Tire Size Calculator

A tire size like 225/45R17 means: 225 = section width in millimetres, 45 = aspect ratio (sidewall height as % of width), R = radial construction, 17 = rim diameter in inches. Sidewall height = width × aspect ratio / 100. For 225/45: sidewall = 225 × 0.45 = 101.25mm. Overall diameter = (2 × sidewall) + (rim diameter × 25.4).

Most countries allow ±2.5–4% speedometer tolerance from the factory. A speedometer error of less than 3% from a tire size change is generally considered safe and acceptable. However, larger errors affect odometer readings (affecting warranty mileage and oil change intervals), GPS accuracy comparisons, and can technically cause you to speed without realising it. Errors over 5% should be corrected with a speedometer recalibration.

Plus sizing means increasing the rim diameter while decreasing the sidewall height to keep overall diameter the same (or very close). For example, going from 215/60R16 to 225/50R17 — the rim is 1 inch larger but the shorter sidewall compensates. Benefits include sharper handling and aesthetics. Downsides include less ride comfort and more vulnerability to pothole damage.

Wider tires improve grip and appearance but require sufficient clearance in the wheel well. Generally, you can safely go up 10–20mm in width from the OEM size without rubbing. Always verify clearance at full steering lock and with suspension compressed. Check with a tire fitment guide or ask a tire shop to confirm compatibility for your specific vehicle.