The 255/55R18 is a common tire size for SUVs and crossovers such as Toyota RAV4, Honda CR-V, and Ford Explorer.
With a 140.3 mm sidewall (55% aspect ratio), this tire offers a balanced blend of ride comfort and handling precision — versatile for both city driving and spirited cornering.
Compared to the baseline 235/45R18, this tire's overall diameter differs by +10.3% — a speedometer calibrated for 235/45R18 would read 90.6 km/h at an actual 100 km/h.
OE on the BMW X5 (E70) base, Mercedes-Benz ML350 (W164 2006-2010) and Audi Q7 (4L base). Load index 105V or 109W reinforced. Tall sidewall for a 255 mm width — favored on full-size SUVs where ride comfort matters more than steering crispness.
Crossover and mid-size SUV sizes carry significantly higher loads than passenger-car sizes of similar width, so the load index — not just the speed rating — is the spec to verify on replacement. Reinforced (XL/RF) versions are commonly OE; downgrading to standard-load risks sidewall failure on cargo-laden highway runs. Tread-pattern selection (H-T vs A-T) drives most of the noise and wet-grip difference.
| Tire Code | 255/55R18 |
| Section Width | 255 mm |
| Aspect Ratio | 55% |
| Rim Diameter | 18" |
| Sidewall Height | 140.3 mm |
| Overall Diameter | 737.7 mm / 29.04" |
| Circumference | 2317.6 mm / 91.24" |
| Revolutions per km | 431.5 |
| Revolutions per mile | 694.4 |
| Tire Code | OD (mm) | Δ mm | Δ % | Speedo at 100 km/h |
|---|---|---|---|---|
| 255/40R18 | 661.2 | -76.5 | -10.4% | 111.6 |
| 255/45R18 | 686.7 | -51.0 | -6.9% | 107.4 |
| 235/55R18 | 715.7 | -22.0 | -3.0% | 103.1 |
| 255/55R18 (current) | 737.7 | — | — | 100.0 |