The 255/40R18 is a common tire size for performance and sports cars such as BMW 3 Series, Volkswagen GTI, and Audi A4.
With a 102.0 mm sidewall (40% aspect ratio), this low-profile tire delivers sharp steering response and precise cornering grip, though the ride feels firmer over rough surfaces.
Compared to the baseline 235/45R18, this tire's overall diameter differs by -1.1% — a speedometer calibrated for 235/45R18 would read 101.1 km/h at an actual 100 km/h.
When replacing, verify that your wheel well can accommodate the 661.2 mm overall diameter. Keep speedometer deviation within ±3% for safety and legal compliance.
| Tire Code | 255/40R18 |
| Section Width | 255 mm |
| Aspect Ratio | 40% |
| Rim Diameter | 18" |
| Sidewall Height | 102.0 mm |
| Overall Diameter | 661.2 mm / 26.03" |
| Circumference | 2077.2 mm / 81.78" |
| Revolutions per km | 481.4 |
| Revolutions per mile | 774.8 |
| Tire Code | OD (mm) | Δ mm | Δ % | Speedo at 100 km/h |
|---|---|---|---|---|
| 235/40R18 | 645.2 | -16.0 | -2.4% | 102.5 |
| 245/40R18 | 653.2 | -8.0 | -1.2% | 101.2 |
| 255/40R18 (current) | 661.2 | — | — | 100.0 |
| 255/40R19 | 686.6 | +25.4 | +3.8% | 96.3 |
| 255/45R18 | 686.7 | +25.5 | +3.9% | 96.3 |
| 255/55R18 | 737.7 | +76.5 | +11.6% | 89.6 |