GarageCalc What 205/70R15 means
205 is the section width in millimeters (8.1 in). 70 is the aspect ratio: the sidewall is 70 percent of the width, so 205 × 0.70 = 144 mm (5.6 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 × 144 = 668 mm, or 26.3 in.
A full marking adds a load index and speed rating after the size, for example 205/70R15 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 205/70R15
Going up one wheel size, the closest match is 215/60R16 at -0.5% diameter with a 129 mm sidewall instead of 144 mm. Going down one size, 215/70R14 is -1.7% with a taller 151 mm sidewall for more comfort and pothole margin. 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 205/70R15 tire?
26.3 inches (668 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 144 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 205/70R15 in inches?
26.3 x 8.1 R15: 26.3 inches tall, 8.1 inches wide, on a 15-inch wheel. The sidewall is 5.6 inches and the circumference is 82.6 inches, so the tire turns 767 times per mile.
What tire sizes are equivalent to 205/70R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 215/65R15 (-1.1%), 195/70R15 (-2.1%), 215/70R15 (+2.1%); on a 16-inch wheel: 215/60R16 (-0.5%), 205/65R16 (+0.7%); on a 14-inch wheel: 215/70R14 (-1.7%). The percentage is the diameter change, which is also your speedometer error.
Can I use 215/65R15 instead of 205/70R15?
Dimensionally yes: 215/65R15 is 1.1% shorter (-8 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 215 mm.