TireSizesFinder

285/35R20 vs 245/35R21

245/35R21 is 0.10 in (2.6 mm) shorter than 285/35R20, a −0.37% diameter difference. With the speedometer set for 285/35R20, an indicated 60 mph is 59.8 mph on 245/35R21.

Is this a safe swap?

Diameter difference −0.37%: under 1%

By overall diameter alone, 245/35R21 is a near match for 285/35R20; 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: 285/35R20 (27.85 in) vs 245/35R21 (27.75 in)285/35R2027.85 in × 11.22 in245/35R2127.75 in × 9.65 in
Side profile and tread width, drawn to the same scale.
285/35R20 vs 245/35R21 differences
Measurement285/35R20245/35R21Difference% diff
Overall diameter27.85 in (707.5 mm)27.75 in (704.9 mm)−0.10 in (−2.6 mm)−0.37%
Sidewall height3.93 in (99.8 mm)3.38 in (85.8 mm)−0.55 in (−14.0 mm)−14.04%
Section width11.22 in (285.0 mm)9.65 in (245.0 mm)−1.57 in (−40.0 mm)−14.04%
Circumference87.51 in (2,222.7 mm)87.19 in (2,214.5 mm)−0.32 in (−8.2 mm)−0.37%
Revolutions per mile724727+3+0.37%
True speed with the speedometer calibrated for 285/35R20
IndicatedActual on 285/35R20Actual on 245/35R21Difference
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: 245/35R21 lowers the vehicle by 0.05 in (1.3 mm) at the axle (half the −2.6 mm diameter difference).

245/35R21 is 0.10 in shorter than 285/35R20 and 40 mm narrower, a 0.37% difference in overall diameter.

With the speedometer calibrated for 285/35R20, an indicated 60 mph is actually 59.8 mph on 245/35R21, and revolutions per mile change from 724 to 727.

245/35R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 285/35R20.

Size pages

Other comparisons with 285/35R20

Other comparisons with 245/35R21

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