235/40R19 vs 255/35R20 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 | 235/40R19 | 255/35R20 | Difference |
|---|---|---|---|
| Overall Diameter | 670.6 mm (26.4") | 686.5 mm (27") | +15.9 mm |
| Section Width | 235 mm (9.3") | 255 mm (10") | +20 mm |
| Sidewall Height | 94 mm | 89.3 mm | -4.7 mm |
| Circumference | 2106.8 mm | 2156.7 mm | +49.9 mm |
| Revolutions/Mile | 764 | 746 | -18 |
| Aspect Ratio | 40% | 35% | -5% |
| Rim Diameter | 19" | 20" | +1" |
Key Impact Summary
Speedometer Correction Table
When switching from 235/40R19 to 255/35R20, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 mph |
| 40 mph | 40.9 mph | +0.9 mph |
| 50 mph | 51.2 mph | +1.2 mph |
| 60 mph | 61.4 mph | +1.4 mph |
| 70 mph | 71.7 mph | +1.7 mph |
| 80 mph | 81.9 mph | +1.9 mph |
| 90 mph | 92.1 mph | +2.1 mph |
| 100 mph | 102.4 mph | +2.4 mph |
| 110 mph | 112.6 mph | +2.6 mph |
| 120 mph | 122.8 mph | +2.8 mph |
What This Swap Means
Wider tires (255/35R20): The 20mm 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 4.7mm 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 7.9mm, providing slightly better approach angles for off-road driving and speed bump clearance.