225/45R18 vs 235/40R18Tire Size Comparison
The 2.2% diameter difference is within the accepted 3% tolerance.
Comparison Details
Speedometer Correction
When switching from 225/45R18 to 235/40R18, your speedometer will differ from actual speed.
| Speedometer | Actual Speed | Difference |
|---|---|---|
| 30 km/h | 29.3 km/h | -0.7 km/h |
| 40 km/h | 39.1 km/h | -0.9 km/h |
| 50 km/h | 48.9 km/h | -1.1 km/h |
| 60 km/h | 58.7 km/h | -1.3 km/h |
| 70 km/h | 68.5 km/h | -1.5 km/h |
| 80 km/h | 78.2 km/h | -1.8 km/h |
| 90 km/h | 88.0 km/h | -2.0 km/h |
| 100 km/h | 97.8 km/h | -2.2 km/h |
| 110 km/h | 107.6 km/h | -2.4 km/h |
| 120 km/h | 117.4 km/h | -2.6 km/h |
| 130 km/h | 127.1 km/h | -2.9 km/h |
Vehicles Using These Sizes
Vehicles with 225/45R18
Vehicles with 235/40R18
Individual Tire Size Details
Practical Guidance
Switching from 225/45R18 to 235/40R18 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 -2.20%, width changes by 10mm.
Speedometer error will be -2.20%. At an indicated 100 km/h, actual speed is about 97.8 km/h.
Ground clearance changes by -7.2mm per side.