I've got 295/55R15 Mickey Thompson Street ETs on my 15" x 10" steel wheels with 5.5" backspacing. My car's a '68, but I doubt that a '69 is much different. There's sometimes a little rubbing if I turn corners too quickly, but other than that, I haven't had any issues.
Is that with the wheel lips rolled? I just put new quarters on my GTX, just got it out of paint and REALLY don't want to have to roll the new lips...
but with the new engine if I don't run a big tire it's not going to hook at all...so....I will if I have too...
