265/40R21 vs 315/35R21
315/35R21 is taller than 265/40R21 by 1.14% — a diameter difference of 0.33″.
What changes between 265/40R21 and 315/35R21
Switching from 265/40R21 to 315/35R21 changes overall diameter by +1.14%, a taller tire by 0.33 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 +1.97″ (265mm → 315mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.17″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -8, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 65.7 mph. Both sizes share the same 21″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 265/40R21 | 315/35R21 |
|---|---|---|
| Overall diameter | 29.35″ | 29.68″ |
| Section width | 10.43″ (265 mm) | 12.4″ (315 mm) |
| Sidewall height | 4.17″ (40%) | 4.34″ (35%) |
| Rim diameter | 21″ | 21″ |
| Circumference | 92.19″ | 93.25″ |
| Revs per mile | 687 | 679 |
Interactive comparison
275/65R18 or "33" for inch aliases265/40R21
- Diameter
- 29.35″ / 745.4mm
- Section Width
- 10.43″
- Sidewall
- 4.17″ / 106mm
- Circumference
- 92.19″
- Revs/Mile
- 687
315/35R21
- Diameter
- 29.68″ / 753.9mm
- Section Width
- 12.4″
- Sidewall
- 4.34″ / 110.25mm
- Circumference
- 93.25″
- Revs/Mile
- 679
Speedometer & Diameter Impact
Wider tire — verify wheel widthAt an indicated 60 mph, your actual speed is 60.68 mph (97.66 km/h). Your speedometer reads 1.14% low versus actual speed.