After our first stint at VIMC we went and made some tweaks to our 3LZ HTC Z06 and went to our favourite local(ish) track, The Ridge Motorsports Park, to try out the car again. The car is still in the stock form with stock tune/power, brakes, and the very street-oriented factory PS4S run flat tires. We found the front end a little muted at VIMC and the turn-in response to be a bit dull, so we went ahead and increased front camber and caster before heading down to The Ridge. Additionally, the car got the Z51 rear sway bar upgrade, a modest 2.5mm increase in thickness, that we did feel helped with the weight management.
To be brutally honest we did not have a target time for this car as we didn't know what to expect with the PS4S tires now on their second track day. Many of the videos we saw were on the upgrade Z07 package which includes the much faster Cup2R tires or track oriented 200 treadwear summer tires, but we wanted to see what the standard issue street tire could lay down and gauge future upgrades on as a baseline.
Drivers' Notes
From the driver's seat, the extra front camber with no added rear camber and the stiffer rear sway may have contributed to the tail-happy nature of the car. Both on corner entry and corner exit, extra caution had to be applied with throttle and steering inputs. The overall balance of the car is still very much there and very much neutral and the car willingly rotates under both throttle and trail-braking. High speed stability was excellent even with no real aero (no canards, no wing, only factory lip spoiler), and the cornering speed through T1 and T10 were excellent. It was in the lower speed corners like the T8A/8B and the T14-16 complex where the car felt unpredictable and took away from the driver confidence. We suspect slightly more rear toe-in and rear camber should help. For this event, we ran -2.5 up front and -2.2 in the rear, so there is a 0.3 difference between front and rear camber. We aim to close that down to -2.5 and -2.4 and increasing the rear toe from 0.1 degrees total to about 0.15
Alignment Review
Upon review of the GM alignment specs (see chart below), we noticed that the trim level and engine options greatly alter the recommended specs. This is not surprising seeing as there are different tire options and a huge range of power outputs on the C8 chassis (from about 500hp to over 1200hp). For all models, the recommended front and rear toe regardless of street or track is only 0.1 degrees total for front AND back. Rear caster should always be set to zero, and a special caster tool is required to check rear caster. Additional labour times will be added for alignments that require rear caster setting.
The Stingray track setup calls for -3.0 front and -2.5 camber, this car has a much narrower front tire and track width so we can see how the 0.5 delta in front camber can aid with rotation. It also makes the least amount of power so straight line traction is probably the least concerning out of the various C8 levels.
With the Z06 the track alignment calls for square camber, meaning the front and rear should stay the same. However we noticed that the spec for FE6 and FE7 is identical and this is where we feel some adjustments need to be made based on the model differences. The FE7 (more commonly referred to as Z07 package) includes stiffer springs and sway bars, significantly more downforce by way of front canards and a taller rear spoiler, carbon ceramic brakes, and Michelin Cup2R tires. The changes are substantial so to imply that both vehicles should take the same approach for alignment is peculiar.
Nevertheless, we will continue testing and fine-tuning our recommended alignments to see what actually works the best for each driver. From our limited testing so far, we find the FE6 (standard Z06) track alignment could benefit in for both turn-in response and rear end stability when paired with the standard PS4S tires. Ultimately, alignment should be viewed on a subjective basis and is an ongoing process based on driver feedback and setup. There is no end all be all alignment and every person's driving style is going to have different needs.
