245/45R18 vs 255/45R18 at a glance
| Measure | 245/45R18 (current) | 255/45R18 (new) | Difference |
|---|---|---|---|
| Overall height | 26.68 in | 27.04 in | +0.35 in (+1.33%) |
| Width | 9.65 in (245 mm) | 10.04 in (255 mm) | +10 mm |
| Sidewall | 4.34 in | 4.52 in | +0.18 in |
| Wheel | 18 in | 18 in | +0 in |
| Circumference | 83.8 in | 84.9 in | +1.1 in |
| Revs per mile | 755.9 | 746.0 | −9.9 |
Verdict: close match
Within the 3% rule of thumb, so the speedometer, gearing and ride height change little. Going from 245/45R18 to 255/45R18 is a 1.3% increase in overall height (+0.35 in), and the vehicle sits about 0.18 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 | 35.5 mph | +0.5 mph |
| 45 mph | 45.6 mph | +0.6 mph |
| 55 mph | 55.7 mph | +0.7 mph |
| 60 mph | 60.8 mph | +0.8 mph |
| 65 mph | 65.9 mph | +0.9 mph |
| 70 mph | 70.9 mph | +0.9 mph |
| 75 mph | 76.0 mph | +1.0 mph |
Odometer: 1,000 indicated miles is 1,013 real miles, and 10,000 is 10,133.
The math
245/45R18: 18 + 2 × (245 × 45% ÷ 25.4) = 26.68 in. 255/45R18: 18 + 2 × (255 × 45% ÷ 25.4) = 27.04 in. Change = 27.04 ÷ 26.68 − 1 = +1.33%. True speed at 60 = 60 × 27.04 ÷ 26.68 = 60.80 mph.
Check next
- Regear and RPM at cruise for this swap
- Speedometer and odometer correction
- Other sizes within ±3% of 245/45R18
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: 245/45R18 · 255/45R18. More swaps: all tire size comparisons.