Sidewall height is the given % of sidewall width.
I have the 325/50 15 on 15 x 9.5 wheels with 4 inch backspace. The driver side on my car had an extra hunk of fiberglass on the inner wheel well that I had to fix so the tire didn't rub. The passenger side has plenty of clearance. I would like to see the wheels wider and the tires inward about another .5 inches.
I don't think I'd want a tire that's taller. At a time I thought my tires were 27 inches tall because I was measuring them on the car, but I recently removed the tires. They are in fact real close to 28 inches tall. A 315/60 15 of 30 inches tall would look a bit off in my opinion.
I have a 3.73 rear gear.
Tire chart
http://www.mickeythompsontires.com/s...ETStreetRadial