295/35R21 vs 315/35R21

315/35R21 is 0.55 in (14.0 mm) taller than 295/35R21, a +1.89% diameter difference. With the speedometer set for 295/35R21, an indicated 60 mph is 61.1 mph on 315/35R21.

Is this a safe swap?

Diameter difference +1.89%: within the ±3% guideline

By overall diameter alone, 315/35R21 falls inside the ±3% range commonly used as a guideline when replacing 295/35R21. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

295/35R21 vs 315/35R21 differences
Measurement	295/35R21	315/35R21	Difference	% diff
Overall diameter	29.13 in (739.9 mm)	29.68 in (753.9 mm)	+0.55 in (+14.0 mm)	+1.89%
Sidewall height	4.06 in (103.3 mm)	4.34 in (110.3 mm)	+0.28 in (+7.0 mm)	+6.78%
Section width	11.61 in (295.0 mm)	12.40 in (315.0 mm)	+0.79 in (+20.0 mm)	+6.78%
Circumference	91.51 in (2,324.5 mm)	93.25 in (2,368.4 mm)	+1.73 in (+44.0 mm)	+1.89%
Revolutions per mile	692	679	−13	−1.86%

True speed with the speedometer calibrated for 295/35R21
Indicated	Actual on 295/35R21	Actual on 315/35R21	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.1 mph	+1.1 mph
75 mph	75.0 mph	76.4 mph	+1.4 mph

Ride-height change: 315/35R21 raises the vehicle by 0.28 in (7.0 mm) at the axle (half the +14.0 mm diameter difference).

315/35R21 is 0.55 in taller than 295/35R21 and 20 mm wider, a 1.89% difference in overall diameter.

With the speedometer calibrated for 295/35R21, an indicated 60 mph is actually 61.1 mph on 315/35R21, and revolutions per mile change from 692 to 679.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 295/35R21

Other comparisons with 315/35R21

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.