msilvia

In searching I've seen a few people here and there mention this setup, but would like some additional confirmation as to fit.

I'd like to run 255 tires in a square setup. The car has GC/koni coilovers and the RP trailing arms and toe links. Ride height is about 25" all around but I'm thinking of going to 25.5.

The car is a weekend car that will likely see decent track and autox use.

Would this rub in the front under hard use? Will a fender roll be necessary? More?

Any guesses as to whether this would clear stoptechs? Possibility in the future that I'd want those as well.

HalifaxFD

iTrader: (18)

I have 18x9.5+45 all around with now issues, 255/35/18's. I can't speak for the stop techs though.

scarified

18x9.5 +45 is a confirmed fitment for the StopTech's. I'm not sure if the 9.5 +38 will fit it. 17x9 +45 does NOT fit, if that helps.

$lacker

iTrader: (9)

As I understand it, if 18x9.5 +45 will fit the brakes, anything with less offset (+38, +20, +15, etc) will also clear the calipers as the wheel is getting further away. Then you need to start thinking about your fenders

Narfle

iTrader: (16)

17x9.5 +38 will require fender rolling in the front, most likely. That would be considered a more aggressive fitment for the stock body.

lOOkatme

iTrader: (19)

Not sure if it will fit over the brakes, but if you want to run a 255/40/17 tire set up, I recommend going with the 17x10 +38mm rpf1.

KNONFS

iTrader: (14)

Got any close up pics of that configuration? For some reason, I am visualizing that setup as a "stretch tire" look

lOOkatme

iTrader: (19)

For best handling you want to slightly stretch the tire. a good rule of thumb is to run a wheel width slightly wider than your tread width. Most of the 255 extreme sport tires have widths between 9.5-10" wide. perfect for a 10" wide wheel.

Here is one on a s2k.

Narfle

iTrader: (16)

It would be more accurate to say that stretching a tire decreases the damping(and sidewall flex) of that tire, which could have a positive or negative impact on handling.

Increased un-sprung weight from an unnecessarily large wheel is also something to consider. There are a lot of factors at play in stuff like this.

KNONFS

iTrader: (14)

Those do not look stretch at all

I've come to realize that there is a point where the word handling becomes subjective.

lOOkatme

iTrader: (19)

Race teams all set up their tires this way. There is not a single competitve team that does not slightly stretch their tires.

Every 1" of front wheel width is about 1 second of lap time reduction, regardless of the weight penelty. This is coming from Urge designs, and also coming from the michelin tire engineers who set up the porsche cup car.

Basically the recommendation is to run 18" wheels with a slight stretch of the tire. Run the widest wheel you can fit on the car and stretch the tires.

The miata guys, who don't have much power have noticed that the wider wheels drop their lap times, even with a weight penelty.

The theory behind it is with a slight stretch of the sidewalls making a trapezoidal cross section provides the best support of the tire tread/contact patch with the ground, it provides the best steering response, and breakaway characteristics of the tire. A larger tread width than wheel width can create a muffin top, lead to snap oversteer/understeer type scenario's and also reduces the contact patch leading to an inefficient tire/wheel combo.

The order of importance is below.
1) wheel width (wider is better).
2) Wheel Rigidity
3) Weight of set up.

Given the weights are somewhat close and not completely ludacris. Ludacris is a 10lbs+ per wheel/tire set up.

FASTMETABOLISM

17x9.5 +38 fit great. the previous owner of my car was running that size rpf1 no problem with 255 all around. rolled fenders and quaters though. i plan on running 17x10 +38 all around with 255's. it shouldnt be an issue.

and +1 for running a slightly stretched tire. it really does improve the cars handling characteristics

jasonn

iTrader: (10)

That's me! I also believe 17x10 will fit better. On stock front fenders, you might not clear them but with 17x9.5, you'll clear those no problem.

lOOkatme

iTrader: (19)

The tire is in the same location on a +38mm if it is 9.5" or 10" wheel. The 10" wheel will be located around the 9.5" wheel, but the tire will sit in the same exact location, just stretched a little outward on the 10" making it more favorable to handling.


If anything, the 10" is an easier fit because you give yourself a little more room for upgraded brake calipers if you ever decide to go that route.

jasonn

iTrader: (10)

Rpf1 is notorious for crappy brake fitment. Yes, the wheel's center will be at the same spot but I said maybe because it depends on the height. If the compression of the suspension causes the wheels to go up against the fender, its more likely to rub on the 10 since the bead area is moved roughly 6mm outwards.

msilvia

Jasonn, what needed to be done to the front fenders to fit the 17x9.5s? Did you rub at all? Did you track the car? What was your ride height/suspension setup like?

Thanks!

jasonn

iTrader: (10)

It's been a while on the stock fenders but if iirc, the fronts where rolled slightly, rears were not touched, and my front camber was -2. I only had the chance to track it once at Laguna Seca before I switched out fenders and it didn't rub then.

Narfle

iTrader: (16)

People generally run 17x10 +50 to fit on the stock body.
17x10 +38 may require some serious rolling or wide fenders.

lOOkatme

iTrader: (19)

I rolled my fenders and run 2 degrees negative camber. You want the camber anyway for handling, but it does allow you to fit larger tires.


Here is an 18x10 +38 265/35/18 Kumho XS tire on the front of my car. It's not that close to the fender.

Narfle

iTrader: (16)

Yeah, you can see the stretch/roll/camber. Is it riding kindof high there, or just the picture?

Most of the time I see people recommending 285's on 10" wide wheels.
Those 265's are clearly stretched, you can imagine 255 would be even more so. So that helps with fitment.
-2degrees is pretty aggressive for a street car. Not sure what OP's intentions are.

lOOkatme

iTrader: (19)

The front of the car is riding at 25". I will be running much wider here very soon. 285/30/18 on 18x11.5 +41mm effective offset. I might need a small spacer in the back to kick out the rear so I don't hit the trailing arm. We will see when the wheels come this week.

The 265/35/18 is barely stretched on a 10" wheel. the tread width on these tires is about 9.75" or so, so I have a little more wheel width than tread width, which is what you want. a 265/18x10.5" is better for handling. I did this because the 265's were soo cheap when I purchased them.

I have another set of RE-11 in 265/35/18's and the tire bead width in its natural state is 10.1" across. I have a 285/30/18 A048 and the tire bead width is 10.75" across and tread width of 10.9" or so.

Michelin recommends for handling that the tire beads be located at or farther out than the tread width of the tire for better handling and the most optimum handling/breakaway/steering reponse/etc characteristics.

I attached a 18x10.5 +30mm 285/30/18 A048 combo on the front of my car, these were some that I sold, but they are probably a little too aggressive, a +40mm offset would easily fit on the car with a 285/30/18 from my test measurements.

Narfle

iTrader: (16)

Gotta love concave NT03's

lOOkatme

iTrader: (19)

I just test fit my 18x11.5 +41MM effective offset wheels and my math is correct. They clear the stock rear trailing arm on both sides, and in the front they contact one of the coilover springs barely at full lock. I am going to run 285/30/18 RE-11 tires with a tread width of 11 inches.

mvs1

Running Enkei GTC01 17x9.5 38 offset all the way around, 255/40 front and 275/40 rear. Ride height is 25" all corners. Front fenders rolled, rear rolled pretty much flat. Tein Super Street coilovers w/stock rate springs. Stock brakes, no rubbing issues anywhere with room to go inward by another .5" front and 1" rear without issue. Pic's of current set up and race set up with RPF1 17x9 42 offset 255/40's front and 17x9.5 38 offset.

gsx-lex

iTrader: (1)

Does anyone have 17x10 +38 in the front, without rolling the fenders? There is a set available in my area with a 235 tire, and I'd like to it get it, if it will clear the front fender.