215/40R18 vs 235/40R18
235/40R18 is taller than 215/40R18 by 2.54% — a diameter difference of 0.63″.
What changes between 215/40R18 and 235/40R18
Switching from 215/40R18 to 235/40R18 changes overall diameter by +2.54%, a taller tire by 0.63 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 +0.79″ (215mm → 235mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.31″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -20, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 66.7 mph. Both sizes share the same 18″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 215/40R18 | 235/40R18 |
|---|---|---|
| Overall diameter | 24.77″ | 25.4″ |
| Section width | 8.46″ (215 mm) | 9.25″ (235 mm) |
| Sidewall height | 3.39″ (40%) | 3.7″ (40%) |
| Rim diameter | 18″ | 18″ |
| Circumference | 77.82″ | 79.8″ |
| Revs per mile | 814 | 794 |
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
235/40R18
- Diameter
- 25.4″ / 645.2mm
- Section Width
- 9.25″
- Sidewall
- 3.7″ / 94mm
- Circumference
- 79.8″
- Revs/Mile
- 794
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 61.53 mph (99.02 km/h). Your speedometer reads 2.54% low versus actual speed.