Jet Vet

EDIT: See response from Aaron Pfadt at the bottom of this post...

In the 8+ months I've owned it, I've put 5,250 miles on my 2015 Z51 A8. Spread out over those months were 6 HPDE days of 45 minutes to an hour of pretty much flat out track time each event. That's all on the OEM wheels and tires with the factory alignment. The tires have held up pretty well, showing normal wear, predominately on the outside shoulders of the front pair.

I recently added LG sway bars front and rear and decided to use PFADT's recommended alignment settings for Performance Street / Track Using Street Tires. I just got the car back from the dealer, asking them to use the settings I gave them, which are an average of the numbers in those two categories in the attached picture. The other picture shows the 'before' and 'after' settings.

On the drive home the car always pulled lightly to the right on differing surfaces and speeds. Looking at the comparison picture, does anyone see anything that would raise a red flag? I'm confused about the sign (+ or -) of the 'Toe' figures front and rear. Also I'm looking at the 'Front Steer Ahead' and 'Rear Thrust Angle' differences. In any case I let the service manager and technician know, but told them I want to drive the car for a while, including a track session next week, to see if things settle in and straighten out. Any thoughts?

JV






I think I can help you out on this.

So, we never ran into much of an issue with pulling on the C5/6 Corvettes, but apparently it is more of a concern with the C7. The OE alignment is asymmetrical – likely to account for a bit of pull. Wide sticky tires and road crown are the culprits, and probably something to do with the revised steering geometry on the C7. The C5/6 car probably had the issue as well, but it was less noticeable.

Exhibit A is the OE alignment for the C7. (see chart below)

By putting in come cross camber in the front (roughly -0.3 deg) right, the pull will probably go away. That is how the factory is doing it.

Our ‘performance alignment’ is still applicable, just use asymmetric camber in front if the pull bothers you.

The toe +/- is tricky because alignment machines from different manufacturers use different nomenclatures. I like negative denoting toe in, but some machines (like the one your shop used) call toe- in positive. I can tell because GM would never put toe out on the rear of a Corvette, and the ‘before’ values are positive. That is confirmed with the after values, all reading positive numbers.

So, in summary, I think the alignment shop gave you what you asked for, and to correct the pull you should add some camber to the right front.

To add complexity to the discussion, see GM’s track prep Guide for the C7. I have run this alignment at the track (on a C7) and actually love it. It’s pretty track oriented, so it may be a bit hard on tires for pure street use. You’ll notice that they drop the asymmetrical alignment in this case. Also, when you lower the car, you can’t achieve both the camber and toe numbers they recommend (for the rear only) without some hardware modifications. You can achieve it with stock ride height.

Hope this helps.

Aaron Pfadt
Advanced Control Engineering