235/50R18 vs 225/55R18
225/55R18 is taller than 235/50R18 by 1.81% — a diameter difference of 0.49″.
What changes between 235/50R18 and 225/55R18
Switching from 235/50R18 to 225/55R18 changes overall diameter by +1.81%, a taller tire by 0.49 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 -0.39″ (235mm → 225mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.24″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -13, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 66.2 mph. Both sizes share the same 18″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 235/50R18 | 225/55R18 |
|---|---|---|
| Overall diameter | 27.25″ | 27.74″ |
| Section width | 9.25″ (235 mm) | 8.86″ (225 mm) |
| Sidewall height | 4.63″ (50%) | 4.87″ (55%) |
| Rim diameter | 18″ | 18″ |
| Circumference | 85.61″ | 87.16″ |
| Revs per mile | 740 | 727 |
Interactive comparison
275/65R18 or "33" for inch aliases235/50R18
- Diameter
- 27.25″ / 692.2mm
- Section Width
- 9.25″
- Sidewall
- 4.63″ / 117.5mm
- Circumference
- 85.61″
- Revs/Mile
- 740
225/55R18
- Diameter
- 27.74″ / 704.7mm
- Section Width
- 8.86″
- Sidewall
- 4.87″ / 123.75mm
- Circumference
- 87.16″
- Revs/Mile
- 727
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 61.08 mph (98.3 km/h). Your speedometer reads 1.81% low versus actual speed.