TireSizesFinder

295/35R20 vs 255/35R21

255/35R21 is 0.10 in (2.6 mm) shorter than 295/35R20, a −0.36% diameter difference. With the speedometer set for 295/35R20, an indicated 60 mph is 59.8 mph on 255/35R21.

Is this a safe swap?

Diameter difference −0.36%: under 1%

By overall diameter alone, 255/35R21 is a near match for 295/35R20; 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: 295/35R20 (28.13 in) vs 255/35R21 (28.03 in)295/35R2028.13 in × 11.61 in255/35R2128.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
295/35R20 vs 255/35R21 differences
Measurement295/35R20255/35R21Difference% diff
Overall diameter28.13 in (714.5 mm)28.03 in (711.9 mm)−0.10 in (−2.6 mm)−0.36%
Sidewall height4.06 in (103.3 mm)3.51 in (89.3 mm)−0.55 in (−14.0 mm)−13.56%
Section width11.61 in (295.0 mm)10.04 in (255.0 mm)−1.57 in (−40.0 mm)−13.56%
Circumference88.37 in (2,244.7 mm)88.05 in (2,236.5 mm)−0.32 in (−8.2 mm)−0.36%
Revolutions per mile717720+3+0.37%
True speed with the speedometer calibrated for 295/35R20
IndicatedActual on 295/35R20Actual on 255/35R21Difference
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: 255/35R21 lowers the vehicle by 0.05 in (1.3 mm) at the axle (half the −2.6 mm diameter difference).

255/35R21 is 0.10 in shorter than 295/35R20 and 40 mm narrower, a 0.36% difference in overall diameter.

With the speedometer calibrated for 295/35R20, an indicated 60 mph is actually 59.8 mph on 255/35R21, and revolutions per mile change from 717 to 720.

255/35R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 295/35R20.

Size pages

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