GarageCalc What 305/70R16 means
305 is the section width in millimeters (12.0 in). 70 is the aspect ratio: the sidewall is 70 percent of the width, so 305 × 0.70 = 214 mm (8.4 in). R is radial construction, and 16 is the wheel diameter in inches (406 mm). Stack two sidewalls on the wheel and you get the overall diameter: 406 + 2 × 214 = 833 mm, or 32.8 in.
A full marking adds a load index and speed rating after the size, for example 305/70R16 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 305/70R16
Going up one wheel size, the closest match is 285/70R17 at -0.3% diameter with a 200 mm sidewall instead of 214 mm. No common 15-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 305/70R16 tire?
32.8 inches (833 mm) in overall diameter: the 16-inch wheel (406 mm) plus two 214 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 305/70R16 in inches?
32.8 x 12.0 R16: 32.8 inches tall, 12.0 inches wide, on a 16-inch wheel. The sidewall is 8.4 inches and the circumference is 103.1 inches, so the tire turns 615 times per mile.
What tire sizes are equivalent to 305/70R16?
Within 3 percent of the same diameter on the same 16-inch wheel: 285/75R16 (+0.1%); on a 17-inch wheel: 285/70R17 (-0.3%), 295/70R17 (+1.4%). The percentage is the diameter change, which is also your speedometer error.