The Ram's Eye - A Driver's Blog: Chevrolet 1LE & Grand Sport - How do they do it? Part 3



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Wednesday, 21 December 2016

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




GM, in general, is starting to build a very strong reputation for chassis engineering but Chevrolets, in particular, have very strong performance on track these days, not just good handling feel and fun to drive attitude. In Part 1 (link: Chevrolet 1LE & Grand Sport - How do they do it? Part 1), I looked at different aspects and concluded that Chevys appear to have the advantage in grip. If you are still unsure that grip is where those cars excel, perhaps this number will change your mind: 1.11. That's how much lateral forces, measured in g, the 2017 Camaro SS 1LE generated in Turn 1 of Virginia International Raceway (VIR) during Car and Driver's Lightening Lap 2016 feature. 1.11 g also happens to tie the 2014 Viper TA, the 2014 Ferrari F12 Berlinetta, and even the 2016 Ferrari 488GTB. It gets more interesting too..


Car Max Lat-g
2015 Chevy Corvette Z06 1.20
2017 Chevy Corvette Grand Sport 1.19
2009 Mosler MT900S 1.16
2015 Chevy Camaro Z/28 1.16
2015 Porsche 918 1.16
2015 Nissan GT-R NISMO 1.15
2016 Dodge Viper ACR 1.15
2016 Porsche 911 GT3 RS 1.14
2015 Lambo Huracán LP610-4 1.13
2014 Ferrari F12 1.11
2014 SRT Viper TA 1.11
2017 Chevy Camaro SS 1LE 1.11
2016 Ferrari 488GTB 1.11


If you pay attention to the order, you'll notice that the list isn't arranged in order of age or model year - i.e. starting with the Camaro, being 2017, then the 488GTB, being a 2016, then the Viper and F12, both 2014 cars - or vice versa. Despite all being listed at 1.11 g, the order goes F12, Viper, Camaro, and 488GTB; two 2014's, a 2017, and a 2016. Unless you want to believe it was random, that must mean that if you look at more decimal places, the Camaro beat the 488GTB and was beat by the F12 and Viper. That's a humble pony car beating a purpose built, mid-engine (new) Ferrari in grip.

It also places 12th out of every car ever tested in Lightning Lap features. The tally adds up to 201 cars and this Camaro beats 189 of them, including cars like the 458 Italia, 911 Turbos (pick a generation, it beat them all), 991 GT3 (non RS). Cars that beat the 2017 SS 1LE include stuff like the GT-R Nismo, Viper ACR, 911 GT3 RS, Porsche 918, you get the picture. Going further up the hall of fame, you find that three of the top 5 cars are Chevys, taking 1st (Z06), 2nd (Grand Sport), and 4th (fifth gen Camaro Z/28). The Mosler MT900S managed to just barely beat the Camaro (both are listed at 1.16 g, meaning they must be separated by a few 1/1000th's), but everything else is beat by the top dog Corvettes. I think I rest my case that Chevy knows grip. And it's easy to see why Chevy focused on grip.

If you can't grip the road properly, you can't put down power, you can't brake as aggressively, you can't carry speed through turns, etc. That's why everyone who's been around a track a few times will tell you that tires are one of, if not the most, crucial piece of the going-fast puzzle. If you have good tires, generally resulting in better grip, any individual under-performing aspect of a car doesn't necessarily have the same effect on others. For example, a low-powered car doesn't necessarily mean it's slow - it could have great brakes, great handling, great downforce, or any combination. Not having much power hurts acceleration, but the brakes can still do their job slowing the car down, suspension can do its job keeping tires in contact with the road, aero components can still generate downforce to increase grip at high speed, etc.

Even within one aspect such as handling, for example, you could have a car that understeers on entry - a bad handling characteristic - but it could very well be good at putting power down. You could still be quick if you slow it down, turn it, nail the apex, and hammer the throttle. Tires, on the other hand, can single handedly ruin all aspects of a car setup and prevent ALL of them, simultaneously, from performing properly if not chosen well and grip is compromised. Conversely, they can improve every single aspect of the car, if maximized. The question then becomes this: how do they generate more grip? It isn't compound because, while they do use good tires, they don't use anything more aggressive than what other manufacturers use (aside from manufacturer specific tuning).

To try and figure out where Chevy's stand out in any one area, or if they do at all, I looked at Lightning Lap numbers in more detail. I collected data from the last three Car and Driver's Lightning Lap features about each car, including lap time, front and rear wheel and tire sizes, front and rear track widths, power, torque, and weights. Then, I trended a bunch of different parameters about the cars vs lap times to see if I find any correlations pointing to a Chevy advantage. First, look at this graph of lap times at VIR during C&D Lightning Lap features vs power to weight ratios (expressed here in the inverse, lb/hp ratio) for the cars.




This isn't relevant to figuring out how those Chevys go quicker, but I just want to establish trust between you and data, if you're someone who isn't used to looking at empirical data, and making observations and conclusions, without knowing all factors. Generally speaking, cars with better weight to power ratios are faster. You probably already know that. But if you didn’t and you had no idea how power and weight affect a car, you’d look at that graph and say that as this weight-to-power ratio number goes down, lap times go down. Here's another graph.




This one is of lap times vs weight distribution over the front wheels wheels (i.e. the lower the number, the less weight there is on the front axle and tires as a fraction of curb weight; more rear weight bias). You could also look at the lap times vs weight distributions and say that front end heavy cars tend to be slower and as you move weight to the rear wheels, cars tend to be quicker. You could make this correlation, and the above between power-to-weight ratio and lap times, while all other factors are unknown - some of which are actually crucial to the going fast puzzle - just by looking at the test data. And you'd be right. With that in mind, can we use the data for more? Even without a deep dive into suspension geometry and roll centres, torsional stiffness, spring and damping rates, etc., can data point to a Chevy advantage, in the suspension or otherwise? Stay tuned for the conclusion tomorrow in Part 3 Chevrolet 1LE & Grand Sport - How do they do it? Part 3!


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