285/55R20 vs 305/55R20Tire Size Comparison
The 2.7% diameter difference is within the accepted 3% tolerance.
Comparison Details
Speedometer Correction
When switching from 285/55R20 to 305/55R20, your speedometer will differ from actual speed.
| Speedometer | Actual Speed | Difference |
|---|---|---|
| 30 km/h | 30.8 km/h | +0.8 km/h |
| 40 km/h | 41.1 km/h | +1.1 km/h |
| 50 km/h | 51.3 km/h | +1.3 km/h |
| 60 km/h | 61.6 km/h | +1.6 km/h |
| 70 km/h | 71.9 km/h | +1.9 km/h |
| 80 km/h | 82.1 km/h | +2.1 km/h |
| 90 km/h | 92.4 km/h | +2.4 km/h |
| 100 km/h | 102.7 km/h | +2.7 km/h |
| 110 km/h | 112.9 km/h | +2.9 km/h |
| 120 km/h | 123.2 km/h | +3.2 km/h |
| 130 km/h | 133.5 km/h | +3.5 km/h |
Individual Tire Size Details
Practical Guidance
Switching from 285/55R20 to 305/55R20 is within the industry-accepted 3% diameter tolerance. Your speedometer, ABS, and traction control should function normally. Both sizes fit the same 20-inch rim, so no wheel change is needed.
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 2.68%, width changes by 20mm.
Speedometer error will be 2.68%. At an indicated 100 km/h, actual speed is about 102.7 km/h.
Ground clearance changes by +11.0mm per side.