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I know it's not a very common combination but I figured I'd give it a shot. I assume alignment principals are similar for corvettes.
I'm currently running Cup 2's with ZR1 wheels on a C6Z with the Z07 package. The car has LG poly bushings and a camber kit. I only drive it to/from track and shop when needed (oil change, adjustments, etc).
I'm currently running:
-2.7 front
8.0 caster
total toe OUT front (.10)
-1.9 rear
total toe IN rear (.26)
The car is great on fresh tires and puts down good laptimes at local tracks. However, it tends to understeer as the tires wear down and progressively gets worse.
When I took off the last set of cup2's, they had about 110-120 laps. All 4 tires had corded with the inside a bit more than the outside. When I did temp tests at the track, the inside 1/3 of the tire does show higher temps but 10-15 degress. This variance goes up as the tires wear down which leads me to my next point.
As the tires wear down, the car turns in normal and then instead of settling and finding grip it goes straight to understeer. It never rolls over onto the edge properly like it does when the tires are newer.
The car is by no means undriveable and is very fast. I'm just trying to get some feedback and opinions on what I could try. If I should just leave it and the cars behavior is normal, I'm ok with that also.
Appreciate any feedback and looking forward to an educational discussion.
There are three things to think about. Tire pressure, actual tire temperature and alignment. Your hot pressures should be between 32 and 36 psi, tire temperatures should be between 160 and 220. You don't mention what your actual temperatures were but only the difference between the inside third and somewhere else. I am assuming the somewhere else is the outside edge. Everything is a balancing act and it is all interconnected. With that negative camber you are already putting pressure on the inside of the tire. if your tire pressure is too high that probably would increase the pressure on the inside edge of the tire since the outside would be lifted more due to the increased pressure and the tendency of the tire to bow outward in the center. That would increase the temp difference more. Based on some of Michelin's data on the Cup tire it looks like 10 deg difference from edge to edge is OK but maybe 15 degrees is too much.
The easiest thing to do would be to lower the tire pressure and see what happens. If that doesn't work then maybe you have too much negative camber and need to drop a couple of tenths. Your toe out will also add more to the inside of the tire but it doesn't look like that is excessive for the turn in you want.
I keep my hot pressures between 32-34 and bleed down as needed.
The temps went from ~180outside to ~192 inside as the tires were new. As the tires wore down, the temps on the inside stayed around the same but the outside went down.
My plan is to take the .5 out of the front camber for now and add some Toe In (.05 total). No recommendation I've seen for corvettes has Toe OUT in front. What I don't know is the following:
1. Is .5 a lot/too much and should i make a smaller change like .3?
2. the rear of the car wears and heats up well and generally feels dialed in. However, are they interlinked? if I take .5 out of the front will the rear needs adjusting also or can I leave that alone for now and just get the front dialed in?
As tires heat cycle they get harder, gripping less & needing less camber. I would lay odds you are heating front tires more, leading to more heat cycle and a harder tire. IE less grip.
I am assuming you are running stock ZR1 sizes with a 285 front 335 rear, if so yes the car will under-steer. Not necessarily a bad thing depending on your skill set, I actually run faster with a bit of push?
You may be a few tenths high on camber especially on the rear. When taking temps lots of time you have to slow way down entering pits which will cool the tire quite a bit slewing results. Really depends on track layout. Slower average speed with lots of turns vs high speed with lots of straights, slower = more camber? Drives me nuts run groups won't let me take temps at Daytona.
There is a balance between fastest and best wear. I have found for best wear I have to run a few psi higher hot in the front due to hard braking wear.
A bit of toe in on front does improve feel at turn in at expense of being darty under hard braking and higher wear.
The PFADT chart is close. You don't have street or race tires some where in between. You are doing great taking temps and logging data, you are using an actual pin pyrometer?
I keep my hot pressures between 32-34 and bleed down as needed.
The temps went from ~180outside to ~192 inside as the tires were new. As the tires wore down, the temps on the inside stayed around the same but the outside went down.
My plan is to take the .5 out of the front camber for now and add some Toe In (.05 total). No recommendation I've seen for corvettes has Toe OUT in front. What I don't know is the following:
1. Is .5 a lot/too much and should i make a smaller change like .3?
2. the rear of the car wears and heats up well and generally feels dialed in. However, are they interlinked? if I take .5 out of the front will the rear needs adjusting also or can I leave that alone for now and just get the front dialed in?
The fact the outside tire temp starts to fall as the tire wears may be an indication of a tire pressure issue. Obviously, something is causing the outside edge of the tire to have less weight on it.
Unless you are good at doing Taguchi Trials I would simplify changes by making one at a time. Try dropping the tire pressure by 2 lbs. Then run 3 laps at speed and measure your tire temps right pit entrance or as close as you can stop to pit entrance. Make as fast of an entry as you can so the tire temp is maintained until a helper can take the temps. After you check the temps adjust the pressure and do another 3 hot laps and repeat the measurements and adjustments to see if you can get a good temp spread across the tire.
If that doesn't work then take .3 out of the camber and raise your tire pressure back to what you were running before. The GM spec shows .1 deg of toe in but then gives you +/- .2 deg of tolerance which gives you up to -.1 deg (toe out). The so called Pfadt specs are all pretty much within the GM tolerance range as shown in the picture below.
FE4 is the Z06 suspension and FE5 is the ZR1 suspension.
If you keep the +8 deg of caster that should still give you a nice camber gain on turn in.
Running the same set up. Using the pfadt performance street/track alignment. Next track day is October 17-18 at Nola Motorsports park. Using full track with the esses on the back. First time on cup 2 using drm bilsteins, and joc sways. Long straights so I'm going with less camber, that's the plan anyway. Interested in this thread
Settings I run on Sport Cups.
Z06, poly bushings, camber kit, coil overs.
Front -2.5 camber, caster 6 to 7.5 degrees, toe 1/16 out
Rear -1.5 camber, caster 0 degrees, 1/16 toe in
34-35 psi hot
Hoosier slicks 18 inch
Front -3.0 camber, caster 6 to 7.5 degrees, toe 1/16 out
Rear -1.8 camber, caster 0 degrees, 1/16 toe in
34-36 psi hot
Good tire wear and temps across the tread with these settings.
Slicks need more camber because the grip level is higher.
Toe out in the front helps turn in but can make the car darty under hard braking.
Toe in in the rear discourages any rear steer.
All radials tires need some toe in or out.
The radial belts need some loading to eliminate belt squirm.
Appreciate all the feedback guys. I will update the thread as I make changes and let everyone know. Hopefully it can help others also.
I was a -1.5 on the rear before and it was wearing out and heating up the outside a bit too much. The temps, wear and grip are much better for my driving at -1.9
Taking .05 of camber out of the front did not work well at all. The front had no bite and I was actually overdriving the front until I changed up my driving to more of a point n shoot style (which in turn killed the brakes)
Anyway, I'll be going back to -2.8 with slight toe out and castor around 8. Something about the devil you know....
10-07-2015, 08:51 PM
Alignment for C6 Z06 with Cup 2's and ZR1 wheels
