TireSizesFinder

315/35R20 vs 275/35R21

275/35R21 is 0.10 in (2.6 mm) shorter than 315/35R20, a −0.36% diameter difference. With the speedometer set for 315/35R20, an indicated 60 mph is 59.8 mph on 275/35R21.

Is this a safe swap?

Diameter difference −0.36%: under 1%

By overall diameter alone, 275/35R21 is a near match for 315/35R20; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 315/35R20 (28.68 in) vs 275/35R21 (28.58 in)315/35R2028.68 in × 12.40 in275/35R2128.58 in × 10.83 in
Side profile and tread width, drawn to the same scale.
315/35R20 vs 275/35R21 differences
Measurement315/35R20275/35R21Difference% diff
Overall diameter28.68 in (728.5 mm)28.58 in (725.9 mm)−0.10 in (−2.6 mm)−0.36%
Sidewall height4.34 in (110.3 mm)3.79 in (96.3 mm)−0.55 in (−14.0 mm)−12.70%
Section width12.40 in (315.0 mm)10.83 in (275.0 mm)−1.57 in (−40.0 mm)−12.70%
Circumference90.10 in (2,288.7 mm)89.78 in (2,280.5 mm)−0.32 in (−8.2 mm)−0.36%
Revolutions per mile703706+3+0.36%
True speed with the speedometer calibrated for 315/35R20
IndicatedActual on 315/35R20Actual on 275/35R21Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.7 mph−0.3 mph

Ride-height change: 275/35R21 lowers the vehicle by 0.05 in (1.3 mm) at the axle (half the −2.6 mm diameter difference).

275/35R21 is 0.10 in shorter than 315/35R20 and 40 mm narrower, a 0.36% difference in overall diameter.

With the speedometer calibrated for 315/35R20, an indicated 60 mph is actually 59.8 mph on 275/35R21, and revolutions per mile change from 703 to 706.

275/35R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 315/35R20.

Size pages

Other comparisons with 315/35R20

Other comparisons with 275/35R21

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.