on them, each, will generate more grip overall than one tire with 1,200 lb and another with 400 lb, because the increase in friction forces at the loaded tire due to an additional 400 lb of vertical load is less than the drop at the unloaded tire due to losing 400 lb of vertical load.

Back to topic, if you dig a little deeper, the theoretical reason why bigger wheels help is their effect on tires. Bigger wheels better control tire flex under load. Limiting tire flex results in a stiffer tire. You'll hear people refer to sticky tires as "soft compound" sometimes, but there's a difference. You want a soft surface to conform to the road texture and shape but you want a stiff tire structure. Limiting tire flex effectively increases stiffness. And tire grip is directly proportional to its cornering stiffness. Increasing tire stiffness is why high performance cars have low profile tires. The stiffer tires also provide a lot of benefits like better response, less deformation and heat buildup, better stability at high lat-g loads, etc.

Chevy doesn't use the biggest wheels. That would be the rear wheels on the GT3 RS (21") and the front and rear wheels on the Audi RS7 (21"). But aside from those, it uses either the biggest in its class or tied for the biggest. The Camaro uses 20" front and rear wheels on both 1LE models, the V6 and the SS. The Corvette Grand Sport and Z06 use 19" front and 20" rear wheels. I suspect the reason why the Corvette doesn't use front 20" wheels is that it doesn't need to, because its front end isn't nearly as loaded as the Camaro, with a better rear weight bias combined with a more rearward engine placement. As a result, the tires have to deal with less load and can be downsized from the Camaro's. What Chevy is doing is more effectively using wheels and tires to maximize available grip that can be extracted from the tires. This thinking of maximizing available grip extends beyond wheels and tires. Going back to the weight transfer issue from one paragraph up, all manufacturers try to minimize weight transfer for better handling but Chevy goes a step further.

Since weight transfer minimizes available grip, you could throw the best wheels and tires available but if you transfer too much weight, you can't use them to their capacity. Plus, a lot of weight transfer means delayed responses, less stability and confidence, etc. An easy solution is to just increase roll stiffness through springs and dampers, but that also increase vertical stiffness and you may not want to do that. Roll bars are better in that regard, but you increasingly couple left and ride sides if you rely on them too much. The best solution is widening track - the distance between the centre lines of the two wheels and tires on one axle. Performance cars use a combination of all the above, but here's how Chevy's push one step further.

If you exclude light cars like the Fiesta ST and Miata, and exclude very front-end-light cars like mid-engine and rear-engine cars (including front-mid engine like the Corvette, Viper, and AMG GT), the Camaro 1LE has the widest front track for its weight of all cars tested over the last three years, with the exception of the spiritual successor to the BMW 2002 - the M2. Meanwhile, the 5th gen Z/28 had the widest track, period, of any car ever tested by C&D for Lightning Lap features over the same period, tying the Ferrari 488GTB for the honour. Does that matter? Once again, if you look at the data and plot front track widths, you'll find a very clear correlation between quicker lap times and wider tracks. The same is true for rear track.




So far, everything is done to maximize overall grip. The final piece of the puzzle is focusing on longitudinal grip and putting power down - the differential. Namely, the electronic limited slip differential. A differential that can make better use of available traction makes a massive difference in a car's ability to put power down and bringing down lap times. And, to quote Sir Jackie Stewart: "The exit of the corner is far more important than the entry of the corner, with regards to smoothness." You obviously have get the entire corner right to get the most out of a car, but corner exit is more important than corner entry as far as lap times. That's especially true for non-momentum cars like these. I have experienced first hand the improvement different types of limited slip diffs can make but, going by the numbers, a good comparison to demonstrate the difference was done by Car and Driver in 2015 (link: What's the Diff?), putting a Lexus RC-F to the test with the standard limited slip diff and the optional Torque Vectoring diff. The difference was 0.03 lat-g around a 300 ft skidpad (0.94 vs 0.91 g) and nearly half a second (0.4 s) on a minute-nineteen-second (1:19.1) course. That's on an otherwise identical car.

Now, Chevy doesn't use a torque vectoring differential, but a good, electronically controlled, variable locking limited slip differential should be able to provide the same traction benefits of a torque vectoring differential, just not the yaw control due to the steering effect from torque vectoring. The V6 1LE does away with an electronically controlled diff all together, like the one the V8 Camaros and Corvette use, but I suspect that there isn't much to be gained beyond a good mechanical LSD, considering the much lower power output of the V6, combined with the much, much lower low end torque compared to the V8's.

After I concluded that the above seem like the advantages, I started testing my conclusions by comparing those components in Chevys vs cars they beat to see if the advantages do hold up. And they seemed to. For the most part.. there two cars stood out; the 991 GT3 RS and the Cayman GT4. The above components or a combination of them (big wheels and tires, wide tracks, and good LSD's) point to a Chevy advantage for the vast majority of cars but not the Porsches. They do beat their closest Chevy competitors (if classed by specs) - namely the Corvette Grand Sport and the Camaro SS 1LE. But Just.




The GT3 RS is darn near 300 lb lighter than the Vette. It has 40 hp more and far better power to weight ratio (6.3 lb/hp vs 7.5 lb/ hp for the Vette). It has rear wheel steering. It has more downforce. It also uses a variable electronic locking differential, big, wide, lightweight centre locking wheels, and even has a slightly better lb/tire section ratio (2.7 vs 2.8 for the Vette) and upsized wheels (20" and 21" front and rear vs 19" and 20" for the Vette). How is it that all of this nets no more than one tenth - that's 0.1 sec - advantage, despite having Porsche's excellent PDK, which should alone save a multiple of 0.1 sec in total shift times compared to the Grand Sport's 7 speed manual? A similar story is true for the SS 1LE vs the Cayman GT4, although with a bigger time gap (0.8 sec), no auto transmission, but much better tire to weight ratio (2.82 lb/mm vs 3.17 lb/mm for the Camaro). Both Porsches should have a big traction advantage because of engine location. It seemed like it should be a bigger gap for both cars, especially the GT3 RS. That kept hanging over what I concluded, convincing me I must be wrong. But after going through the numbers (a few times), I finally found a consistent advantage - gross tire footprint.

The GT3 RS has a slightly better tire to weight ratio than the Vette as mentioned, but, if you sum up its total tire footprint at all four corners, it comes up 60 mm short of the Vette's - nearly one fifth of a foot narrower. The Cayman has an even bigger discrepancy, with a total tire foot print that's 100 mm narrower than the Camaros, darn near four inches or a whopping one third of a foot narrower. Does it matter that much? Going back to that table of lb/tire section ratio, showing cars that have better lb/tire ratio but don't beat the Camaro in lat-g forces measured in the first corner, you'll probably conclude a resounding yes. Every single car that has a better tire to weight ratio but lower grip (judged by lat-g) has less overall tire footprint, with the exception of the GT350R. But, assuming my earlier conclusions are true, that can be explained with the other factors since it doesn't use an electronic LSD like the Camaro SS 1LE and it has smaller wheels.

Obviously, suspension design and tuning is critical. If not done properly, everything falls apart. And it's critical to ensure the car is fun to drive, stable, predictable, etc. The C&D test I mentioned earlier of upsized wheels and tires is critical in remembering that you have to think of the complete package and the entire car. Putting my conclusions together, assuming they are true in the first place, and making modifications to a car on that basis without proper development, testing, and supporting upgrades is like pitting a Mustang GT and a GT500 against each other in a drag race and, when the GT500 wins, you make the conclusion that you need a supercharger, so you go out, buy one, and slap it on top of the engine in the GT and call it a day. Without supporting modifications and tuning.

The point here is that, assuming proper development from all manufacturers, that seems to be how Chevy carves an edge; wide tires, big but light and well designed wheels, wide suspension track, and good differentials. It seems that, when those are combined with a great chassis and a genuine focus on performance and handling, the results on track or a good back road are very impressive.


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