GarageCalc What 205/75R15 means
205 is the section width in millimeters (8.1 in). 75 is the aspect ratio: the sidewall is 75 percent of the width, so 205 × 0.75 = 154 mm (6.1 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 × 154 = 689 mm, or 27.1 in.
A full marking adds a load index and speed rating after the size, for example 205/75R15 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 205/75R15
Going up one wheel size, the closest match is 215/65R16 at -0.4% diameter with a 140 mm sidewall instead of 154 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 205/75R15 tire?
27.1 inches (689 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 154 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 205/75R15 in inches?
27.1 x 8.1 R15: 27.1 inches tall, 8.1 inches wide, on a 15-inch wheel. The sidewall is 6.1 inches and the circumference is 85.2 inches, so the tire turns 744 times per mile.
What tire sizes are equivalent to 205/75R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 215/70R15 (-0.9%), 225/70R15 (+1.1%), 215/75R15 (+2.2%); on a 16-inch wheel: 215/65R16 (-0.4%), 225/65R16 (+1.5%). The percentage is the diameter change, which is also your speedometer error.
Can I use 215/70R15 instead of 205/75R15?
Dimensionally yes: 215/70R15 is 0.9% shorter (-7 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 60.6 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 215 mm.