245/45R20 vs 255/50R20 at a glance
| Measure | 245/45R20 (current) | 255/50R20 (new) | Difference |
|---|---|---|---|
| Overall height | 28.68 in | 30.04 in | +1.36 in (+4.74%) |
| Width | 9.65 in (245 mm) | 10.04 in (255 mm) | +10 mm |
| Sidewall | 4.34 in | 5.02 in | +0.68 in |
| Wheel | 20 in | 20 in | +0 in |
| Circumference | 90.1 in | 94.4 in | +4.3 in |
| Revs per mile | 703.2 | 671.4 | −31.8 |
Verdict: check clearance and speedometer
Over 3% and up to 5%: worth checking clearance, the speedometer and gearing before you buy. Going from 245/45R20 to 255/50R20 is a 4.7% increase in overall height (+1.36 in), and the vehicle sits about 0.68 in higher. The tire is 10 mm wider. The 3% rule of thumb comes from Discount Tire and 1010tires; it is not a guarantee of fit.
True speed and odometer
| Speedometer shows | You are really doing | Difference |
|---|---|---|
| 35 mph | 36.7 mph | +1.7 mph |
| 45 mph | 47.1 mph | +2.1 mph |
| 55 mph | 57.6 mph | +2.6 mph |
| 60 mph | 62.8 mph | +2.8 mph |
| 65 mph | 68.1 mph | +3.1 mph |
| 70 mph | 73.3 mph | +3.3 mph |
| 75 mph | 78.6 mph | +3.6 mph |
Odometer: 1,000 indicated miles is 1,047 real miles, and 10,000 is 10,474.
The math
245/45R20: 20 + 2 × (245 × 45% ÷ 25.4) = 28.68 in. 255/50R20: 20 + 2 × (255 × 50% ÷ 25.4) = 30.04 in. Change = 30.04 ÷ 28.68 − 1 = +4.74%. True speed at 60 = 60 × 30.04 ÷ 28.68 = 62.84 mph.
Check next
- Regear and RPM at cruise for this swap
- Speedometer and odometer correction
- Other sizes within ±3% of 245/45R20
Calculated from the size alone. Real tires vary a little by brand and model, and the loaded radius is a bit smaller. Confirm the wheel width range, clearance, load index and speed rating for your vehicle. See how to read a tire size, the load index chart and the speed rating chart.
Size pages: 245/45R20 · 255/50R20. More swaps: all tire size comparisons.