GarageCalc What 235/75R15 means
235 is the section width in millimeters (9.3 in). 75 is the aspect ratio: the sidewall is 75 percent of the width, so 235 × 0.75 = 176 mm (6.9 in). R is radial construction, and 15 is the wheel diameter in inches (381 mm). Stack two sidewalls on the wheel and you get the overall diameter: 381 + 2 × 176 = 734 mm, or 28.9 in.
A full marking adds a load index and speed rating after the size, for example 235/75R15 91V. Those two codes set how much weight and speed the tire is certified for; look them up in the load index chart and the speed rating chart.
Plus and minus sizing from 235/75R15
Going up one wheel size, the closest match is 235/70R16 at +0.3% diameter with a 165 mm sidewall instead of 176 mm. No common 14-inch size stays within 3 percent either. Anything inside 3 percent keeps the speedometer, ABS and gearing effectively stock; the comparison calculator shows the full speedometer table for any pair.
Frequently asked questions
How tall is a 235/75R15 tire?
28.9 inches (734 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 176 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 235/75R15 in inches?
28.9 x 9.3 R15: 28.9 inches tall, 9.3 inches wide, on a 15-inch wheel. The sidewall is 6.9 inches and the circumference is 90.7 inches, so the tire turns 698 times per mile.
What tire sizes are equivalent to 235/75R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 255/70R15 (+0.6%), 225/75R15 (-2.0%); on a 16-inch wheel: 235/70R16 (+0.3%), 255/65R16 (+0.6%). The percentage is the diameter change, which is also your speedometer error.
Can I use 255/70R15 instead of 235/75R15?
Dimensionally yes: 255/70R15 is 0.6% taller (+5 mm) and 20 mm wider, and at a true 60 mph the speedometer would read 59.6 mph. The extra width needs about 0.39 in of clearance on each side of the tire and a rim width that suits 255 mm.