225/50R17 vs 235/50R18 Side-by-side tire size comparison with specs and compatibility
This tire swap exceeds 5% diameter difference. Not recommended without suspension modifications. Will significantly affect speedometer, ABS, and may cause rubbing.
Full Specifications Comparison
| Specification | 225/50R17 | 235/50R18 | Difference |
|---|---|---|---|
| Overall Diameter | 656.8 mm (25.9") | 692.2 mm (27.3") | +35.4 mm |
| Section Width | 225 mm (8.9") | 235 mm (9.3") | +10 mm |
| Sidewall Height | 112.5 mm | 117.5 mm | +5 mm |
| Circumference | 2063.4 mm | 2174.6 mm | +111.2 mm |
| Revolutions/Mile | 780 | 740 | -40 |
| Aspect Ratio | 50% | 50% | 0% |
| Rim Diameter | 17" | 18" | +1" |
Key Impact Summary
Speedometer Correction Table
When switching from 225/50R17 to 235/50R18, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 31.6 mph | +1.6 mph |
| 40 mph | 42.2 mph | +2.2 mph |
| 50 mph | 52.7 mph | +2.7 mph |
| 60 mph | 63.2 mph | +3.2 mph |
| 70 mph | 73.8 mph | +3.8 mph |
| 80 mph | 84.3 mph | +4.3 mph |
| 90 mph | 94.9 mph | +4.9 mph |
| 100 mph | 105.4 mph | +5.4 mph |
| 110 mph | 115.9 mph | +5.9 mph |
| 120 mph | 126.5 mph | +6.5 mph |
What This Swap Means
Wider tires (235/50R18): 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.
Taller sidewall: The 5.0mm increase in sidewall height provides a more comfortable ride by absorbing more road imperfections. Taller sidewalls also offer better protection against pothole damage to wheels. The trade-off is slightly less responsive steering feel.
Ground clearance: Increases by 17.7mm, providing slightly better approach angles for off-road driving and speed bump clearance.