GarageCalc What 175/50R15 means
175 is the section width in millimeters (6.9 in). 50 is the aspect ratio: the sidewall is 50 percent of the width, so 175 × 0.50 = 88 mm (3.4 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 × 88 = 556 mm, or 21.9 in.
A full marking adds a load index and speed rating after the size, for example 175/50R15 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 175/50R15
No common 16-inch size stays within 3 percent of 21.9 in. Going down one size, 155/65R14 is +0.2% with a taller 101 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 175/50R15 tire?
21.9 inches (556 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 88 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 175/50R15 in inches?
21.9 x 6.9 R15: 21.9 inches tall, 6.9 inches wide, on a 15-inch wheel. The sidewall is 3.4 inches and the circumference is 68.8 inches, so the tire turns 921 times per mile.
What tire sizes are equivalent to 175/50R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 155/60R15 (+2.0%); on a 14-inch wheel: 155/65R14 (+0.2%), 165/60R14 (-0.4%). The percentage is the diameter change, which is also your speedometer error.