My POS rear tires are gone on the 89 S4. They were 275/30/18. Can I go all the way to 275/45/18 without a problem??? At this point...better gas mileage is more important than high speed cornering...of which I do none of...any more. I know at 60 miles per hour I will be traveling 65 mph but other than that will there be any other problem? I hope it would help with the ride as well. I must be getting old.

Overall diameter of the 275/35/18 is 25.7" and the 275/45/18 is 27.7" so 2" in diameter larger and 1" on the radius.

 

Uh, actually I'm surprised you fit 275s at all without rolling the fenders. My 265/35/R18s are about 1/2" from the fender lip.

-Sean

 

Depending on the wheel you can fit up to a 295 without any major modifications. My rear fenders aren't pulled, and are only rolled slightly. Though, since it was an S I had a huge spacer to remove and then had to add a small one due to clearance inside the wheel well.

Thee cars just look way better with big rubber out back.

 

Yes...these are reproduction wheels. The rear is 10" wide with either a 47 or 49mm offset ( can't remember ) and the 275 is fine.

I just need to know if I can go TALLER than 30...I would LOVE a 45 if it will fit but the 40 would be an improvement over the 30...both for gas and ride.

 

A 275/45/18 will fit on the rear, but you will be going from a 24.5" diameter to a 27.8" diameter - a 3.3" increase. Actual speed will be 67.9 at an indicated 60 mph (13.2% faster). Of course, you should see improved gas mileage since you'll be going down hill all the time .

The main drawback is that the differential in revolutions per mile will turn off the anti-lock function of your brakes.

I ran a pair of 275/45 Panamera take-offs on the rear of my '89 for a couple of days while I was waiting for my ordered 265/35's to arrive. The anti-lock system was not happy....

By the way, you can't do a similar increase in height on the front because the Panamera 245/50/18 fronts would not even fit in the wheel well. The increase in diameter simply will not physically fit.

James

 

Do you know what the offset is on the Panamera rims you have? Mine are 10" wide with 47 or 49MM offset. I am concerned about the inside forward wheel well rubbing. That looks like the only ??? area. I can live with the speedo and anti lock issue. It will be nice to add a couple MPG.

Thanks for the feedback James

 

The Panamera fronts are 8" ET59, rears are 9" ET53.

James

 

I had NO idea you could put a 275 on a 9" rim.

 

Dean, why don't you go to a 295 30 18? It will fit on a 10" wheel and the diameter is correct at 25" so you'll have a tad bit more sidewall than the 275 30 18.

 

Each tire manufacturer has different tolerances. You need to know the thread width and the total width to see if they fit.