245/40R20 vs 235/45R20
235/45R20 is taller than 245/40R20 by 2.20% — a diameter difference of 0.61″.
What changes between 245/40R20 and 235/45R20
Switching from 245/40R20 to 235/45R20 changes overall diameter by +2.20%, a taller tire by 0.61 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 -0.40″ (245mm → 235mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.30″: 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 66.4 mph. Both sizes share the same 20″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 245/40R20 | 235/45R20 |
|---|---|---|
| Overall diameter | 27.72″ | 28.33″ |
| Section width | 9.65″ (245 mm) | 9.25″ (235 mm) |
| Sidewall height | 3.86″ (40%) | 4.16″ (45%) |
| Rim diameter | 20″ | 20″ |
| Circumference | 87.07″ | 88.99″ |
| Revs per mile | 728 | 712 |
Interactive comparison
275/65R18 or "33" for inch aliases245/40R20
- Diameter
- 27.72″ / 704mm
- Section Width
- 9.65″
- Sidewall
- 3.86″ / 98mm
- Circumference
- 87.07″
- Revs/Mile
- 728
235/45R20
- Diameter
- 28.33″ / 719.5mm
- Section Width
- 9.25″
- Sidewall
- 4.16″ / 105.75mm
- Circumference
- 88.99″
- Revs/Mile
- 712
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 61.32 mph (98.69 km/h). Your speedometer reads 2.20% low versus actual speed.