215/40R18 vs 245/40R18
245/40R18 is taller than 215/40R18 by 3.81% — a diameter difference of 0.95″.
What changes between 215/40R18 and 245/40R18
Switching from 215/40R18 to 245/40R18 changes overall diameter by +3.81%, a taller tire by 0.95 inches. This sits in the 3–5% caution band, where rubbing at full steering lock or suspension compression becomes possible. Leveling kits or fender-liner trims are often needed on lifted trucks. Section width moves by +1.19″ (215mm → 245mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.47″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -30, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 67.5 mph. Both sizes share the same 18″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 215/40R18 | 245/40R18 |
|---|---|---|
| Overall diameter | 24.77″ | 25.72″ |
| Section width | 8.46″ (215 mm) | 9.65″ (245 mm) |
| Sidewall height | 3.39″ (40%) | 3.86″ (40%) |
| Rim diameter | 18″ | 18″ |
| Circumference | 77.82″ | 80.79″ |
| Revs per mile | 814 | 784 |
Interactive comparison
275/65R18 or "33" for inch aliases215/40R18
- Diameter
- 24.77″ / 629.2mm
- Section Width
- 8.46″
- Sidewall
- 3.39″ / 86mm
- Circumference
- 77.82″
- Revs/Mile
- 814
245/40R18
- Diameter
- 25.72″ / 653.2mm
- Section Width
- 9.65″
- Sidewall
- 3.86″ / 98mm
- Circumference
- 80.79″
- Revs/Mile
- 784
Speedometer & Diameter Impact
Wider tire — verify wheel widthAt an indicated 60 mph, your actual speed is 62.29 mph (100.24 km/h). Your speedometer reads 3.81% low versus actual speed.