X33RS, what size tire would that be to get the good mileage without over revving... Danny
If your looking for a 28" tire there are only a couple options that I know of that may or may not fit.
A 275-60-15 is 28" and usually what I'll run on the back of most cars, but it's a tight fit on a 69 camaro and would likely rub unless you got fancy with backspacing and rim width.
Another option would be a 235-70-15 which is 27.9" tall and doesn't have near the width of the 275's, so these would be a much easier fit on the rear with stock wheels.
If you want to go more then BFG makes a 255-70-15 which is 29" tall. Depending on the car I sometimes mount these tires on extra wheels and can quickly toss them on for a long highway trip. That way most of the time your regular size tires stay on the car.
Keep in mind an inch added to rear tire height only knocks about ~150-200 rpm off the cruise rpm. It's not a big change unless you're running 26" tires.
I generally run a 255-60-15 on the back of a 69 camaro which fits snug and fills the wheel wells nicely. These are 27" tall. With 3.73's I'll turn 3,000 rpm to go 65 mph. I've criss crossed the country cruising like this without complaint but could knock that cruise rpm down to 26-2700 with the 255-70's tossed on.