ok i am lookin at a set of american racing wheels.i have a 86 iroc and i am wanting to go with 17X9 in the front and 18X9 in the rear. what would be the ideal offset and backspacing for these wheels on my car?

 

5.5" backspace in front, and 5" bs rear.
You may want to consider 8" wide rims up front as wider rim/tires don't fit that great (will rub near steering locks).
If you go with an 8" up front rim use 4.5" backspace

 

the wheels that i am looking at shows they only come like with these specs for 5 on 4 3/4 bolt pattern:

17X8 - 5 7/8" B.S
18X8.5 - 6 1/8" B.S

i am also lookin at another set that would be my second choice the specs on them are:

17X7.5 - 5 3/4" B.S
18X9 - 6" B.S

would either of these wheels work or am i going to have an problems with them as far a direct bolt on? thanks in advance for any help!!

 

Anything different that what I posted will pretty much require a spacer
17x8 front with 5 7/8 needs 1 1/8 spacer
18x 8.5 rear with 6 1/8"bs will need 1 5/8" spacer
other ones need spacers too

 

ok thanks for clearing that up for me! where can i get these spacers at and how much are they?

 

The technical term is actually adapter.
A spacer is really only good for max 1/4" because of thread engagement. An adapter will bolt to your hub and has another set of bolts that your wheel will bolt to. Go to skulte.com, that's the best place to get them. You can also learn about backspacing and adapters on his site.