The 225/40R18 is a common tire size for performance and sports cars such as BMW 3 Series, Volkswagen GTI, and Audi A4.
With a 90.0 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 -4.7% — a speedometer calibrated for 235/45R18 would read 104.9 km/h at an actual 100 km/h.
OE on the Mercedes-Benz CLA 250 (C117) and various German hot-hatch and performance-sedan 18" trims including VW Golf GTI Mk7 (Performance Pack) and Audi A3 (8V) S-Line. Load index 88Y or 92Y reinforced. Performance-sedan benchmark; UHP summer compound availability (Michelin PS4S, Conti SC7) is excellent.
Low-profile sizes in this group prioritize steering response and lateral grip over sidewall protection from pothole impacts. Curb-rash on the rim and pinched sidewalls are the dominant failure modes; insurance-claim data shows these sizes register two to three times more wheel damage than 50+ aspect ratios. Plan for a spare set of rims if the route includes broken urban pavement.
| Tire Code | 225/40R18 |
| Section Width | 225 mm |
| Aspect Ratio | 40% |
| Rim Diameter | 18" |
| Sidewall Height | 90.0 mm |
| Overall Diameter | 637.2 mm / 25.09" |
| Circumference | 2001.8 mm / 78.81" |
| Revolutions per km | 499.5 |
| Revolutions per mile | 803.9 |
| Tire Code | OD (mm) | Δ mm | Δ % | Speedo at 100 km/h |
|---|---|---|---|---|
| 215/40R18 | 629.2 | -8.0 | -1.3% | 101.3 |
| 225/40R18 (current) | 637.2 | — | — | 100.0 |
| 235/40R18 | 645.2 | +8.0 | +1.3% | 98.8 |
| 225/45R18 | 659.7 | +22.5 | +3.5% | 96.6 |
| 225/40R19 | 662.6 | +25.4 | +4.0% | 96.2 |