^^^ That about sums it up ^^^

I totally agree on sidewall stiffness, stiff sidewalls are much more communicative, so keeping the sidewalls short and stiff, but the tire wide is the best combination for a street car. The opposite of the approach many take in putting the biggest TIRE (not wheel) on the car.

Keep us updated on this.


- So what tires are you running and in what sizes? And what is the size of your rear wheel? I found it very difficult to get the heights aligned right to protect the AWD with a 10" front wheel.

 

Heavy, I've got MPSCs in 265/35/18 front, and 295/30/18 rear mounted right now. I'll switch to 275/35/18 front and 315/30/18 rear NT-01s, or Yokohama AD07s, or similar next, but decided to give the MPSCs a try in their closest sizing first. Ultimately, I'd like to be able to try a 285/30/18 front, but I'll work my way up to that. I know NJ-GT runs that size, but has a GT3, and uses no shims in his control arms, etc... I'd like to see the smaller widths fit first. The diameters are all within 2% of each other, which has seemed fine for the diffs so far. The center diff doesn't start to increase lock up very much until the diameters are different by 7%, according to the PCA technical feedback I've found.

 

Itacud,

Sounds a lot like my suspension except I have the RS uprights. I am curious as to your spring rates. Running a 265 front 295 rear should have cured your midcorner push. What swaybars are you running?? Also what are you running for front toe.

Peter

 

Well, those are some of the compromises I'm forced into, by trying to make a daily use car into something very competitive in it's class on the track. I can't run a giant rear sway bar and stay in the class, nor can I run really stiff springs and drive on the street. I'm using 500lb front, 800lb rear main springs, with 150lb front, 250lb rear tenders. I've already upped the rear rates (main and tender) once, and may end up increasing front and rear rates again - but hopefully not soon. Stiffening the rear would add forward traction, but not w/o a loss at the rear or a non street-able alignment. Instead, I adjust the damping rates to fine tune the balance in all but long constant throttle corners.

I haven't yet tested the new 265 front on 10" front combo on track yet. Still have to eliminate the burning smell under hard cornering. To be honest, I can easily align for neutral to oversteer handling with 235/315 tires on stock rims. But, I can put much more grip into the rear through re-alignment, w/o causing excessively weird tire wear, that it just made sense to increase the front rubber patch.

Toe: 1/32" out in front. I used to use 1/16" out, with less negative camber, but found that decreasing toe out, and increasing negative camber caused for much less premature inside shoulder wear. The excess inside shoulder wear used to occur on the inside tire during a turn, since I don't set the front springs/sways stiff enough to lift the inner tire off the ground in a heavily loaded corner. Initial turn-in speed hasn't suffered much. But, the alignment will be all different in a month. =)

 

I know this is probably a dumb question and you have already tried it. Can you soften the front bar. I work under the premise of fix the end with the problem at that end. Steady state push is probably the hardest thing I have had to dial out and I haven't completely eliminated it in big sweepers. What canister pressures are you running on the motons???

Peter

 

Actually, I just use the tire temperatures to determine which end to soften or stiffen. The low speed compression circuit is very good for that. Outside of the mid point in a turn where the suspension is completely static, it acts much like the sway bars do.

Even with the 235/315 tires, I could drive 4 wheels spinning with the tail slightly out, in 3rd - with the right suspension settings. So, I'm not trying to fix a huge chassis imbalance so much as just get a lot more grip! =) (I incur points for every wheel width change... but it seemed a better use of points for me to change the front by 2", than both front and rear by 1".)

 

Itacud, what class are you running in and with who?

 

Time Trials are with the local PCA region. They use a new convoluted classification system based on vehicle base points and modification points. Unfortunately, it doesn't match the national PCA club-racing system at all.

 

I feel for you, about classing rules. My SCCA T3 S2000 has Moton 3 ways $$$$, (I have to run stock springs and sways) so I have some adjustability. NASA does some of the same except You get to menu shop for what mods you feel are important.

Is it just rim width that costs points or does tire width also cost points. I am curious as to why you are running 295 rears instead of 315's. Also what tires are you running.

Peter

 

Hey Peter. I wanted to give MPSCs a try this time around. Michelin doesn't seem to offer the 315/30/18 anymore, but the advertized section width of their 295/30/18 is big.. They list it as 3/10" bigger than other 295s, though 3/10" smaller than most 315's, on an 11" rim. I forgot to actually compare it to a different 295 (since I seem to be collecting wheels/tires now). I'll have to do that. =)

No points for tire size, but if I were to use Hoosiers, there would be (a lot) more points.

 

Sounds like NASA classing. I know a lot of Vette drivers that are really PO'd that Michelin stopped the 315 Sport Cup. I run street tires for One Lap and am going from PS2's 315's to the new Yokohama AD08 in 295/30. It is as wide, tread width, as the 315/30 PS2 and much better grip. They also make a 255/35 front in the AD08. Diameter on both is 25".

Sounds like what you really need is an open track day to dial in the car. Go out make a lap, come in make a change, go out again until you get a good baseline setup.


Peter

 

You're gonna love the AD08 on track, compared to the PS2. Incomparable. Especially under braking! The PS2 is about 10db quieter on the street though!

Since my MPSC's wheels still don't quite fit tight enough yet, and my NT-01's have been roasted, I'm taking my "wet weather" AD07s to the track this weekend. Even though it will be 104 degrees.

I agree, I do need lots of open track time! So, I've got 5 weekends out of 6 scheduled for track this month and next.

 

Heck I'm pissed too, it's stupid of Michelin not to offer the 315's with so many people wanting them and new markets opening to them. I sent corporate a nice email detailing how ignorant that is.

MPSC are my favorite DOT tire but I don't wish to run stock sizes any longer so they are history. Seems like Porsche pulls all the strings at Michelin because the 315 was discontinued as soon as the 997's were really relevant in the market.

 

Ditto

 

In 2008 we tested AD07's vs PS2's back to back @ Sebring for the One Lap and the AD07's were 2 sec's a lap faster. My only knock on the AD07's is they suck in the wet. My Yokohama contact said they fixed the wet issue with the AD08's and Tire Rack testing seems to agree. As for noisier I couldn't tell as the GT3 had bypass pipes.

Peter