235/55R17 vs 245/50R18Tire Size Comparison
The 1.7% diameter difference is within the accepted 3% tolerance.
Comparison Details
Speedometer Correction
When switching from 235/55R17 to 245/50R18, your speedometer will differ from actual speed.
| Speedometer | Actual Speed | Difference |
|---|---|---|
| 30 km/h | 30.5 km/h | +0.5 km/h |
| 40 km/h | 40.7 km/h | +0.7 km/h |
| 50 km/h | 50.9 km/h | +0.9 km/h |
| 60 km/h | 61.0 km/h | +1.0 km/h |
| 70 km/h | 71.2 km/h | +1.2 km/h |
| 80 km/h | 81.4 km/h | +1.4 km/h |
| 90 km/h | 91.6 km/h | +1.6 km/h |
| 100 km/h | 101.7 km/h | +1.7 km/h |
| 110 km/h | 111.9 km/h | +1.9 km/h |
| 120 km/h | 122.1 km/h | +2.1 km/h |
| 130 km/h | 132.2 km/h | +2.2 km/h |
Vehicles Using These Sizes
Vehicles with 235/55R17
Vehicles with 245/50R18
Individual Tire Size Details
Practical Guidance
Switching from 235/55R17 to 245/50R18 is within the industry-accepted 3% diameter tolerance. Your speedometer, ABS, and traction control should function normally. Note: these sizes require different rim diameters (17" vs 18"), 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 1.72%, width changes by 10mm.
Speedometer error will be 1.72%. At an indicated 100 km/h, actual speed is about 101.7 km/h.
Ground clearance changes by +6.0mm per side.