I need to know how much offset and backspacing etc I'll need to run on 17x9.5" rims with 275/40ZR17 tires. The rims are being made on order so I need the correct measurement. How much backspacing or offset are ya'll with similar rims and tires running out there? What if the rims are 17x9" or 17x8.5"?

BTW, my car is an 88 IROCZ with all stock suspension and drivetrain. Thanks in advance.

 

I have 4th gen Zr1 17x9.5 wheels and the backspaceing is 56mm. I used 2" spacers on all four wheels. That will work with 275/40-17. My wheels weren't specially made like yours though, just reg 4th gen size, Dont know if it helps at all.

 

factory backspacing is 4.35" front and 5" rear.

with a 9.5" rim, you're gonna want to tweak those numbers, or the new rims will stick out 1.5" too much all around

but you are kind of limited by how far you can tweak. I'd guess something like 4.85" front, and 5.5" rear. That will make everything stick out an inch more all around, but _probably_ won't cause any rubbing problems. You might want to post and find out about that though.

A 9 inch wide rim, or an 8.5 inch rim, i'd use factory numbers, or close to it, because you're not gonna see a significant difference in how far they stick out.

 

I was wondering if offset is the same thing as backspacing just measured in a different way. I read somewhere that with 17x9.5" rims I would need 0mm offset. In other words, the wheel's mounting flange should be exactly on its centerline. I don't mind having the wheels sticking out to the lip of the wheel well. In fact, a little less would be better - I don't want the lip chewing up the tire if it goes in that far.

I have another question too for all you guys running extra wide tires. Do your front tires rub the fenders when the wheels are turned to full lock. I'm asking specifically about the outside edge of the tire making contact with the fender or anything else in there.

 

Backspasing and offset are 2 differant things. Offset is the differance between the front and rear's backspacing. Backspacing is the distance from the inside of the wheel, from the back of the lug holes to the edge of the wheel (at 90 degrees). third gen cars have a 16mm offset in the rear (meaning the rear sticks out 16mm more off the axle than the front, and there are 2 diff backspacing for front and rear). As far as my 4th gen wheels go they are 56mm backspacing on all for wheels (so there is no ofsets)