235/55R18 vs 305/45R18
305/45R18 is taller than 235/55R18 by 2.24% — a diameter difference of 0.63″.
What changes between 235/55R18 and 305/45R18
Switching from 235/55R18 to 305/45R18 changes overall diameter by +2.24%, 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 +2.76″ (235mm → 305mm), 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 -16, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 66.5 mph. Both sizes share the same 18″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 235/55R18 | 305/45R18 |
|---|---|---|
| Overall diameter | 28.18″ | 28.81″ |
| Section width | 9.25″ (235 mm) | 12.01″ (305 mm) |
| Sidewall height | 5.09″ (55%) | 5.4″ (45%) |
| Rim diameter | 18″ | 18″ |
| Circumference | 88.52″ | 90.5″ |
| Revs per mile | 716 | 700 |
Interactive comparison
275/65R18 or "33" for inch aliases235/55R18
- Diameter
- 28.18″ / 715.7mm
- Section Width
- 9.25″
- Sidewall
- 5.09″ / 129.25mm
- Circumference
- 88.52″
- Revs/Mile
- 716
305/45R18
- Diameter
- 28.81″ / 731.7mm
- Section Width
- 12.01″
- Sidewall
- 5.4″ / 137.25mm
- Circumference
- 90.5″
- Revs/Mile
- 700
Speedometer & Diameter Impact
Wider tire — verify wheel widthAt an indicated 60 mph, your actual speed is 61.34 mph (98.72 km/h). Your speedometer reads 2.24% low versus actual speed.