GarageCalc What 225/75R15 means
225 is the section width in millimeters (8.9 in). 75 is the aspect ratio: the sidewall is 75 percent of the width, so 225 × 0.75 = 169 mm (6.6 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 × 169 = 719 mm, or 28.3 in.
A full marking adds a load index and speed rating after the size, for example 225/75R15 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 225/75R15
Going up one wheel size, the closest match is 225/70R16 at +0.4% diameter with a 158 mm sidewall instead of 169 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 225/75R15 tire?
28.3 inches (719 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 169 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 225/75R15 in inches?
28.3 x 8.9 R15: 28.3 inches tall, 8.9 inches wide, on a 15-inch wheel. The sidewall is 6.6 inches and the circumference is 88.9 inches, so the tire turns 713 times per mile.
What tire sizes are equivalent to 225/75R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 235/70R15 (-1.2%), 215/75R15 (-2.1%), 235/75R15 (+2.1%); on a 16-inch wheel: 225/70R16 (+0.4%), 235/65R16 (-0.9%). The percentage is the diameter change, which is also your speedometer error.
Can I use 235/70R15 instead of 225/75R15?
Dimensionally yes: 235/70R15 is 1.2% shorter (-9 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 60.7 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 235 mm.