[gcmbob]

I have been battling with what size tires to use and set my car up for. Ive been thinking that 225/40/17 will give me a nice balance based on the weight of my car and my power range and based that my car will be setup for a 50/50 balance. Of course wider is better but do i really need say 235s all around, given i might be running r888 and the car will only be making about 250 fly hp.

Andrew what size tires do you guys run on the WSC car and if you had a choice what would you run.

As speeds increase does a wider rear tire help...?

Im a little confused about all this.

Remember im 3sge too.

 

[ISZach]

235/40/17 is the ideal tire size for a race car like yours.

 

[Inspar8r]

I'm planning on 235/40/17s for my autocross setup. Mike (DS8) runs 245/40s race rubber. I plan on running Falken Azenis RT-615s (but I'm competing in STX, so r-comps are not allowed).

In my class, we're only allowed to go up +20mm in width, IIRC.

 

[ISZach]

I plan on running Falken Azenis RT-615s (but I'm competing in STX, so r-comps are not allowed).

The RT-615 is still a street tire, not R compound, it's only a 200TW.

 

[gcmbob]

yeah ill prob go r888 if anything. i dunno why 235s intimidae me. Prob cause my last performance car had 195's. LOL.

 

[AndrewW]

We use 235 40 17 in World Challenge, it is the spec size. R888 for this year now.
If I had the option I would run as much tire as I could possibly fit in the OEM fenders which I would suspect is a 255 to a 275 up front. Unless you are running a circuit where you are flat out through most every corner already, lap times should improve with a wider tire. By keeping within the stock body you are not adding a substantial increase in drag, which is very important for your target HP.

We are currently looking at building an all out time attack IS300, with target tire size 335 all around. This would be overkill for your power output, the extra weight of these wheels/tires + the additional drag of the widebody wouldn't help performance, But I would suspect if you ran something like a 255 all around that would be close to optimal.

I base my tire sizing based on weight distribution. More rear weight requires more rear tire. If you are 50/50 as planned, you should be running non staggered tires.

Andrew

 

[gcmbob]

Thanks Andrew. 255's wow. Can that fit under the front fenders? and i would need what? 9" weels?

 

[TeCKis300]

Bob...I'd imagine your car is significantly lighter in the front end so you probably could get away with less front tire than the IS300 demands.

235/40/17, 245/40/17 are all really easy tires to fit under the stock IS300 flanks. You'll need to massage the inner liner for the 245/40/17.

A 255 tire is doable as well with a minor roll of the fender... But I dislike the overall hieght of a 255/40.

A 245/40/17 would really be the sweet spot on an 17x8+45 or 17x8.5 +45 wheel all around without resorting to significant fender mods.

O...and max really is a 255 at the front fenders. Any more...and you'll need to either modify the inner upright or pull the fender or both.

 

[AndrewW]

a 17*9 would be ideal for the 255, I agree it would be nice if they would make this in a 35 sidewall.

Andrew

 

[gcmbob]

I think ill probably try a set of 225's to start, as the car will only compete initially in lower speed solo type events. If i get to race it overseas then ill prob switch to 235's. At that point ill prob be under restrictions anyway.

Great input, thanks

 

[gcmbob]

what offsets would i need for a 9" wheel?

Edit: forget that, Where the hell can i find a decent wheel in 8.5" with the correct offset?

 

[IS_Dude]

what offsets would i need for a 9" wheel?

I would recomend a 47'ish offset in the front. Give or a take a couple mm. Stay close to that. I had a 42 and it rubbed a tad with 245's up front using Kumho Victoracers. With 47 you should be perfect.

 

[gcmbob]

rubbed what? I have no fender linings. If anyone has suggestions on 8.5" wheels let me know.

 

[IS_Dude]

rubbed what? I have no fender linings. If anyone has suggestions on 8.5" wheels let me know.

rubbed the edge of the fender before I pulled it a little, then it just rubbed the fender lining. If you have no fender lining and you ran 47 offset you'll be fine. you'll be fine with the 47 offset even if you have a fend lining most likely.

just to clarify, I had a 42 offset, that's why I am very specific that 47 would solve the issue. I almost turned the wheel down to get it to the 47 to make it perfect.

 

[gcmbob]

only thing i can find is a 42 like you had.

 

[IS_Dude]

well if you want you can find someone who can put the wheel in a lathe and take 5mm off of it if you want to run with a 245. 235 or 225 you won't have ANY issue. I was running 245/45 17 on an 8". It was a beefy tire in the front.

 

[gcmbob]

ooo scary. I guess it is that simple though.

 

[TeCKis300]

I was running 245/45 17 on an 8". It was a beefy tire in the front.

47 definitely won't work with an 9" wheel and is pushing it way to close for an 8.5" wheel. The issue is at the inner upright. You're problem was really the aspect ratio and not so much the width. 25.7" is way too tall overall for the fenders.

Several of us have regularly run 245/40/17s with very little issue on 8" +45 or +48 wheels.

As a firm example, I have run 245/40/17s +48. Yogi_TRD has run the same with +45. Only mod was the liners, which you don't have.

Also, this is 17x8+48 & 245/40/17:

Not even enough room to fit a finger or rim lip balancing weight.

A 17x8.5 cannot have higher than +43. This is a 18x8.5, which can be +45 since the upright slightly curves away:

I run 255/40/18s on my 18x8.5+45 street wheels.

A 17x9 needs a +38 or lower. You will have to massage the fender to work with this.

 

[gcmbob]

So it really comes down to get a 17x8 and stuff what i can in it. Or go for mustang type offsets in a 9 all around.

I think i will stick with a 8" as it gives me leeway in both directions. a 9" i have to run 245's or bigger. And they dont make 245 in r888 and the 255 is a fatty.

 

[IS_Dude]

47 definitely won't work with an 9" wheel and is pushing it way to close for an 8.5" wheel. The issue is at the inner upright. You're problem was really the aspect ratio and not so much the width. 25.7" is way too tall overall for the fenders.

Thanks for the correction. I don't want to pass incorrect info. I'm not sure about the 38 on the 9" though. It will be far out.

The reason I went with such a tall tire was for some specific drivability and traction concerns. I thought it was the correct size and still like that setup on the camber challenged IS and was willing to take the negatives.

gcmbob, take teck's advice. I really wouldn't try to push the size much over 8" in the front from my little bit of experience, but I know some who have.