275/40R21 vs 265/45R21
265/45R21 is taller than 275/40R21 by 2.46% — a diameter difference of 0.73″.
What changes between 275/40R21 and 265/45R21
Switching from 275/40R21 to 265/45R21 changes overall diameter by +2.46%, a taller tire by 0.73 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″ (275mm → 265mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.36″: 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 66.6 mph. Both sizes share the same 21″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 275/40R21 | 265/45R21 |
|---|---|---|
| Overall diameter | 29.66″ | 30.39″ |
| Section width | 10.83″ (275 mm) | 10.43″ (265 mm) |
| Sidewall height | 4.33″ (40%) | 4.69″ (45%) |
| Rim diameter | 21″ | 21″ |
| Circumference | 93.18″ | 95.47″ |
| Revs per mile | 680 | 664 |
Interactive comparison
275/65R18 or "33" for inch aliases275/40R21
- Diameter
- 29.66″ / 753.4mm
- Section Width
- 10.83″
- Sidewall
- 4.33″ / 110mm
- Circumference
- 93.18″
- Revs/Mile
- 680
265/45R21
- Diameter
- 30.39″ / 771.9mm
- Section Width
- 10.43″
- Sidewall
- 4.69″ / 119.25mm
- Circumference
- 95.47″
- Revs/Mile
- 664
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 61.47 mph (98.93 km/h). Your speedometer reads 2.46% low versus actual speed.