255/45R20 vs 275/40R21Tire Size Comparison
The 2.2% diameter difference is within the accepted 3% tolerance.
Comparison Details
Speedometer Correction
When switching from 255/45R20 to 275/40R21, your speedometer will differ from actual speed.
| Speedometer | Actual Speed | Difference |
|---|---|---|
| 30 km/h | 30.6 km/h | +0.6 km/h |
| 40 km/h | 40.9 km/h | +0.9 km/h |
| 50 km/h | 51.1 km/h | +1.1 km/h |
| 60 km/h | 61.3 km/h | +1.3 km/h |
| 70 km/h | 71.5 km/h | +1.5 km/h |
| 80 km/h | 81.7 km/h | +1.7 km/h |
| 90 km/h | 91.9 km/h | +1.9 km/h |
| 100 km/h | 102.2 km/h | +2.2 km/h |
| 110 km/h | 112.4 km/h | +2.4 km/h |
| 120 km/h | 122.6 km/h | +2.6 km/h |
| 130 km/h | 132.8 km/h | +2.8 km/h |
Vehicles Using These Sizes
Vehicles with 255/45R20
Vehicles with 275/40R21
Individual Tire Size Details
Practical Guidance
Switching from 255/45R20 to 275/40R21 is within the industry-accepted 3% diameter tolerance. Your speedometer, ABS, and traction control should function normally. Note: these sizes require different rim diameters (20" vs 21"), so you will need different wheels.
The 3% diameter tolerance is a widely accepted industry guideline referenced by the ETRTO and most vehicle manufacturers. When in doubt, consult your vehicle's owner's manual or a qualified tire professional. For U.S. tire safety standards and recalls, see the NHTSA Tire Safety page.
Frequently Asked Questions
Safe. The overall diameter differs by 2.16%, width changes by 20mm.
Speedometer error will be 2.16%. At an indicated 100 km/h, actual speed is about 102.2 km/h.
Ground clearance changes by +7.9mm per side.