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Shocks: DRM Bilstein with polyurethane upper shock bushings
Alignment:
Front
Camber
= -1.7 deg.
Castor
= 8.0 deg.
Toe
= 0 deg.
Rear
Camber
= -1.0 deg.
Toe
= -1/16"
Ride Height:
This is a bit of an unknown. I bought the car used and very low miles, but I suspect that it was lowered by the previous owner. I don't know how to check this or what the OEM specification is.
I went to a NASA HPDE in October at the new Dominion Raceway track in Virginia. This is a short (2.0 mile) fairly technical track that runs counter clockwise. On Sunday with warmer temps I could feel the front end sliding more (understeer) and I decided to check the condition of the tires. I always monitor the tire pressure before and immediately after a session, and would go out cold with 27 psi and come in hot with 34 to 36 psi depending on traffic and speed. The photos below show some elevated tread smearing on the fronts and some moderate smearing on the rears. I've run this alignment for the past two seasons and the tread wear if pretty uniform. I street drive the car too, so haven"t gone crazy with the alignment.
Front Driver's Side:
Front Passenger's Side:
Rear:
Does this look normal/reasonable wear for MPSS tires and this alignment. The car definitely tends toward understeer and I would like to tune some this out and get to a more neutral balance under hard cornering. The other handling issue I want to get sorted out for the coming season is the rear end shake at speed when shifting or lifting in transition to braking at the end of a high speed straight. I've read a lot of commentary on this quirk of the Z06, but there is no clear consensus on the cause or cure. I'm still running on stock rubber A-arm bushings and I am going to change to delren for 2017. The DRM Bilstein shocks made a good general improvement in ride and handling and I would like to stay with those another season if I can.
What should I be focusing on, tires, alignment, tire pressure, tire size, bushings, bars, damping, ride height, other?
Tire size can help balance either wider front or narrower rear. Alignment depends on track and your skill and comfort level. If you compare the same setup on the same track with two different drivers it can be great for one guy and bad for the other. I say this to illustrate there is not always one setup that works. That being said I would start by putting 1/8" total toe out in the front and it should help turn in. It will wear tires a bit on the street.
The tires look normal. That's not tread smear its rubber pickup from the track
No kidding?? It certainly seems plausible, but I've never had this much "accumulation" of rubber on the tires before. Otherwise, they seem OK.
Originally Posted by 6SPEEDZ
Tire size can help balance either wider front or narrower rear. Alignment depends on track and your skill and comfort level. If you compare the same setup on the same track with two different drivers it can be great for one guy and bad for the other. I say this to illustrate there is not always one setup that works. That being said I would start by putting 1/8" total toe out in the front and it should help turn in. It will wear tires a bit on the street.
I'm thinking of going back to the 325/30-19 on the rear tires and keeping the 285/35ZR-18 fronts to see if the front end will stick better and reduce understeer.
Installing vansteel bushings now, you will amazed on how much movement there is in our rubber bushings.
I looked at the Vansteel bushings at Carlisle, and they are very high quality. You should post some pics with a short DIY. I'm very interested in how they work out for you.
"OPR" or Other Peoples Rubber. When you get faster it will start slinging off and sound like someone is shooting off a .22 under the car LOL....chased my tail a while on that one, the board here helped.
Tires are normal and wear looks good, they get hot when on track and some of it is that tires rubber coming off and picking up other rubber.
Left front looks a little worn on the outside, this must be a clockwise track. I might put a little more camber in.
See the black marks on the car behind the front tires? It's that stuff coming off.
Try a little lower start pressure. I've found is that if the tire gains more than 5 psi over the course of a session drop start pressure until it gets into that 5 psi window.
Last edited by FASTFATBOY; 12-31-2016 at 05:30 PM.
I suggest a little more camber in front and rear (2.5 and 1.5) and check the ride height (measure at the top of front fender). Don't lower more than 1/2" from stock unless you have a spindle lowering kit. Watch tire pressures.
You can also upgrade your A-arm bushings. They deflect in the corners. Harder bushings will lessen the deflection and keep camber in the front wheel so that the tire does not roll over and punish the edge. My street vette has Urethane bushings and my race car has monoball spherical bearings. The race car is awesome but you can't drive monoball on the street.
Tire turds are normal. The rubber feathers off as the tires is pushed across the pavement in the corner. This is why you have lots of black streaks on your nose, hood and windshield (tire debris thrown up from cars in front of you). If you ever go off line into the outside of a sharp corner, you will find the marbles, a slippery set of rubber turds thrown off from all the cars.
"OPR" or Other Peoples Rubber. When you get faster it will start slinging off and sound like someone is shooting off a .22 under the car LOL....chased my tail a while on that one, the board here helped.
Try a little lower start pressure. I've found is that if the tire gains more than 5 psi over the course of a session drop start pressure until it gets into that 5 psi window.
On Sunday, there was definitely a lot of rubber on the track and it was slinging off! I'm going to keep working with the tire pressure to see if I can keep the gain under 5 psi. Does anyone use nitrogen in track tires? My two daily drivers have nitrogen fill from Costco and they don't vary by more then 2 psi from summer to winter. Would nitrogen hold more even pressure in track use?
Originally Posted by TorontoC6
I suggest a little more camber in front and rear (2.5 and 1.5) and check the ride height (measure at the top of front fender). Don't lower more than 1/2" from stock unless you have a spindle lowering kit. Watch tire pressures.
You can also upgrade your A-arm bushings. They deflect in the corners. Harder bushings will lessen the deflection and keep camber in the front wheel so that the tire does not roll over and punish the edge. My street vette has Urethane bushings and my race car has monoball spherical bearings. The race car is awesome but you can't drive monoball on the street.
Tire turds are normal. The rubber feathers off as the tires is pushed across the pavement in the corner. This is why you have lots of black streaks on your nose, hood and windshield (tire debris thrown up from cars in front of you). If you ever go off line into the outside of a sharp corner, you will find the marbles, a slippery set of rubber turds thrown off from all the cars.
Thanks for the great feedback! I'm going to do the delrin bushings this winter and then I will experiment with more negative camber. I'm hoping the bushings will tame the tail wagging at high speed. This seems to happen when shifting gears and lifting throttle before applying the brakes. I think this is caused by the rubber bushings suddenly unloading and changing the camber and toe angle in the rear suspension. Some cars have it and some don't and I think this could be a function of bushing wear.
"Tire turds" were definitely leaving a lot of black streaks on the car. This was my first outing with NASA and those boys are pretty quick. They were having regional TT qualifications and lots of rubber was sacrificed! I never realized it could clump up on your tires so much.
Pretty obvious your rear tires are oversized from the fronts. I think you'll find better balance dropping the rears to 335, or staying with stock, though at stock you may get in closer to oversteer so be aware of it.
Perhaps some of the more experienced can verify, what I do is start out low on pressure at the first run. I'll run 26 on the front outside tire (most highly loaded), 27 on the inside and rear tires. When I come in, I'll drop all to 30 and check pressures for the remainder of the day, and monitor the amount of tire roll to make sure I'm not rolling too far into the sidewall. If I am, I'll add a couple of psi to compensate.
12-30-2016, 07:23 PM
Chassis Setup and Tire Wear - C6 Z06
