Tire Size Calculator

P = Passenger vehicle. 225 = section width in millimeters. 45 = aspect ratio (sidewall height is 45% of width). R = Radial construction. 17 = rim diameter in inches.

The aspect ratio is the ratio of the tire's sidewall height to its width, expressed as a percentage. A 45 aspect ratio means the sidewall height is 45% of the 225mm width, which equals about 101mm.

Overall diameter affects speedometer accuracy, odometer readings, and gear ratios. Using tires significantly different from the OEM size can make your speedometer inaccurate.

Plus-one means going up one inch in rim diameter while reducing the aspect ratio to maintain a similar overall diameter. For example, P225/55R16 to P225/50R17. This improves handling but may slightly reduce ride comfort.

The load index is a number indicating the maximum weight the tire can support (e.g., 91 = 1,356 lbs). The speed rating is a letter indicating the maximum sustained speed (e.g., V = 149 mph).

P-metric tires (starting with P) are for passenger vehicles. LT tires are for light trucks and have higher load ratings and stiffer sidewalls. Using LT tires on a passenger car can result in a harsher ride.