karlooz

will 265/35-18 wide MPSCs fit on an 18x8.5" rim (front)? tire rack recommends 9-10.5" widths for the 265 but i am wondering if i could squeeze one on. currently i am on 235/295-18x8.5/11. wondering if i could go 265/315.

tia

GT3 Chuck

it will fit the wheel...you need advice from someone who knows if it will clear the fender...I have 275's on 8.5" wheels on my racing Cobra no probs...

jrgordonsenior

Couple of problems......the tire shoulder would roll too much causing a loss of traction. The 265's are as Tire Rack says, designed for a larger rim. I ran them up front on 9-1/2 inch BBS's on my TT, but it required 3 degrees of neg. camber and the right offset to clear. If you're trying to solve a understeer(push) problem, try softening up your front bar a notch. The 235/295 is a usually a good combination for that car.

Z06

On my car I use the 265 MPSC with 2.5 to 3 degrees camber... the tops have been rotated.
at complete lock it will rub on the inside when turning left...or maybe right ..but it only does it in one direction.
If you move the control arms from right to left it will fix the inside rubing issues..which are not bad to start with.

By changing the sway bars.. what you are doing is changing the steady state cornering.
not the turn in. shocks adjustments work on turn in.

jrgordonsenior

One would need to drive the car to accurately assess the issue, but softening the Motons would certainly help. I noted that he has a blower on that car and I'm guessing that he's pushing up front pretty much all the time he's on the gas.

karlooz

yup, pushing in the slow corners, even before the blower. i have almost -2 degrees of camber up front and -2 in the rear. gt3 front sways are right in the middle and the rears are at 2 from stiff. motons are ususally at 3 compression/4 rebound front and 5compression/4 rebound rear. 450# springs front and 700# rear.

the current 295s on 11" rims seem a little stretched spwawning the idea of going with 315s on the rear and further feeling the need to match it with 265s up front. i was hoping i could lessen the slow speed push with bigger meat. currently i've been rotating the car by throttle. it works but keep thinking i am scrubbing speed.

Z06

As far as shocks go... compresion controls the speed a wheel receives weight transfer and rebound is how quickly the weight leaves a wheel.

If you want to reduce the understeer keep backing off on the front rebound and or stiffen the rear rebound.

It's all about testing.. so do one thing at a time... try the front and go step by step a soft as they can go and see what it does... One turn at a time.

next for the rear keep going stiffer untill you max it out...

The ideal for your 265's is to use a 9" or larger rim. .. you can get by with the 8.5"rim.

You need to get a pyrometer..get tire temps and see how much of the tire is working...
Add more camber up front.. 3 to 3.5 degrees.
All these steps will reduce understeer.

earlyapex

You need more negative front camber.

karlooz

tell me about it. i either have to slot the mount holes or go for RS control arms to get more -ve camber. i figured slotting the holes would be the cheapest and easiest way but invasive so i thought wide tires would be an option.

karlooz

great, thx for the tips.

NJ-GT

The 235 MPSC is a skinny tire, and it causes understeer in slow turns, no matter the extra camber. I run -3.5 degrees camber at the front and -2.5 at rear.

Adding extra negative camber, will decrease the braking grip, and these cars are front brake biased. However, you need more than -2 degrees negative camber at the front. The sweet spot on my car is -3.2 to -3.5. To get back the braking grip, a wider tire is needed.

I've tested the 235/295, 265/295, 265/315 MPSC combo on the stock 8.5"/11" GT3 wheels, and I liked the 265/295 combo better. By the way, the euro tuner Koro (4.8 and 5.0 GT3) uses the 265/295 combo on 9"/11" wheels.

The GT3Cup uses a 24/27 tire combo on 9"/11" wheels. These tires are the equivalent in section width to 250/285 DOT R-comp tires.

The front tires in all the current Porsche street cars are undersized in my opinion.

karlooz

thx NJ-GT

so the 265/315 wasn't to your liking? was there too much grip in the rear and presented more understeer?

nmex

I hope not I just order a set track wheels just like that all do the fronts are 18x9 and the rears are 18X12 From s-cargo but same tire set up 265/315 hope to used them these weekend @ MSR houston

NJ-GT

The 315 MPSC is too wide. It doesn't go well on 11" wheels, but it fits. The sidewalls feel softer. In my experience, the 315 felt numb on my stock wheels compared to the 295 that felt precise. I think that on a 12" wheel it should work much better.

However, the 265 on my stock 8.5" wheels feels great. I check tire temperatures and pressure at every track event I attend. The temperature readings from the front and rear tires are ok.

Z06

I do not think a 12" rim will fit the GT3.. The largest seems to be 11.5"