Wheel Width v. Tire Question

[Jake Stumph]

Hey Gang, I have a small dilemma that I have been asking around for various opinions and hear conflicting thoughts on the matter. I run my 135i in STU where it promptly gets it's ass handed to it, mainly because it lacks the stick of the competition. The narrow-body model can't fit enough rubber under it, especially in the front. Right now, I have a 17x8.5 with a 255/40 RS3 up front. The RS3 runs so wide, that visually, I can tell that it's too much tire pinched onto too narrow of a wheel. However, I'm pretty much maxed out on clearance, inside (strut), and out (fender) as is. However, just by looking at it, I'm inclined to believe that I could at least fit a 9" wheel up front, if I ran a slightly narrower tire, say 245/40? In your opinions, do you feel that this would be a worthwhile trade off, pinching a wider tire onto the more narrow wheel, versus giving up a bit of max tire width to get more wheel under the car? The rear wheels would also be going wider accordingly to match up.

Edit: I would also like to state that right now, even with the pretty heavy rate front springs and a large front bar, I am still seeing a lot of sidewall/edge wear with the RS3 (heavy car). Would I be right in thinking that the narrower tire/wider wheel set up would alleviate this issue a bit since the edge of the tire wouldn't be as pinched?

Thanks,
- Jake

[Richard Jung]

Hey Jake,

Others may chime in with more info, but here's my take. A 17x9 with a 245/40 will be more responsive, and have at least as much grip.
If you are rolling the tire over, you probably need more neg camber. Plus angling the struts inward will give you more tire to fender clearance.
Your front bar may be too big, if you are getting excessive understeer and tire roll over.
A pinched Hankook may need more pressure than other tires with stiffer sidewalls, on a heavy car.
For STU, you can roll/hammer your fender lips flat for more tire clearance, so long as the outside contour is not changed or pulled.
If you haven't done all of the above, you may able to fit a 255 on a 17x9.

Rick

[Jake Stumph]

Hey Jake,

Others may chime in with more info, but here's my take. A 17x9 with a 245/40 will be more responsive, and have at least as much grip.
If you are rolling the tire over, you probably need more neg camber. Plus angling the struts inward will give you more tire to fender clearance.
Your front bar may be too big, if you are getting excessive understeer and tire roll over.
A pinched Hankook may need more pressure than other tires with stiffer sidewalls, on a heavy car.
For STU, you can roll/hammer your fender lips flat for more tire clearance, so long as the outside contour is not changed or pulled.
If you haven't done all of the above, you may able to fit a 255 on a 17x9.

Rick

I should have mentioned, car is corner balanced with negative camber up front maxed out at -3.1*. The issue was much worse on the stock bar, the big aftermarket bar helped a lot, with both wear and understeer. I change pressures re-actively based on grip/wear/pavement,etc. usually ends up being around 30# cold. It's been my experience that the RS3 seem to like starting off lower in pressure than other tires. The fender has been "rolled" from tire contact, so I am not sure how much is left to give there. Thanks for your insights!

[Mark DeShon]

To answer your original question, if you're camber limited, then yes, tire fitment will be more important than tire width. 8.5" is on the narrow side for 255s. However, most STX cars run 255s on a 9" wheel with no problem which isn't a huge difference.
I'm sorry, but I have to challenge Rick on the sway bar statement. Under optimal alignment, he's right, the stiffer end will be overloaded first. However, on a camber challenged car, upping the roll stiffness can keep you working within the more optimal part of the camber curve, and the benefit from this will more than offset the load transfer issues.
My recommendation, do everything you can to make a 255 (or wider) fit. For starters, is 3.1 degrees the max you can get out of your stock top plates, or do you have aftermarket top plates? Generally an ST strut car on Kooks will want north of 4 degrees of front camber. I'm not sure what your strut/upright design is like, but you may be able to gain some camber on the bottom end too. Also on that note, 30 psi sounds a little soft. For reference, the Berry BMW 325is, which should be somewhat lighter than a 135i, runs 255s on 9" wheels, currently 4+ degrees of negative camber, and still in the high 30s for front tire pressure. Try upping the pressure to stand the tire up a bit more.
As for fender rolling, if you want to take this seriously, you should get an actual fender roller and roll the inner lips as flat as possible. (Though I can understand not wanting to do this on a brand new 135i. ) Then, I would take the spring out of the strut assembly and bolt it back into the car. With the wheel/tire mounted, use a jack to take it through its full range of travel. This way you can see exactly how much the tire tucks when compressed. Take measurements from the fully tucked position, and you'll know just how much tire you can run. Also, don't forget to turn the wheel to full lock in both directions to look for rub issues there.
I would bet that if you get your offsets right and a good amount of camber you can run a 255 with a wider wheel. Are you coming out to the February event at Cal Speedway? If so, we can talk more there. I'm in the STU 350z and park in the Berry Compound. Good luck!
Mark D.

[Jake Stumph]

Good commentary, I should have further elaborated: negative camber is maxed out at this ride height, thats TC Kline coils w/ Vorshlag camber plates set up as aggresively as they go. The -3.1* number comes as per Darren @ West End, we maxed the front end out. With this front suspension, the only other way I could see gaining camber would be investing on a possible offset bushing on the lower arms, however, not sure if that is STU-legal, nor even an option, as the aftermarket for these cars hasn't quite caught up the E46/E36 cars. I agree, the front bar keeps the camber curve in it's happy place, i.e. making the best of what the struts have to give under load. Not opposed to rolling, she may be my pride and joy, but ultimately, it IS a 5-year-old car that has seen A LOT of hard miles You all may have seen the car from last year, where I was planing on a full season until about half way through the year when I had start working Sundays. That is no longer the case, so I should be out to every event, barring last weeks event because the car was not ready, so I brought out my DD, the silver Honda Civic Si sedan for laughs in HS. I don't know about every one else, but I am horrid with names, but I can usually remember their cars, so here's mine, if you recognize it:

[Steve O'Blenes]

Hankook 255 tires are wider than other manufacturere 255 series tires. They really need a wider rim than 9" to do their best. I have campaigned on them in my RX8 and I wanted 4 degrees camber in front with more pressure than you are running to optimize. I would recommend trying the 245 as it is a better fit for the 9" wheel with a very square setup and more responsive. They are also lighter and smaller diameter for better gearing. You can also get more camber in the front by either using camber bolts or shims depending on how your strut mounts to the steering knuckle. Older style BMW 3 series would shim the lower mounts. Offset camber bolts can be used if you have a moreconventional strut mount design on that 1 series. What suspension are you running?

Steve O'Blenes

[Mark DeShon]

Nice lookin' ride! I too, am terrible with names, but I have seen yours around some. I haven't been around CSCC much in the past year because I've been raising money to get my STU project off the ground. Anyone in STU has an up-hill battle this year. It's gonna be a very tough class, but I would love to see even more diverse competition. There are a lot of really knowledgeable people who are willing to offer their technical assistance in our region. I'll probably come take a look at your wheels in between my own tuning efforts in February.
Mark D.

[Jayson Woodruff]

Man that sounds low. We haven't ran kooks in a while, but we found them to have relitivly soft sidewalls and it took quite a bit more pressure to keep the stock WRX from rolling over. High 30s at least.
The virtue of soft sidewalls is a much nicer highway ride.

Definitely not going to be your cure all, but it's free to air up. Then you might not have as big a problem as you thought.

Jay W

ends up being around 30# cold. It's been my experience that the RS3 seem to like starting off lower in pressure than other tires.

[Jake Stumph]

Hankook 255 tires are wider than other manufacturere 255 series tires. They really need a wider rim than 9" to do their best. I have campaigned on them in my RX8 and I wanted 4 degrees camber in front with more pressure than you are running to optimize. I would recommend trying the 245 as it is a better fit for the 9" wheel with a very square setup and more responsive. They are also lighter and smaller diameter for better gearing. You can also get more camber in the front by either using camber bolts or shims depending on how your strut mounts to the steering knuckle. Older style BMW 3 series would shim the lower mounts. Offset camber bolts can be used if you have a moreconventional strut mount design on that 1 series. What suspension are you running?

Steve O'Blenes

Shims aren't an option, the strut mounting on the E90/E82 doesn't allow it. The knuckle pinches the strut with one bolt. The strut doesn't use the two bolt fastening solution like a lot of other cars. Here's a pic of my front suspension:



TC Kline Singles which are Koni based.

[Jake Stumph]

Nice lookin' ride! I too, am terrible with names, but I have seen yours around some. I haven't been around CSCC much in the past year because I've been raising money to get my STU project off the ground. Anyone in STU has an up-hill battle this year. It's gonna be a very tough class, but I would love to see even more diverse competition. There are a lot of really knowledgeable people who are willing to offer their technical assistance in our region. I'll probably come take a look at your wheels in between my own tuning efforts in February.
Mark D.

1-series wheel fitment could be best described as difficult, and at worst... I'll spare the foul language.

[Matt Ales]

For my stock class E46 M3 I run 255 on an 8" wheel. The response is so damn slow anyways that I don't even notice but they're consistently faster than 245s. I also run in the low 40s for front tire pressure.

[Kurt Rahn]

...but we found them to have relitivly soft sidewalls and it took quite a bit more pressure to keep the stock WRX from rolling over. High 30s at least.

Jay is a master of understatement. When I first drove on Hankooks, I also used low- to mid-30s PSI based on past experience with other tires. Car drove like crap and was really slow. I talked to Lugod, who pointed out the squishy sidewall and suggested I inflate to 42-44 in front and see how they worked. It was night and day. When I run the Hankooks, I inflate to 42-44 front, 36-38 rear (on a front drive Mini).