No_Substitute

My fronts are et50 (with 18/225/40 tires) and fit fine. My rears are et47 (with 18/275/35 tires) and very slightly rubbed on the outsides. A couple of tugs on the fenders solved it. Tire shape may be a factor in close cases like that. 285+ would not have fit without some additional fender work.

Ispeed

No disrespect meant, but the definition of "fit fine" will vary depending on where and how you drive.
My definition of "fit fine" is to drive the car as hard as you can on twisty roads with bumps and dips that use up suspension travel; with no rubbing. Florida is pretty flat and straight, and even Mass is not a great place to test stuff either.

No_Substitute

You've obviously never seen the killer curb at the end of my driveway.

Enjoy your wheels. Peace.

Avve

Hi James, but people here tell me that I "need" maximum amount of tire, i.e.285-295 in the back. The width of the rear tires will influnce grip (and lap times)- or??? Since you race 928's you know, but I'm a bit confused.

AO

Dean-

Sorry I didn't respond to you email earlier. The basic rule is, the higher the offset, the further inboard it will be.

REARS: Jon in OZ's theory is spot on - with a 65mm on the rear you can put a spacer on and bring them out as needed. However, I'm pretty sure the 65ET wheels will rub on the inside without any spacer, so I would probably stay away from these if the 47's will fit which I'm pretty sure they do. With 47ET rears (I'm assuming a 275 tire) You should have about 15mm of clearance between the tire and the fender if the fender has the factory rolled lip like on my GT. I had a 47ET wheel and ran a 275 on my old 82, and it just fit.

Fronts: While a 50ET offset will usually work, many have experienced poor handling characteristics with anything less than a 55ET. But they do usually fit, assuming an 8" wheel or less.

This is why the Carrera III wheels are so popular right now. You can get an 8" front with 57ET! and the rears ET's work quite well too ( I forget the ET's). Plus they're available in a 10" or 11" width for the rears!

pcar928fan

The 928 is not a particularly tail happy car. Having good grip front and rear is best. If you don't have enough front tire on the car it will understeer so bad that it won't be fast, relatively. You can help dial a lot of that out by stiffening the rear way bar (ie. adjustable rear drop links), and a different alignment, but still non-staggard tires are a great way to go. If you did 265 frnt/rear or even bigger if they would fit then all the better. An S4 normally has 225 and 245, so if you were to jump up to 265 both that would be nice. The car should feel well balanced on track too.

I used 245 frt on 7.5" D90 GT wheels, and 265 rear on 9" D90 GT wheels and I had a bigger sway bar on the front of the S4 and I would grind the front tires off in 6 20 minute sessions! That gets expensive even if you are only running Kuhmo Victoracers. So I didn't get to drive every session of a weekend and it would cost me $250 in tires alone!

My race car has 12" front and rear wheels and I use slicks on them and because they are the same size and offset I can switch them back to front to make them wear evenly. Of course that is a lot of tire and the race car is 1000# lighter than the S4 with 100 LESS HP, so I can go with one set of used slicks (yea, I buy used slicks at less than $75/tire!) for at least 2 or 3 weekends! AWESOME!

Good luck with whatever you choose to do...

dprantl

For kicks I tried to put my 18x10 ET64mm wheels on the front of my former '86. It stuck out very far and would have absolutely ruined my fenders unless my ride height was super high. It actually looked comical. I suppose if you rolled the crap out of the front fenders it could fit, but it looked to me like it would rub on the insides (both front and back) as well during sharp turns.

Dan
'91 928GT S/C

Dean_Fuller

Thanks guys...I ordered the 47mm rears.

I haven't seen these on anyones 928 yet. Am I the only one that thinks they will look good?

AO

Dean_Fuller

Is adding a 6mm spacer to the fronts a no no??

AO

That's a big no no!

By adding the spacer, you will be effectively reducing your front ET to 44mm. The fronts will stick way out and may quite possibly rub.

If you have them just sitting around, you might be able to use them on the rears to push them out ever so slightly to fill up the wheel well.

Dean_Fuller

Andrew...
I can not open your wheel fitment Excel sheet.. can you post it run with 18" wheels 8" front 10" rears....that I know would help me.
Again the 47mm offset in the rear will work with a 275 tire it sounds like....I wonder if I can squeeze a 285 and still not rub fender.

AO

Here it is, but in my opinion, it's too close to call. There are two main factors that come into play: Variations in the car, and variations in the tire (between mfg.).

You should also check with your tire mfg to see if they recommend putting a 285 on a 10" wheel. Most say max is a 275 for a 10" wheel, but it still can be done. Just letting you know.

P.S. your are highlighted in yellow.

Dean_Fuller

many thanks Andrew.

Dean_Fuller

UPDATE!!!

Ordered tires last night from Tire Rack...235/40-18 fronts and 285/30-18 rears.
Got a call from Gavin at Tire Rack first thing this morning. He wanted to verify the sizes. I gave him my new wheel sizes, offsets and car type. He said he could sell the tires to me in the sizes I ordered but that Tire Rack could not issue me a fitment guarantee. He said the sizes ordered fit 8" and 10" wheels on the narrowest width dims which are not recommended by any of their tire manufacturers. He advised to stay in the middle which would help with handling and minimize sidewall rotation in turns at speed. He stated that the sizes ordered would almost be unsafe with aggressive driving.

Ended up going with 225/40-18 fronts and 265/35-18 rears. These sizes will allow the fitment guarantee to be issued.

I just thought I'd pass this along if people feel they are lacking handling with the wider tires...may have something to do with this wheel width min / max stuff.