TireSizesFinder

275/40R20 vs 275/35R21

275/35R21 is 0.08 in (2.1 mm) shorter than 275/40R20, a −0.29% diameter difference. With the speedometer set for 275/40R20, an indicated 60 mph is 59.8 mph on 275/35R21.

Is this a safe swap?

Diameter difference −0.29%: under 1%

By overall diameter alone, 275/35R21 is a near match for 275/40R20; 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: 275/40R20 (28.66 in) vs 275/35R21 (28.58 in)275/40R2028.66 in × 10.83 in275/35R2128.58 in × 10.83 in
Side profile and tread width, drawn to the same scale.
275/40R20 vs 275/35R21 differences
Measurement275/40R20275/35R21Difference% diff
Overall diameter28.66 in (728.0 mm)28.58 in (725.9 mm)−0.08 in (−2.1 mm)−0.29%
Sidewall height4.33 in (110.0 mm)3.79 in (96.3 mm)−0.54 in (−13.7 mm)−12.50%
Section width10.83 in (275.0 mm)10.83 in (275.0 mm)0.00 in (0.0 mm)0.00%
Circumference90.04 in (2,287.1 mm)89.78 in (2,280.5 mm)−0.26 in (−6.6 mm)−0.29%
Revolutions per mile704706+2+0.29%
True speed with the speedometer calibrated for 275/40R20
IndicatedActual on 275/40R20Actual on 275/35R21Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 275/35R21 lowers the vehicle by 0.04 in (1.1 mm) at the axle (half the −2.1 mm diameter difference).

275/35R21 is 0.08 in shorter than 275/40R20 and the same width, a 0.29% difference in overall diameter.

With the speedometer calibrated for 275/40R20, an indicated 60 mph is actually 59.8 mph on 275/35R21, and revolutions per mile change from 704 to 706.

275/35R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 275/40R20.

Size pages

Other comparisons with 275/40R20

Other comparisons with 275/35R21

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