68 camaro wheel questions

[brgable]

man this isn't sounding very good...lol. most 67's and 68's I've seen have 9.5" but I have seen some with 10" on there without a minitub I just didn't get the wheel dimensions from them. the 67 I saw with 11" wheels with that size backspacing were 17" wheels how much of a difference is that from an 18? the wheels i have on it now are 15x8 with 275/60/15 tires with a 1" spacer and the 11" wheels i saw looked to sit in the same spot in the fender well as the wheels on my car now. I will not be lowering the car because I like the car to have some space between the tired and fender plus I am running super comp hooker headers that already hang low enough with stock height springs under the car. my car has the stock 5 leaf springs on the rear to give you and idea of the ride height now. sorry to ask so many questions or sound repetitive but it really helps hearing from people in the know before I go out and spend a lot of money on wheels and tires that don't fit well at all. again, thanks for the help guys!