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
Similar diameter does not establish interchangeability. Follow the vehicle manufacturer's approved sizes; see Michelin's tire-size guidance.
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. The 3 percent cutoff is a comparison filter, not a fitment approval. Use vehicle-approved sizes and check rim width, load and speed ratings, and clearances. 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. Actual dimensions depend on the tire model, tread depth, pressure and load; check the tire manufacturer specifications.
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?
Nominal size comparison only: 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. This does not confirm fitment. Check approved rim widths, load and speed ratings, and vehicle clearances. The nominal extra width adds about 0.39 in of clearance on each side of the tire and a rim width that suits 255 mm.