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Old 07-20-2010, 10:25 AM   #1
Dirty25RS
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Default 04 STi wheel & tire fitment

I know this question has been asked a million times.
I searched and what i found was inconclusive.
I dont expect the responses here to be conclusive, but to help guide me.

04 STi.
Stock ride height

Whats the widest tire you can fit w/o fender modification? 245 seems to be it, but i'm posting this thread to ask for clarification.
Whats the right wheel to go with a 245? I think 8" wide wheel but not sure.

Whats the widest tire you can put on the stock 7.5" wide wheel and be safe?

This is for street use, autoX (BSP class), & road racing.

Daily driver/weekend warrior.

I want to ask before I start buying stuff thats not going to fit, since so many before me have fitted various wheels & tires on the 04 STi.
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Old 07-20-2010, 04:07 PM   #2
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I'm looking and thinking about a 245/45R17 on the stock 17X7.5 wheel if i stick with stock wheels. OD will be around 25.67in.

its either that or 235/45R17 @ 25.35in OD

a 255/35R18 will be around 25.00in but would require a minimum 8in wheel width.

stock 225/45R17 is around 24.96in

Last edited by Dirty25RS; 07-20-2010 at 04:15 PM.
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Old 07-20-2010, 06:54 PM   #3
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245 wide is a tough side due to height, as you mentioned. Most people avoid it for the STi (though it makes sense on a wrx with 245/40R17 or 245/35R18). I suggest 235/45R17 if you're going to stick with stock wheels. They're not that wide (7.5" for the 04) so that's about all they're good for.

If you get wider wheels (17x8.5" or 17x9.0"), I'd go 255/40R17. You need a lot of offset (+48 or +50 ideally) and a rear fender roll but it's a lot of tire
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Old 07-20-2010, 08:55 PM   #4
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if your only dealing with the stock 17x7.5 bbs's i would go with a 235/45/17
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Old 07-20-2010, 10:48 PM   #5
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Quote:
Originally Posted by jdmboy View Post
if your only dealing with the stock 17x7.5 bbs's i would go with a 235/45/17
I'm kind of asking both.

A.) whats the largest size you can run on the stock wheels

B.) whats the largest size you can run on any wheel w/o fender modifcation
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Old 07-20-2010, 11:50 PM   #6
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Quote:
Originally Posted by Dirty25RS View Post
I'm kind of asking both.

A.) whats the largest size you can run on the stock wheels

B.) whats the largest size you can run on any wheel w/o fender modifcation
can is different than should, you can run a 245 on a 7.5in wide wheel but it would be pointless because the extra width of the tire wouldnt even be touching the ground. and the steering feel would be **** because of the ridiculous amount of sidewall flex you would have.

as far as how wide you can go, you could probably go with a 245 maybe even one of the narrower 255s without fender work depending on offset and camber specs.
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Old 07-21-2010, 01:34 AM   #7
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I agree with jdmboy
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Old 07-21-2010, 07:43 AM   #8
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I've been racing my car for years. I've come to the conclusion that the 225 width tire on the 7.5in wheel is not wide enough. On the subject of a 245 not using its extra width....It will. 245 is the section width of the tire, not the tread arc width. They can vary independently of one another across tire lines and manufacturers.

I'm not afraid of crappy steering feel if it achieves higher max lateral g's. My Evo has 255/35R18s on 18x9.5 wheels with 25mm spacers on the front. It feels like I'm steering a dump truck but man can it corner tight.

The area of the tire that I think is critical in this situation is the bead area. for a given tire section width, when you change rim width, you are changing the angle by which the sidewall departs from the rim flange. This will have an effect on sidewall fatigue.

But on the subject of sidewall flex, I dont think this will be an issue. Look at a F1 or IndyCar tire. They have gobs of sidewall probably around an 80 series tire. They dont flex. If you find a tire with a taller sidewall with reinforcement it will be better than a low aspect ratio tire.

Low aspect ratio tires are crappy for racing. If it was any good F1 would be using it. The reason its so prevalent in racing anyways is because of the big wheels the fans like, that accomodate the big out-board brake rotors that F1 doesn't have but touring-like cars still need on the track.

a 245/45 will have more sidewall length than a 245/40. This is something I need as I am rolling all the way down to within 1cm of the rim flange on a 225. It will be just as stiff of a sidewall as a 225 if properly inflated.

Thanks for all the input.

It seems the consensus is that 235 is the max on the 7.5in wheel. 245 is the tipping point. And 255 is the tippin point for fender modifications.
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Old 07-21-2010, 10:22 AM   #9
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You cannot apply track to the street like that. You never have potholes on the track, it changes things a great deal. Also, no track car spends such a high percentage of it's life going straight under very little acceleration. A nascar tire? Are you kidding me? What's the average life of one of those, 200 miles?

Don't take our word for this stuff. Go to bridgestone's website and look up different tire sizes for yourself. They specifically list which wheel widths are acceptable.
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Old 07-21-2010, 12:39 PM   #10
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I didn't mention nascar.

taller sidewall tires will be better for road inputs like potholes than a smaller sidewall. The width could provide some additional cushion as well.

Sidewall geometry has little effect on wear. Wear can be accounted for with a 95% confidence interval using a math model involving only tread pattern geometry, tread compound stress*strain @ break, unloaded tire tread shape geometry, load, lnflation, & alignment.

I went to the Tire & Rim Association. They dictate what bridgestone and every other US market tire roughly looks like. According to their calculation, a 245/45R17 is acceptable on a 7.5J wheel. a 245/40R17 requires an 8J wheel.


It seems like this question is all the hang up.

Quote:
Whats the widest tire you can put on the stock 7.5" wide wheel and be safe?
According to T&RA its 245/45R17, but I'm asking for some experienced input from peers.
Also according to T&RA 255/50R17 is the minimum aspect ratio for 255mm section width on a 7.5J wheel.
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Old 07-21-2010, 04:50 PM   #11
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IndyCar (road course)
Front - 254/54/15 (10.0/25.8/15)
Rear - 368/45/15 (14.5/28.0/15)

F1
Front - 245/55/13
Rear - 325/45/13

Not quite 80 series.

I've used 245/40 on the stock 7.5" BBS, no problems, though only for street use.

Since you're BSP (and road racing) I can't imagine why you'd want to use the stock wheels--there is no class limit on wheel.

At 225 - 245 and 3,400lb+ (inlcuding driver), you will likely get too much heat into your tires by the second run or out lap (assuming experienced driver).

265/35/18 fits nicely under rolled fenders with ~ -2.5* to -3.2* camber on an 18x9 +35 wheel. Assuming you have spring rate/travel to keep from bottoming out.
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Old 07-21-2010, 07:56 PM   #12
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Quote:
Originally Posted by gregr01 View Post
Since you're BSP (and road racing) I can't imagine why you'd want to use the stock wheels--there is no class limit on wheel.

At 225 - 245 and 3,400lb+ (inlcuding driver), you will likely get too much heat into your tires by the second run or out lap (assuming experienced driver).

265/35/18 fits nicely under rolled fenders with ~ -2.5* to -3.2* camber on an 18x9 +35 wheel. Assuming you have spring rate/travel to keep from bottoming out.
cuz i got bills son, lol.

I'd love some 18x9 wheels & flared fenders for the STi, but then the wheel bearings would go out all the time so I'd end up getting 05 STi hubs for the stronger bearings, then I'd need 5x114 wheels while i'm at it, and my coilovers wont bolt up to those hubs, so I guess I'll have to sell those and buy some new ones.

thats why I'm on the ****ty (great steering feel) 7.5in wheels.
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Old 07-22-2010, 11:30 AM   #13
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Quote:
Originally Posted by Dirty25RS View Post
cuz i got bills son, lol.
thats why I'm on the ****ty (great steering feel) 7.5in wheels.
Fair enough, though your stable would seem to indicate it's more a matter of resource priority.

You're over-analyizing this... put on some Star Spec's in 235/45/17 and be done with it.

And, I'm old enough to be your daddy, son.
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Old 07-22-2010, 03:42 PM   #14
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Quote:
Originally Posted by Dirty25RS View Post
But on the subject of sidewall flex, I dont think this will be an issue. Look at a F1 or IndyCar tire. They have gobs of sidewall probably around an 80 series tire. They dont flex.
have you considered the fact that maybe race cars dont have side wall flex because they run tires that have side walls that are insanely stiff.

and as far as a street tire if you have 2 245 high performance STREET tires, one on a 7.5in wide rim and one on a 8.5in wide rim the one on the 7.5in wide rim is going to have more side wall flex and worse steering feel. but its not because of the tire compound its because of the angle of leverage on the side wall.
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Old 07-22-2010, 04:16 PM   #15
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And what makes an F1 tire sidewall so stiff?

It may have more sidewall flex, but since its a taller sidewall, it'll keep the rim flange off the ground better than the 225 i currently run on.

I dont understand when/where having a short sidewall became considered good for performance, its not. Its good for fitment and appearance.

I'm not debating if a 245 would perform better on a 7.5in wheel or an 8.5in wheel.
I'm debating if it will be safe on a 7.5in wheel. T&RA says yes as long as its 45+ aspect ratio.
Steering feel isn't important to me. feelings have no bearing on how a car actually performs. I speak in measurable terms, like lateral g's. I want lots of them.

My Evo has 255/35R18's on 18X9.5 ET+40mm wheels with 25mm spacers up front, none in back. The eccentricity of the contact patch with respect to the steering axis combined with the size of the contact patch creates wagon wheel steering to some degree, ****ty steering feel, but it can pull amazing lateral g's, which means it can carry its speed through corners.
Thats why it took 1st in the AWD Street class @ nashville speedway redline time attack.

My point with that little blurp is that I dont care about "feelings" and driving thrills. I care about measureable performance. Lap times, lateral g's, fore & aft g's, etc.

and safety.
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Old 07-23-2010, 01:28 PM   #16
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I don't understand why people are so preoccupied with the 245/235/225...as someone already pointed out the actual tread width can very between manufacturer even within the same size of 225 or 235 or 245...I run a 225 that has a tread width of 9.1"...look at tire specs and decide from there the stock sti re070 is a 8.9" treadwidth tire...dont just go for the 245 b/c it sounds wider...look at tire specs and dont waste your money
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Old 04-20-2011, 01:46 AM   #17
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Quote:
Originally Posted by Blackmojo View Post
I don't understand why people are so preoccupied with the 245/235/225...as someone already pointed out the actual tread width can very between manufacturer even within the same size of 225 or 235 or 245...I run a 225 that has a tread width of 9.1"...look at tire specs and decide from there the stock sti re070 is a 8.9" treadwidth tire...dont just go for the 245 b/c it sounds wider...look at tire specs and dont waste your money

I agree tread width is what we are looking for. As an example a Yokohama Advan Neova in 255/35x 18 has a tread width of 10.1 while a Dunlop direzza in the same size has tread width of 9.1 Same size different manufacturer different width.
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