Wheel Backspacing

Yeah what kind of backspacing do i need to fit American Racing torque thrust II on my 89 iroc? I'm wanting 17x8 in front and 17x9.5 in the back. It should be 5x 4.75 bolt circle right?

Also What tire size would be the best Fit for that set?

Did you try out tirerack? I seem to recall them having a nifty little "calculator" for situations like this.

Thank you wright.
I never heard of tirerack.

in the back 275/40, front i dont know......go big, go 9.5's all the way around.

For 8 and 9 1/2 inch wheels you can go with as little as 5 inches in the front but I would go 4 1/2. The back needs to be about 5 1/2 but some cars(mine) will work fine with 6 inches. If you want them to have the same outer spacing you would have to go with 4 inches front and 5 1/2 rear. The 18 inch TTII's I am thinking about switching to is a 10 wide wheel and I am going with 4 inches front and 6 inches rear. The tire sizes for 17's (I have 8 inch front and 9 1/2 rear now) are 245/45 R17 and 275/40 R17. Also keep in mind that every car can have slight differences. Mine is riding on Sportline springs and is a bit lower than stock so if I can fit them, a stock springed car shouldn't have any issues.