tire size question
 

I have RUF speedline 17's. I will need new tires soon and before I buy, I would like to make sure that I have the right size tires currently on the car. So should I keep the same size tires or go a bit bigger?

Front: 235/45/17
Rear: 255/40/17

Thanks,
Steve

You are in the best position to determine what you need for the next set

You have a fairly nicely sized wheel/tire package now,
Are you happy w/ the cars handling now?
How much room is there to go larger?
If you wanted to change the cars behavoir in any way what would you want different?

Well I have only owned the car for 3 weeks. So it is hard to say. I am quite pleased with the handling thus far. I have not had a chance to really drive it hard. If I track the car it will be very little. Maybe once or twice a year.

The fronts are a bit taller than you rears. Might look at 40's or go to 275's in the back if you have the width.

I defer to the experts.

Then as long as everything is comfortably working now, might as well stay w/ the sizes you have.

common fitments w/ that size wheel are
225/45 & 255/40
235/45 & 255/40
235/40 & 255/40
235/45 & 265/40
235/40 & 265/35 (very hard to find these days)
235/45 & 275/40
235/40 & 275/40
245/40 & 275/40

the bigger the tires get the harder it is to fit them w/o rubbing and yoiu get little to no benefit for street use.

I think the RUF 930 rims are 8&10's.

225's are perfect on 8's and 8's can run up to 245's and work well.

I am not a big fan of tires taller than 25" up front or that are taller in the front than the rear. This puts the front A arms at a less than ideal angle if lowered to near euro height. Ok for looks but it puts the front suspension at a point where the front will lose camber much faster as the car leans than the special 930 back end dose. Also, with tall tires, if set at euro height on stock springs it also dose not leave a lot of front suspension travel.

The 10's fit 275's well. They are about .6" wider and taller than the 255's you are running. I like 255's and 10's are the biggest rims they will fit on. On 10's they will come in a little under there 25" spec'd height. Thus, you would be about .6" taller in front if you stay with your current set up.

Most turbo owners I suspect are putting out a lot of power and would tend to lean toward the 275's as a first choice. They do require about an addational .3" side tire to fender clearance. If it helps the 275's are the same height as the 235/45's you are running. If you run the 235/45's I would not go lower than euro height and might go .25" + higher.

A max tire set up would be 245/275 on your rims if you have the offset or room for it.

You should confirm this with Bill or someone else that knows these cars. :)

I recently found out that my new 993 cup wheels that i'm doing won't be permitted in my region for DE's with adapters or spacers of 1/2"or more. Mine are 2" in the rear, 1" in the front. I guess they will be street wheels. Currently, I have 7/8's with 225's f&r. If I want to go with 245's on the rear it looks like you can fit them on the 8's? Is that correct? If I do that will I need some type of spacer to accomodate the 245's on an 8" wheel or if I get a set of 9"(930 wheels) with a 245 will I need any spacing to fit them. I have an 85' Carrera.

Big spacers are an issue, the factory had to get special dispensation from TUV to run the one on the 930s.

as long as you have reasonable clearance for 225/50 on 8s 245/45 will still fit comfortably

I would much rather have the 245/45 on a 9 than an 8.

I'm looking for the best option. If I can comfortably use my 8's my problem is solved without buying another set of wheels. So, are you saying that I would need a spacer with the 9's on my car or is it just an issue on the 930's?

a 9x16 Fuch(ET15) using 245/45 fits an SC/Carrera rear flare very nicely w/o using any spacers(though some use a very small one). If it were on a 930 then, yes, a largish spacer is needed, if it's on an SC/Carrera chassis w/ 930 flares than an even bigger spacer is needed.