275/40R18 vs 285/40R18Tire Size Comparison
The 1.2% diameter difference is within the accepted 3% tolerance.
Comparison Details
Speedometer Correction
When switching from 275/40R18 to 285/40R18, your speedometer will differ from actual speed.
| Speedometer | Actual Speed | Difference |
|---|---|---|
| 30 km/h | 30.4 km/h | +0.4 km/h |
| 40 km/h | 40.5 km/h | +0.5 km/h |
| 50 km/h | 50.6 km/h | +0.6 km/h |
| 60 km/h | 60.7 km/h | +0.7 km/h |
| 70 km/h | 70.8 km/h | +0.8 km/h |
| 80 km/h | 80.9 km/h | +0.9 km/h |
| 90 km/h | 91.1 km/h | +1.1 km/h |
| 100 km/h | 101.2 km/h | +1.2 km/h |
| 110 km/h | 111.3 km/h | +1.3 km/h |
| 120 km/h | 121.4 km/h | +1.4 km/h |
| 130 km/h | 131.5 km/h | +1.5 km/h |
Individual Tire Size Details
Practical Guidance
Switching from 275/40R18 to 285/40R18 is within the industry-accepted 3% diameter tolerance. Your speedometer, ABS, and traction control should function normally. Both sizes fit the same 18-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 1.18%, width changes by 10mm.
Speedometer error will be 1.18%. At an indicated 100 km/h, actual speed is about 101.2 km/h.
Ground clearance changes by +4.0mm per side.