Tire Size Comparison
Compare two tire sizes — width, profile, rim — to see the overall-diameter difference, the percentage change, and a fitment warning when rim sizes differ.
Category: Cars & Vehicles
About this tool
What Is Tire Size Comparison? The Tire Size Comparison takes two tire sizes in width/profile/rim format, computes each overall diameter from sidewall and rim, and reports the difference in millimetres and inches, the percentage change, and a warning whenever the two tires use different rim diameters. How It Works Overall diameter equals the rim diameter (in inches × 25.4) plus twice the sidewall height (width × profile/100). Each tire is reduced to a total millimetre figure; the tool subtracts the two, converts the gap to inches, and expresses it as a percentage of the second tire's diameter. Worked Example Comparing 225/45R17 to 235/40R17, the first has a larger sidewall and a larger overall diameter by roughly 1%. A difference under about 3% is commonly considered acceptable for a speedometer, while more than 3–4% affects gearing and clearance. Common Use Cases check how a slightly taller or wider tire changes ground clearance and speedometer confirm two size options are close enough to swap without recalibrating flag mismatched rim diameters before buying a set Important Notes the percentage is relative to the second (comparison) tire you enter a width or profile change alone does not guarantee the two fit the same rim always verify clearance to suspension, fenders, and brakes before installing Related Tools Tire Size Calculator Tire Pressure Calculator Speed Converter Dista