245/40R18 vs 255/40R19 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 | 245/40R18 | 255/40R19 | Difference |
|---|---|---|---|
| Overall Diameter | 653.2 mm (25.7") | 686.6 mm (27") | +33.4 mm |
| Section Width | 245 mm (9.6") | 255 mm (10") | +10 mm |
| Sidewall Height | 98 mm | 102 mm | +4 mm |
| Circumference | 2052.1 mm | 2157 mm | +104.9 mm |
| Revolutions/Mile | 784 | 746 | -38 |
| Aspect Ratio | 40% | 40% | 0% |
| Rim Diameter | 18" | 19" | +1" |
Key Impact Summary
Speedometer Correction Table
When switching from 245/40R18 to 255/40R19, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 31.5 mph | +1.5 mph |
| 40 mph | 42 mph | +2 mph |
| 50 mph | 52.6 mph | +2.6 mph |
| 60 mph | 63.1 mph | +3.1 mph |
| 70 mph | 73.6 mph | +3.6 mph |
| 80 mph | 84.1 mph | +4.1 mph |
| 90 mph | 94.6 mph | +4.6 mph |
| 100 mph | 105.1 mph | +5.1 mph |
| 110 mph | 115.6 mph | +5.6 mph |
| 120 mph | 126.1 mph | +6.1 mph |
What This Swap Means
Wider tires (255/40R19): 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 4.0mm 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 16.7mm, providing slightly better approach angles for off-road driving and speed bump clearance.