I need some help making this decision. First, a little background. So, I'm just a part-time track rat, and only spend about 10-12 days or 5-6 DE's a year, and spend the 3 out of 4 Ohio drivng seasons on regular streets. BUT, my tire purchasing pattern seems to be decided by this small amount of time relative to the whole year. I keep wearing out and cording the OUTSIDE of my tires. In a effort to strike a balance, I installed X73 suspension to lower the ride height, and the stock settings for the X73 also called for a little more negative camber. After drivng to the track and then 3 exhilarating days at Mid-Ohio, on the X73 and new MPSC's, I'm not sure yet but I suspect I'll wear out the utside again.

Here are the rear tires, after a 200 street miles to and from the track, and 3 days of M-O.





Front tire wear is simillar.

The camber settings for the X73 are: -45' +/- 15 front, and 1"40' +/- 15 rear.

What do the track experts think? Keep the current settings until it's for sure wrong, or is this enough evidence I need more negative camber? If you think I need more camber, what's an acceptable compromise street/trackfor what I do? -1" 0' front and -2"0' rear?

Thanks!!

 

What are your tire pressures? The wear looks pretty even across the tire and its not flaring at the edges of the tread blocks. I'm guessing to much pressure.

 

BTW, here's what the suspension/tires look like when side loaded, if it helps any:

 

I started 30F/36R tepid after the street drive when I arrived at the track, and kept bleeding off until it stayed at 32F/37R HOT. Next days, I only checked HOT pressures after the runs, and they stayed fairly constant. Rears went up to 40 in the afternoon, and I just left it there. The pressures recommended by Michellin for the 996 are 32-34F and 37-40R HOT. Pumped them up to 36F/44R tepid for the street drive home.

 

32/37 hot is not too far from what i run. what camber do you have? i suspect less than 2 deg?

 

I usually run mine (of course I know two different model cars but..) at 28-30 cold all four. They are usually very consistant at 36 psi hot. My rear d.s. rolled like yours @ -.8 camber, but the other side at -1.8 is perfect. Fronts don't roll @ -1.0 camber but do flare so I need more there. (all this on stock shocks prior to PSS9's install) Moral is I would still say a bit to much pressure out back. Keep in mnd, if you don't come right off the hot lap(with no cool down period) and take those temps, they're not accurate to the true track pressures. Try staying in the mid 30's out back and see if that doesn't help.

You may also want to try and dial a little weight forward if those shocks are coilovers and will allow corner balancing. Maybe there's to much weight on the rear or just that one side.

 

Palting,

I ran -1.5 front and -2.0 rear with the PSS9's. Stuck with a new set of PS2's, as in no other option not track adhesion , and did not see any unusual wear.
A guy from our club uses and unusual solution to wear. He runs 255 17's on 9x17's on all four corners. Works for him. He is pretty quick with that setup on an 02 C2. He rotates front to rear and side to side.

Anyone else try a setup like that?

 

Thanks for the replies, guys.

John, I run -1"45' on the rear and -40' front, the Porsche recommendations for the X73/C4S. What did you run on your GT3?

Chris, I'm a little afraid to go further down on the pressures. If you look at the second pic, the outside shoulder is already rounded off, with wear down to those little numbers on the side, while the inside shoulder is nicely thick and square on the third pic. On the prior C4S stock suspension, I wore out just the shoulder, not the outside tread but just the shoulder, down to the cords on a relatively new set of PS2's. Cheapo that I am, those PS2's are my current street tires, and I would feel just terrible if I did the same thing to these MPSC's.

Thanks for the tip, Alan. Do you still drive your 996 on the street with those settings? I am considering -1"0' F and -2"0' R for a street and track compromise. Equal tires all around on a 911 sounds a bit too radical for me. It will probably drive the AWD and the PSM crazy . 17" wheels won't fit the C4S brakes, anyway.

 

well, then it seems to me you've come up with the only possible solution......more camber. If your at -1.4 now, I would go to -1.75 rear +/-. Make sure the corner weight values are correctly set too.

 

Thanks, Chris. I think I was just looking for affirmation . I'll see about adding an additional .025-.35 negative camber to the existing settings both front and rear, and corner balance.

 

I can't understand your measurements, but I think you're saying -1.7 deg Front, -0.7 Rear. Is that right? If you had a 993, I'd say go more neg in back, but the front is fine for a dual-purpose car. 993 guys typically run 0.3 to 0.5 more neg camber up front, and I'd think a 996 should be similar (unless you really like all that understeer).

I drove 18" MPSCs with probably less camber than you and didn't get outside wear problems in 11 days of DE events.

 

Interesting - to me, Palting, I think your wear is pretty good, although I do see that the outside edges are wearing faster than the inside, they seem to be wearing pretty evenly. Now I'm confused about mine, as I have two track days (and 250 miles on the road) with my PSC's and my wear pattern is more pronounced, particularly on the edges of the tread blocks. My camber is .5 negative front (max for the stock suspension) and 2 negative rear, I believe (whatever the max was). I was keeping them at 33-34 front and 36 rear hot, which is what Michelin recommends for the Boxster







You can see how the edges of the tread blocks are 'chunking', not wearing as little or as evenly as Paltings. Obviously I chose the worst tire to photograph, and they are wet because I just washed them off to put them back in storage.

 

Eric, it's -0.45 degrees front, and -1.40 degrees rear, within 0.15 degree tolerance. I have the exact measurements at home, but those were the target numbers when I had the car aligned 2 months ago.

You guys are making me lose steam on adding more negative camber. Maybe I shouldn't do it, and use these current MPSC's as test tires to see just how far they will go at the current settings.

 

No do it, you need a hint more in the rear (or you aren't corner balanced and there's to much weight back there). You should be (agian spoke from a 93 perspective) more like 1.75 R, 1.25 F. Thats going to be a bit hard on the tires if you do alot of daily driving, but its the compromise values if you want go track performance.......you'll be buying tires one way or another anyway

 

I think what you're seeing is track crap build up, not your tires chunking. Thats all the marbles on the track you're probably picking up on cool down or in the pits if they're paved.