Like to know what are the widest tires I can put on the s4 with the 17" cup one wheels.

7.5 front
9.0 Rear.
Thankyou.

 

I run 235 and 275 in the proper aspect ratio (I think 40 and 45...)

 

+1 on the above - 247/40 rear & 235/45 front. Bring my speedo a bit closer to reading right (digital dash is 3% high at open rd speeds).

 

I just want to add that although the 235/45 ratio is mathmatically correct in keeping the correct sidwall height, when paired with the 275/40/17 for the rear, the 45 percent aspect ratio on the front tires looks like they are a taller tire in the front vs the rear even though they are not. It's some kind of optical illusion I guess. So I switched to 235/40/17 in the front and it looks much better in my opinion when paired with the aforementioned 275/40/17's for the rear......

 

Mike, why do you want to go with wider tires?

The stock tire sizes for those wheels were 225/45-17 front, 255/40-17 rears.

You can go larger, but that starts to compromise handling in my view-- especially if the rears get proportionally larger than the fronts-- which increases understeer. When you get to 275/40, the tread width is significantly wider than the rim width-- not the ideal situation.

 

Mike,

Jim is right in that the section width will be over 10.8 inches for the rear tires on a 9" rim. I can say from experience that the 275's on the 9" rim have not caused me any weird handling anomolies. I originally changed to the wider tires for the "look" but now need all the rubber I can get out back for straight line traction.

Just remember that the first number is always the section width in millimeters. So, 275mm divided by 25.4mm per inch =10.826 inches. This number should be from sidewall to side wall and does not accurately express how much actual tread is on the ground because this varies from tire to tire.

The second number is apect ratio; this determines the overall height of the tire in relation to the width. In the back tires case, this is 40 percent. So take the 275mm x 40%=110 millimeters. This is for one sidewall say at the bottom of the tire, so you have to multiply this by 2 sidewalls. So, 110mm X 2 = 220 mm

Take 220mm and divide again by 25.4mm and you get 8.66 inches.

Now add the 8.66 inches to the last number in your tire size which in this case is 17 inches and you get the overall tire height which is 25.66 inches.

Since the S4 (both of the cars in your sig ar S4's) came stock with 16" wheels with 245/45/16 tires, the 275/40/17 tires will be almost exactly 1" taller, which will throw your speedometer off by about 5-6 miles per hour to slow.....

 

Jim, you are also correct for road racing conditions for a regular 928 where rear wheel traction under accel is not a real issue. If you want nice neutral handling you should go REALLY OLD SCHOOL, like the first 928's and match the front and rear tire width...it makes for a better balanced car...

 

I haven't made a decision yet.
I do wish to fill in the space between the tire and the fenders though. Curious about the look.
The GTS is my vehicular Holy Grail but Attys prevent that for now.
From what I 've seen, some have come up with the perfect combination of wheel well -to tire proportions.
I'm not Hannu Mikola by driving style in any means, but I do appreciate the filled in look.

From my readings on this good Forum, there may be a tad trade off to balance (with agressive driving)
I've gotten older and I've slowed down. So balance and subtleties may not be so specifically needed.
Thankyou very-much for your input.