GarageCalc What 195/55R15 means
195 is the section width in millimeters (7.7 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 195 × 0.55 = 107 mm (4.2 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 × 107 = 596 mm, or 23.4 in.
A full marking adds a load index and speed rating after the size, for example 195/55R15 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 195/55R15
Going up one wheel size, the closest match is 185/50R16 at -0.7% diameter with a 93 mm sidewall instead of 107 mm. Going down one size, 185/65R14 is +0.1% with a taller 120 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 195/55R15 tire?
23.4 inches (596 mm) in overall diameter: the 15-inch wheel (381 mm) plus two 107 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 195/55R15 in inches?
23.4 x 7.7 R15: 23.4 inches tall, 7.7 inches wide, on a 15-inch wheel. The sidewall is 4.2 inches and the circumference is 73.7 inches, so the tire turns 860 times per mile.
What tire sizes are equivalent to 195/55R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 175/60R15 (-0.8%), 185/60R15 (+1.3%), 205/50R15 (-1.6%); on a 16-inch wheel: 185/50R16 (-0.7%), 205/45R16 (-0.8%); on a 14-inch wheel: 185/65R14 (+0.1%), 175/70R14 (+0.9%). The percentage is the diameter change, which is also your speedometer error.
Can I use 205/50R15 instead of 195/55R15?
Dimensionally yes: 205/50R15 is 1.6% shorter (-10 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 61.0 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 205 mm.