235/45R18 vs 225/45R17 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 | 235/45R18 | 225/45R17 | Difference |
|---|---|---|---|
| Overall Diameter | 668.7 mm (26.3") | 634.3 mm (25") | -34.4 mm |
| Section Width | 235 mm (9.3") | 225 mm (8.9") | -10 mm |
| Sidewall Height | 105.8 mm | 101.3 mm | -4.5 mm |
| Circumference | 2100.8 mm | 1992.7 mm | -108.1 mm |
| Revolutions/Mile | 766 | 808 | +42 |
| Aspect Ratio | 45% | 45% | 0% |
| Rim Diameter | 18" | 17" | -1" |
Key Impact Summary
Speedometer Correction Table
When switching from 235/45R18 to 225/45R17, your speedometer will over-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 28.5 mph | -1.5 mph |
| 40 mph | 37.9 mph | -2.1 mph |
| 50 mph | 47.4 mph | -2.6 mph |
| 60 mph | 56.9 mph | -3.1 mph |
| 70 mph | 66.4 mph | -3.6 mph |
| 80 mph | 75.9 mph | -4.1 mph |
| 90 mph | 85.4 mph | -4.6 mph |
| 100 mph | 94.9 mph | -5.1 mph |
| 110 mph | 104.3 mph | -5.7 mph |
| 120 mph | 113.8 mph | -6.2 mph |
What This Swap Means
Narrower tires (225/45R17): The 10mm narrower contact patch reduces rolling resistance, potentially improving fuel economy. Narrower tires also cut through standing water better, reducing hydroplaning risk. However, dry grip and cornering stability may decrease slightly.
Shorter sidewall: The 4.5mm 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: Decreases by 17.2mm, lowering the center of gravity slightly which can improve handling stability.