Tire size confusion... 1989 S4
 

OK, wheels are on their way and wanting to order tires for them so as to eleviate downtime..

Wheels are:
Front: 18 x 7.5 50 offset
Rear: 18x10 Offset 65

According to the spreadsheet Andrew Olson created at

http://members.rennlist.com/andrewmo...01-24-2008.xls

I will need to put a 15mm spacer on the rears and then the correesponding tire sizes should be:

Front: 225/45/18
Rear: 295/30/18

BUT.. in between being referred to the spreadsheet by someone here I had emailed TireRack, they replied:

"The tire sizes we recommend for these wheels are 225/40 18 front and 265/35 18 rear. Anything wider than 265 on the rear will most likely require fender modification, otherwise it will rub ."

I did tell them the year, model, etc. and have used TireRack numerous times in the past but am concerned over the large disparity in recommendations on tire sizes.

Thoughts?

Tire Rack is always overly conservative in their estimates.

Go with Andrew's recommendation.

I think you mean 225/40-18 in front...that will fit

Just about anything will fit in the rear....from 255 up to the 295....however I think if you run the spacer in the rear you WILL have to roll the fender...without it, you might be okay

Fronts: should be 225/40 instead of 225/45 (some people fit 235 without problems)

Rears: I don't think they will rub the fender, but if you have an original muffler, the inside wall could rub on the muffler.

Andrews spreadsheet shows for the front: Spacer: 0 Width: 7.5 Offset: 50 Tire Size: 225 45 18

For the rear the spacer cell was set to 0 for the rear and in the field which says FITS!/STICKS OUT/RUBS/Etc. it says "RUBS INSIDE!" if leave spacer field at 0. If change spacer field to 15 it says "FITS!". Was I wrong in inputting 15 for the spacer?

Muffler is original... and really not interested in rolling the fender...

So, based on the above replies should go with

FRONT: 225/40/18
REAR: ????

Wanting to order the tires today so they will arrive close to when the wheels do...

On my '89 with the original muffler I have 285/30/18. I have about 10 mm between the outside wall and the fender and 10 mm between inside wall and the muffler. But my ET is 58 versus your 65. That means your tire sits 7 mm more inside than mine. So theoretically a 7 mm spacer should work, but please note I'm not familiar with spacers and don't even know if a 7 mm exists. So from a dimension standpoint 285/30/18 should work, but with the correct spacer. Maybe maybe 295/30 will work, but it would be really cutting it close.

I question the wisdom of wanting a 225 on the front and a 295 on the rear.

The 928 understeers enough in stock configuration!

You want wider tires on the front if you go with 295 on the rear.

I'm running 245 front and 275 rear on my GTS. Cornering and balance is greatly improved.

I generally do not recommend 295's on a 10" rim. Especially on an S4/GT unless you're willing to flare the fenders. Instead a 275 or 285 should work just fine.

Randy, I think you mean UNDERsteers enough in stock config.

I have on my S w/o Spacers 285 tires and a 10" rim ET65. It is VERY tight on the inside w/ about 8mm on the outside. Can't say how that compares to an S4... Randy is correct and having tires more closely sized front to rear is better than a big stagger front to rear!

For the rears I start with what I have on my 17 by 9 inch wheels with 47 offset. They give me about a half inch clearance from the tire to the fender flange on my S87 S4. I use 255 40 17 tires on the rear.

With your new wheels you are going to 65 offset with a one inch wider wheel. That means that outside of the center line you have a half inch more width or about 12 mm. The wider offset of 65 puts the wheel about 3/4 inch (18mm) further inside the wheel well. About a half inch of that offset is taken up by the extra width, so without a spacer, your wheels/tires will be about 3/4 inch from the fender flange on an S4.

The next consideration is the outside diameter you are looking for. I think you need to stay in the range of 25 to 26 inches for the rear. Since 10 inches of width is 254 mm, when you add some for the flare of the tire, you should be looking for about a 275 width tire. Since you have 18 inches of wheel diameter, and you are looking for less than 26 inches, you need a percentage profile of the width that will give you that.

With a 265 width, a 40 percent profile will give you two times about 106 mm or 8.35 inches. When added to the wheel diameter you will end up with 26.35 overall diameter. I think that is a little too tall.

A 265 by 35 will give you 25.3 overall height. That is pretty good, but I think you really want a slightly wider tire. Lets look at a 275 by 35. That give you 25.58 overall diameter which I think is just about ideal. Also I think that will put the tire about 3/4 inches from the fender flange on an S4.

What you will need to do is move the wheel/tire assembly out closer to the fender flange. I think you will need a spacer of about 10 to 12 mm. Fifteen, as you anticipated will also probably work. Therefore, the answer is 275 35 18 rears. Good hunting.

Jerry Feather

285 30 18 will be about 24.73 inches tall. I think that is too short for the rear. JF

285/30/18 is as close as it gets to the original 245/45/16, just 3.92 mm larger circumference or 0,21%.

275/35/18 is 68.77 mm larger in circumference, or 3,64%.

That is, if you want to keep as close to stock as possible and keep the speedo accurate (or as close to how "accurate" it was in the first place :)).

My post from your wheels thread:

IMO, 18" (& 19") wheels are unique as you do not need spacers to clear the rear suspension links... as they fit inside of the wheel's inner diameter.

For 17" (and smaller) wheels, spacers are a definite requirement since the rear suspension link will want to make contact with the sidewall of the tire. The spacer would prevent contact (different width spacer depending on wheel/tire combo).

At the beginning, I had Bridgestone RE050's and got minor sidewall scuffing when hitting potholes & such, because those tires had a wheel protecting ridge built into the tire's sidewall -so I used the 'baseball bat' method to slightly flare out the quarters. Once I went to the Michelin PS2's and then Hankook Ventus -I found the flare was not necessary... even though the tires were the "same" size.

Tire construction is as important as the basic "size" when clearance issues apply. Some local RListers may allow you to 'borrow' their wheels & tires for trial fitment... and then go from there.

[QUOTE=pcar928fan;8320468]Randy, I think you mean UNDERsteers enough in stock config.
QUOTE]

yeah, yeah.

OK! Off to shop tires in sizes:

Front: 235/40/18 and Rear: 275/30/18 and will try 10, 12 and 15 mm spacers to see which is the best fit. Tires I am looking at are Hankook Ventus V12 evo K110, had them before on my 2006 911 and 1990 300ZX TT and liked the combination of ride, wear and price.

Unless hear any dissenting advice!

THANKS GUYS! Can't wait to get it rolling and meet the locals in a week or so!

EDIT...

Forgot to ask, will I need to get different sized lugs or what not? Should the spacers be hub centric?

Lord, another edit to fix my typo errors.. fixed sizes above (copied and pasted and failed to correct).. Gonna need that beer tonight after work!