Wheel size question

[BoxsterInTheSun]

Apologies for the delay, it took a while before I had time to pull the wheels off and check them.

From the looks of it, the rears are marked with 126 55, and the fronts are marked with 124 51, I'm assuming that's what gives the wheels the different sizes?

I now have the wheels back in the original configuration, but now I'm wondering if this is actually a valid setup for this car in the first place ( previous owner put these wheels on ), and maybe this is the root of my steering wheel shake?

[alexc0814]

your fronts are marked 7J17et55 and your rears are 8.5J17et50

fronts == 7 inch wide wheel, 17 inch diameter, and offset of 55

rears == 8.5inch wide wheel 17 inch diameter and offset of 50

boxsters have a staggered setup, so this is normal, I don't see why it would create a steering wheel shake inherently. maybe a bent rim?

[tcoradeschi]

Originally Posted by BoxsterInTheSun

Apologies for the delay, it took a while before I had time to pull the wheels off and check them.

From the looks of it, the rears are marked with 126 55, and the fronts are marked with 124 51, I'm assuming that's what gives the wheels the different sizes?

I now have the wheels back in the original configuration, but now I'm wondering if this is actually a valid setup for this car in the first place ( previous owner put these wheels on ), and maybe this is the root of my steering wheel shake?

So, you have correctly sized wheels - 7x17 front, 8.5x17 rear. You don’t have correctly sized tires on them. Should be something like 205/50x17 front and 255/40x17 rear.

Not saying that has a damn thing to do with the vibration you’re dealing with, but it does explain what you saw when you swapped front for rear.

[BoxsterInTheSun]

Originally Posted by tcoradeschi

So, you have correctly sized wheels - 7x17 front, 8.5x17 rear. You don’t have correctly sized tires on them. Should be something like 205/70x17 front and 255/40x17 rear.

Not saying that has a damn thing to do with the vibration you’re dealing with, but it does explain what you saw when you swapped front for rear.

This is actually super helpful. I was considering getting new tires anyway, just to rule them out as the cause of the vibration ( I think they're cheap ones ). I'll plan to get correctly sized tires and see if that changes anything, regardless, I'm sure it isn't helping the car with the current ones on it.

Thanks again for spotting that. It has had 2 alignments, and 2 wheel balances, both at different places, and nobody noticed.

[997_986]

Originally Posted by tcoradeschi

So, you have correctly sized wheels - 7x17 front, 8.5x17 rear. You don’t have correctly sized tires on them. Should be something like 205/70x17 front and 255/40x17 rear.

Not saying that has a damn thing to do with the vibration you’re dealing with, but it does explain what you saw when you swapped front for rear.

205/50 R17 fronts and 255/40 R17 or 225/45 R17 on the rears

[tcoradeschi]

Originally Posted by 997_986

205/50 R17 fronts and 255/40 R17 or 225/45 R17 on the rears

Good catch! I corrected the typo.

[BoxsterInTheSun]

Originally Posted by 997_986

205/50 R17 fronts and 255/40 R17 or 225/45 R17 on the rears

Thanks so much, this is really helpful. For the rears, are the 2 different sizes just personal preference? What's the difference? Thanks again!