GarageCalc What 175/65R15 means
175 is the section width in millimeters (6.9 in). 65 is the aspect ratio: the sidewall is 65 percent of the width, so 175 × 0.65 = 114 mm (4.5 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 × 114 = 609 mm, or 24.0 in.
A full marking adds a load index and speed rating after the size, for example 175/65R15 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 175/65R15
Going up one wheel size, the closest match is 185/55R16 at +0.2% diameter with a 102 mm sidewall instead of 114 mm. Going down one size, 195/65R14 is +0.1% with a taller 127 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 175/65R15 tire?
24.0 inches (609 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 114 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 175/65R15 in inches?
24.0 x 6.9 R15: 24.0 inches tall, 6.9 inches wide, on a 15-inch wheel. The sidewall is 4.5 inches and the circumference is 75.3 inches, so the tire turns 842 times per mile.
What tire sizes are equivalent to 175/65R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 185/60R15 (-0.9%), 195/60R15 (+1.1%), 165/65R15 (-2.1%); on a 16-inch wheel: 185/55R16 (+0.2%), 195/50R16 (-1.2%); on a 14-inch wheel: 195/65R14 (+0.1%), 185/70R14 (+1.0%). The percentage is the diameter change, which is also your speedometer error.
Can I use 185/60R15 instead of 175/65R15?
Dimensionally yes: 185/60R15 is 0.9% shorter (-6 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 60.5 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 185 mm.