alprus

Looking for a good tire combo for street and DE events. I don't have the abiltiy to have two sets of wheels right now (I drive my car to all DE events), so I am looking to upgrade from my current stock 225 & 265 sizes.

I plan on buying some CCW 8.5 and 11 C10s very soon. Just torn on the tire sizes - I plan on staying with PS2's for now, as they have treated me very well. Anyone out there who has run 245/35/18 and 295/30/18 on the street and track? Worried about the balance changing to too much oversteer, but not sure I want to go to 315's in the back.

Any advice would be great.

Thanks,
Adam

Paul 996

you will be fine, your balance won't change towards oversteeer. Without considerable negative camber in the front the extra wide tires won't even do very much more than the 225.

Just remember that on the 11 inch rim you can go much wider than the 295 and use a 305 or a 315. Just pay attention to the profile.. You really have to stay with a 295/30, 305/30 etc. The 35s will rub.

2cts

Pilot_951S

Don't get to crazy with super large tire the benefits are small and the negatives are large. The stock GT3 setup of 235 front 295 rear is probably the best compromise. If the front tires get too wide you will experience an increase in tram-lining. Also don't forget that the bigger the wheels and tires get the worse the car rides, the worse the fuel economy and the more mass and friction you car has to overcome on track results in slower lap times.

As for the PS2 it is one of the best street tires around but it is not a track tire. I suggest you think about some of the streetable track tires like the Toyo 888 the MPSC (which I don't personally like) the Nitto NT01, or the Yokohama A048.

Trj

I use 245, 295 for the track and they work great. The 11" wheel will take a 315 but hp is a consideration. I liked the 315 set up on my GT3 and have not ran more than 295 on my 996 ( non gt3 ). The 245s up front feel fine.

Pilot_951S

Trj,

What are you using for tires. Obviously Kumho and Hoosier don't make a 235 so that moves you into a 245. Just curious what you are running, and pressure etc.

auto-xr

Here are some PS2 sizes for the rear.

PS2 Size Max Load Weight Rim Size Sec Width OD
295/30ZR18 1653 lbs. 26 lbs. 10-11" 11.9" 25"
315/30ZR18 1653 lbs. 29 lbs. 10.5-11.5" 12.6" 25.5"

Any insight on whether or not the extra .5" in diameter (CG and gearing) and the extra 3#s in unsprung weight would hurt more than help?

Here is another good thread on the subject.

https://rennlist.com/forums/showthre...ferrerid=43587

Trj

Hoosier R6 245 40 front, 295 30 rear, running 38-39 hot.

Pilot_951S

Trj,

Forgive my ignorance of your setup, as you can see from my post count I've been out of touch for a while, what are you running for suspension? Dampers, Spring Rate, Sway bar sizes etc. Have you ever tried 42-44 psi hot rear? Also how much does your car weigh with driver and fuel?

auto-xr

IMO the 315 is not as good a choice as the 295 for anything less than a 400hp car.

On a street car most of these things will be negligible but there are a few things that you may notice especially on track where it can be measured..

The extra weight will have a negative impact on ride quality on the street. The added rotational mass will slow the car's acceleration.

The taller rear tire will have a negative impact on acceleration but you may not notice this on the street. You will notice this on track. Also the taller rear tire artificially raises the rear center of gravity, which again you may not notice on the street but would notice on track.

If you are sticking with an 11" rear wheel the 315 may not behave as well as it should (every tire is a little different). You will find reference to this phenomena in the other thread you linked to. The reason is that if a big tire is installed on a relatively narrow wheel it takes the sidewall out of tension. If you look at the stock 295 MPS2 on the 6GT3 you will notice that the tire seems stretched over the wheel. This puts the sidewall in tension and improves tire performance. Jamming a big tire on a narrow wheel does precisely the opposite. Note that the 7GT3RS has a 305 on a 12" rear wheel for this reason.

Trj

Trj,

Forgive my ignorance of your setup, as you can see from my post count I've been out of touch for a while, what are you running for suspension? Dampers, Spring Rate, Sway bar sizes etc. Have you ever tried 42-44 psi hot rear? Also how much does your car weigh with driver and fuel?

auto-xr

Motons, 2 3\4 rear 3 front - , 750/550 spring rate, 3085 lbs at last event.... I have run the same tires on a stock set up 997 gt3 and they ran great. Anything over 41/42 gets slippery imho.