Autocross Tires

[randymiller71]

Hello, I am new to the forum. I just picked up a 2003 SVT Euro Edition and am involved with SCCA Autocross. Does anyone know what the largest size tire that will fit on the stock 17" rims and not rub? The stock size is 215/45-17. I heard that perhaps a 245/40-17 will fit? Does anyone have any info.Thanks.

[WD40]

Moved to "Autocross Racing" forums.

I take it, you're going to be running HS, hence the stock rim question?

The largest tire that will fit, and the largest tire that will give the best times are two completely different things.

Performance wise:
I would not put anything wider than a 225 on the 7" factory wheels.
Anything larger than that and you'll only be pinching it too much to the point of rounding out the tread where it hits the pavement.

In addition, the larger the tire, the heavier the mass.
Rotating mass plays a huge roll in the car's braking and acceleration.
^^^Even moreso with the SVTF and it's extremely tall 1st gear.
I am WAY faster on 215/45/16 than I ever was on 225/45/17.

Fitment:
225/45/17 is about it, and it's a 50/50 chance whether you'll rub or not.
(I'd say 225/40/17, but only one company makes that size)
A 235 is going to hit the strut body, unless you add spacers.
And, once you do that you're going to hit the fender.
And, again, 235 is just too wide for a 7" rim.

FWIW,
Here's my car on stock suspension with 225/45/17:
http://www.focusfanatics.com/forum/s...ad.php?t=84742


Oh...

[GodLovesUgly]

yeah, what class are you running? if it's not hstock you can get some wider wheels and that would help with 225s in ST, if you want wider it takes you out of ST.

i would pick a class if you haven't already, first. then you can get a better idea of what tire to run. ie, race tires, street tires, width etc.

i was doing a lot of research on wheels and tire size for autocross, and i think if you aren't running DSP or STX 215s will be just fine for you.

[randymiller71]

Thanks for the info, I am still learning about SOLO. I thought that in H-Stock, I could not change the rim size. Are you saying that I could to a 16" rim with Hoosiers and still be legal even though my stock rims are 17", thanks

[randymiller71]

Thanks for the info, I am still learning. I appreciate the feedback.

[WD40]

Originally Posted by randymiller71

Are you saying that I could to a 16" rim with Hoosiers and still be legal even though my stock rims are 17", thanks

Nope...not stock class.
You'd have to stick with a 17X7 rim, though you could find a lighter aftermarket one.
Just make sure you stay within 1/4" (6.35mm) of the factory (49mm) offset, which is harder to find than you'd think.
Most aftermarkets are going to be 40-42mm, and that's out of the range of the rules.
There are a few that can be had in 45mm, which is what I'd recommend.

I'm running ST, hence the 16" rims:
http://www.focusfanatics.com/forum/showthread.php?t=124065

[randymiller71]

Thanks again for your reply. Thanks for the info, I think I will put the 225/45-17 on. I was doing some research however and it appears a 225/40-17 is a little shorter and may also fit. Since the car bogs down in 2nd gear when the revs are down, this may help slightly. What is your opinioin?

Thanks for all your advice. I look forward to becoming more competitive.

[WD40]

I agree, that would be a very good size to run, but the selection is extremely limited.

There's 1 R compound for AutoCross:
Hoosier A6: ($980 for a set. )
http://www.tirerack.com/tires/tires....omCompare1=yes

And, 1 street tire:
Nitto NT555
^^^Which IMHO, would be anything but competitive against the dedicated ST tires available now.
http://www.discounttiredirect.com/direct/findTireDetail.do?pc=40141&counter=1&ar=40&rd=17&sw=false&cs=225

[randymiller71]

Yes, they are very expensive. I found a couple of websites that sell used A6's with 75% life remaing. $145 ea, still expensive considering they will last only one season if I am lucky.

I need to look into the SCCA classes. What is the ST class?

[WD40]

Street Touring.
You must run a tire with 140 treadwear or higher, and no wider than 225 section width.
It allows for suspension mods, and a high flow CAT. (among other things)

You can find (and download) the rules here:
http://www.scca.com/contentpage.aspx?content=61