TireSizesFinder

295/40R20 vs 255/40R21

255/40R21 is 0.26 in (6.6 mm) shorter than 295/40R20, a −0.89% diameter difference. With the speedometer set for 295/40R20, an indicated 60 mph is 59.5 mph on 255/40R21.

Is this a safe swap?

Diameter difference −0.89%: under 1%

By overall diameter alone, 255/40R21 is a near match for 295/40R20; 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: 295/40R20 (29.29 in) vs 255/40R21 (29.03 in)295/40R2029.29 in × 11.61 in255/40R2129.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
295/40R20 vs 255/40R21 differences
Measurement295/40R20255/40R21Difference% diff
Overall diameter29.29 in (744.0 mm)29.03 in (737.4 mm)−0.26 in (−6.6 mm)−0.89%
Sidewall height4.65 in (118.0 mm)4.02 in (102.0 mm)−0.63 in (−16.0 mm)−13.56%
Section width11.61 in (295.0 mm)10.04 in (255.0 mm)−1.57 in (−40.0 mm)−13.56%
Circumference92.02 in (2,337.3 mm)91.21 in (2,316.6 mm)−0.82 in (−20.7 mm)−0.89%
Revolutions per mile689695+6+0.90%
True speed with the speedometer calibrated for 295/40R20
IndicatedActual on 295/40R20Actual on 255/40R21Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.5 mph−0.5 mph
75 mph75.0 mph74.3 mph−0.7 mph

Ride-height change: 255/40R21 lowers the vehicle by 0.13 in (3.3 mm) at the axle (half the −6.6 mm diameter difference).

255/40R21 is 0.26 in shorter than 295/40R20 and 40 mm narrower, a 0.89% difference in overall diameter.

With the speedometer calibrated for 295/40R20, an indicated 60 mph is actually 59.5 mph on 255/40R21, and revolutions per mile change from 689 to 695.

255/40R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 295/40R20.

Size pages

Other comparisons with 295/40R20

Other comparisons with 255/40R21

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