235/55R17 vs 245/50R18 Side-by-side tire size comparison with specs and compatibility
This tire swap is within the safe 3% diameter threshold. It should not cause issues with speedometer accuracy, ABS, or traction control systems.
Full Specifications Comparison
| Specification | 235/55R17 | 245/50R18 | Difference |
|---|---|---|---|
| Overall Diameter | 690.3 mm (27.2") | 702.2 mm (27.6") | +11.9 mm |
| Section Width | 235 mm (9.3") | 245 mm (9.6") | +10 mm |
| Sidewall Height | 129.3 mm | 122.5 mm | -6.8 mm |
| Circumference | 2168.6 mm | 2206 mm | +37.4 mm |
| Revolutions/Mile | 742 | 730 | -12 |
| Aspect Ratio | 55% | 50% | -5% |
| Rim Diameter | 17" | 18" | +1" |
Key Impact Summary
Speedometer Correction Table
When switching from 235/55R17 to 245/50R18, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 mph |
| 40 mph | 40.7 mph | +0.7 mph |
| 50 mph | 50.9 mph | +0.9 mph |
| 60 mph | 61 mph | +1 mph |
| 70 mph | 71.2 mph | +1.2 mph |
| 80 mph | 81.4 mph | +1.4 mph |
| 90 mph | 91.6 mph | +1.6 mph |
| 100 mph | 101.7 mph | +1.7 mph |
| 110 mph | 111.9 mph | +1.9 mph |
| 120 mph | 122.1 mph | +2.1 mph |
What This Swap Means
Wider tires (245/50R18): The 10mm wider contact patch provides better grip in dry conditions and improved cornering stability. However, wider tires increase rolling resistance slightly, which may affect fuel economy by 1-2%. They are also more susceptible to hydroplaning in wet conditions.
Shorter sidewall: The 6.8mm decrease in sidewall height improves steering response and cornering precision. However, ride quality becomes firmer and the wheels are more vulnerable to pothole damage. This is a common trade-off when upsizing wheels (plus-sizing).
Ground clearance: Increases by 6mm, providing slightly better approach angles for off-road driving and speed bump clearance.