245/40R18 vs 215/50R18
215/50R18 is taller than 245/40R18 by 2.91% — a diameter difference of 0.74″.
What changes between 245/40R18 and 215/50R18
Switching from 245/40R18 to 215/50R18 changes overall diameter by +2.91%, a taller tire by 0.74 inches. This lands inside the ±3% fitment safe zone, so most vehicles will accept the swap without rubbing, speedometer recalibration, or ABS/TPMS complications. Section width moves by -1.19″ (245mm → 215mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.37″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -22, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 66.9 mph. Both sizes share the same 18″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 245/40R18 | 215/50R18 |
|---|---|---|
| Overall diameter | 25.72″ | 26.46″ |
| Section width | 9.65″ (245 mm) | 8.46″ (215 mm) |
| Sidewall height | 3.86″ (40%) | 4.23″ (50%) |
| Rim diameter | 18″ | 18″ |
| Circumference | 80.79″ | 83.14″ |
| Revs per mile | 784 | 762 |
Interactive comparison
275/65R18 or "33" for inch aliases245/40R18
- Diameter
- 25.72″ / 653.2mm
- Section Width
- 9.65″
- Sidewall
- 3.86″ / 98mm
- Circumference
- 80.79″
- Revs/Mile
- 784
215/50R18
- Diameter
- 26.46″ / 672.2mm
- Section Width
- 8.46″
- Sidewall
- 4.23″ / 107.5mm
- Circumference
- 83.14″
- Revs/Mile
- 762
Speedometer & Diameter Impact
Narrower tire — verify wheel widthAt an indicated 60 mph, your actual speed is 61.75 mph (99.37 km/h). Your speedometer reads 2.91% low versus actual speed.