245/45R18 vs 255/40R19 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 | 245/45R18 | 255/40R19 | Difference |
|---|---|---|---|
| Overall Diameter | 677.7 mm (26.7") | 686.6 mm (27") | +8.9 mm |
| Section Width | 245 mm (9.6") | 255 mm (10") | +10 mm |
| Sidewall Height | 110.3 mm | 102 mm | -8.3 mm |
| Circumference | 2129.1 mm | 2157 mm | +27.9 mm |
| Revolutions/Mile | 756 | 746 | -10 |
| Aspect Ratio | 45% | 40% | -5% |
| Rim Diameter | 18" | 19" | +1" |
Key Impact Summary
Speedometer Correction Table
When switching from 245/45R18 to 255/40R19, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 mph |
| 40 mph | 40.5 mph | +0.5 mph |
| 50 mph | 50.7 mph | +0.7 mph |
| 60 mph | 60.8 mph | +0.8 mph |
| 70 mph | 70.9 mph | +0.9 mph |
| 80 mph | 81.1 mph | +1.1 mph |
| 90 mph | 91.2 mph | +1.2 mph |
| 100 mph | 101.3 mph | +1.3 mph |
| 110 mph | 111.4 mph | +1.4 mph |
| 120 mph | 121.6 mph | +1.6 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.
Shorter sidewall: The 8.3mm 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 4.4mm, providing slightly better approach angles for off-road driving and speed bump clearance.