vette ruminator

At the beginning of last summer I bought a set of MPSCs to use for HPDEs. I drive to the track and back, then take them off. They have a total of 6 track days on them, with roughly 36 track sessions, 15 min each. I had been running them at 28 psi cold front, 30 rear, and (as I recall from last summer) they were about 36 psi all around when they were hot.

My fronts have worn as in the pictures you see, with the band just inside the outer tread pattern tapering down towards the wear bars. Once I saw this pattern, I backed off on the pressure to the pressure recommended on the michelin product info: 25 cold/32 hot front, 28 cold/36 hot rear (the cold temps are where I start, the hot temps are the ideal temps from Michelin; I was in that neighborhood). I think it has stabilized, but I did not do tread depth measuring along the way.

Is this pattern normal wear for these tires? Is it not normal and it happened because I was running too hot? Is it an alignment issue (I am running stock alignment as the car is a daily driver except the 6 track days).

I'm trying to get the maximum use out of these expensive tires; how do I know when they are spent (besides the wear bars alone?) I have alternated right front to left front, right rear to left rear between events.

Thanks for your input!

Front tire wear pattern with tapered band inside outer tread pattern:



Rear tire wear pattern more even:

davidfarmer

looks pretty normal for an OEM alignment, but unless you have actually checked the alignment, who knows where you fall (the tolerances are pretty large). I would suggest a more aggressive alignment, even if you stay within the OEM range, going to the max end will certainly help.

Van Steel

i agree with Mr. Farmer, a more agressive setting could help. Remember with stock bushings you will get a lot of bushing deflection so with the added grip you will lose camber in the turns, loading the outside of the tires...

PL

vette ruminator

I appreciate the advice. What settings are recommended to improve this situation but also retain decent drivability for the street without wearing out the daily driver tires?

gamman3

see my old subaru:

It was camber, or lack thereof.

clickable images:

davidfarmer

-1.5 front, -1.0 rear camber. Stock toe (0.1º OUT front, 0.3º IN rear)

You may already have that much, but I doubt it. Most C6Z's seem to have around -1.0 front and -0.5 rear from GM.

froggy47

Flip them. You'll get some extra use out of them. I flip all my track/autox tires (street tires & dotR). 7 years so far no problems.

Pumba

Mr. Farmer is heading you in the correct direction.

An earlier comment about the loss of camber with the stock bushings is significant. You should probably spend the money to have the Pfadt Racing poly bushing kit installed in your control arms. This will help stabilize you lower control arms and prevent most of the camber loss.

The negative 1.5 degrees of front camber will wear the inner edge of your street tires.

Good luck.

vette ruminator

Dirty Howie

I run the specs outlined by David Farmer (except I have ZERO front Toe)

My CUPS lasted a long time but finally got too greasy.

I found that I wanted less pressure in the rears than fronts.

AND it is very important to reinflate the tires before leaving the track. This will minimize wear from non stock camber settings.


DH

longdaddy

I think your pressures are OK as you can see the wear go pretty deep towards the middle.

What you could do is dial in really aggressive track camber (-2.0 or more) and over inflate your street tires to deal with inner edge wear. This would result in your street tires wearing similarly to your pictures, but from the inside to the middle, not to mention more gradually - you would probably get 60-70% of life from your street tires compared to what you get with a more neutral alignment. If you track your car a fair amount, you are probably buying 2 or more sets of track tires for every set of street tires, so you want to make sure your track tires last as long as possible.

I get pretty even wear on the track with -2.2 to -2.3 negative camber in the front and can still get over 15k miles out of street front tires (that double up as an occasional rain tire on the track). Most of my street driving is freeway trips to the track, at the posted speed limit and no messing around with on/off ramps or "twisties", just getting from A to B old man style.

longdaddy

Couple more thoughts after re-reading the original post:

I have no idea how hard you drive your car (rears look a little too mint ) - but 6 days is when most R-compounds start heat cycling out anyway, although PS Cups is one of the more resilient r comps out there. so maybe you don't have much to worry about - as long as you do not see cords when the traction start to drop off dramatically, you're OK. You can usually tell this is happening to your fronts (which harden first) when you cannot get on the throttle as much as you used to in lower speed corners - the car just pushes.

Speaking of rears - you DEFINITELY need to double check your toe there and if it's good, add more neg camber. I have seen this exact wear pattern on Cups on our 911TT with factory alignment, and just adding -0.5 camber made the car feel a lot better. Going from -0.5 or so to -1 should not affect street wear too much anyway.

Coldmale

After 2 years on MPCSs with 2 cars, a C5 & a C6Z06, I got the following

Rear - even wear across the body with 1deg 50mins neg and a shade toe in.

Front - heavy and uneven wear with 2deg 30min neg and a shade toe out. The last set cut through to the cords on the inside after 2500 track Km.

You are not driving hard enough in my humble opinion

I used sam pressures as you 28/30, hot 36

John

Poor-sha

Mine wore just like that until the outside finally corded. I was running -1.5 camber all the way around at the time but did move to -2.3 at the last event before they corded. I do have the Pfadt poly bushings in my car.

With the Hoosiers this year I'm running -2.8 in the front and with the camber kit I've gotten pretty adept and changing alignment before/after the event. I just pop 3 washers off each stud and reset the toe.

I just got back from two days at VIR with the new alignment settings and Hoosiers and I absolutely love the way the car is setup.

vette ruminator

Sean

Did you move to more negative camber for more grip, better wear, or both? Did moving up to -2.3 increase the wear or were the tires just about done anyway? Just trying to get the most out of the pricey Michelins... Glad you've got your ride running well!

mashinter

I got the same inner rib wear on a set of BFG KDs I ran in AX. I did not see that on a set of Kumhos with a much wider outer rib on the same car with the same alignment (-1.25 front camber, -.75 rear camber). Just guessing that the groove is allowing the worn edge to deflect and wear. Visualize a heavily loaded cheese grater running across that open groove and pulling that worn edge into the grater. Dunno.

I drove to the events, and got even tread wear with the street KDs with that alignment, but got more rear wear because I did a burn-out for every AX start!

Poor-sha

I increased the camber mainly to improve track tire wear but I also got a lot more grip and better balance in the process.

I think the increase to -2.3 got me longer life but the tires were close to done by the time I did this. It sucked to throw away 4 tires that had lots of tread except the front outer band was corded. I didn't want to only buy two new fronts since I planned on going to Hoosiers anyway.

This is why I only ran one day at -2.3 with the Hoosiers before I moved up to -2.8 per recommendations from Steve (and previously Frank) who have had even wear with those settings.

vette ruminator

Reviving an old post now that the MPSC ZPs are out there (and waiting for their first event of the year). If I go with about -2 front -1.5 rear for the track, what's your estimate of what PS2s should be re pressure for street use?

Noel

longdaddy

there are quite a few variables involved. on C5, I used to run about 34psi cold

vette ruminator

Thanks for the response. Would u pump up the cups for street driving to/ from the track? Start 2 lbs less than ideal hot temps figuring you'll only gain about 2 lbs with street driving?