215/40R18 vs 215/45R18
215/45R18 is taller than 215/40R18 by 3.42% — a diameter difference of 0.85″.
What changes between 215/40R18 and 215/45R18
Switching from 215/40R18 to 215/45R18 changes overall diameter by +3.42%, a taller tire by 0.85 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 0.00″ (215mm → 215mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.42″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -27, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 67.2 mph. Both sizes share the same 18″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 215/40R18 | 215/45R18 |
|---|---|---|
| Overall diameter | 24.77″ | 25.62″ |
| Section width | 8.46″ (215 mm) | 8.46″ (215 mm) |
| Sidewall height | 3.39″ (40%) | 3.81″ (45%) |
| Rim diameter | 18″ | 18″ |
| Circumference | 77.82″ | 80.48″ |
| Revs per mile | 814 | 787 |
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
215/45R18
- Diameter
- 25.62″ / 650.7mm
- Section Width
- 8.46″
- Sidewall
- 3.81″ / 96.75mm
- Circumference
- 80.48″
- Revs/Mile
- 787
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 62.05 mph (99.86 km/h). Your speedometer reads 3.42% low versus actual speed.