TireSizesFinder

235/55R20 vs 295/40R21

295/40R21 is 0.11 in (2.9 mm) taller than 235/55R20, a +0.38% diameter difference. With the speedometer set for 235/55R20, an indicated 60 mph is 60.2 mph on 295/40R21.

Is this a safe swap?

Diameter difference +0.38%: under 1%

By overall diameter alone, 295/40R21 is a near match for 235/55R20; 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: 235/55R20 (30.18 in) vs 295/40R21 (30.29 in)235/55R2030.18 in × 9.25 in295/40R2130.29 in × 11.61 in
Side profile and tread width, drawn to the same scale.
235/55R20 vs 295/40R21 differences
Measurement235/55R20295/40R21Difference% diff
Overall diameter30.18 in (766.5 mm)30.29 in (769.4 mm)+0.11 in (+2.9 mm)+0.38%
Sidewall height5.09 in (129.3 mm)4.65 in (118.0 mm)−0.44 in (−11.2 mm)−8.70%
Section width9.25 in (235.0 mm)11.61 in (295.0 mm)+2.36 in (+60.0 mm)+25.53%
Circumference94.80 in (2,408.0 mm)95.16 in (2,417.1 mm)+0.36 in (+9.1 mm)+0.38%
Revolutions per mile668666−3−0.38%
True speed with the speedometer calibrated for 235/55R20
IndicatedActual on 235/55R20Actual on 295/40R21Difference
30 mph30.0 mph30.1 mph+0.1 mph
60 mph60.0 mph60.2 mph+0.2 mph
75 mph75.0 mph75.3 mph+0.3 mph

Ride-height change: 295/40R21 raises the vehicle by 0.06 in (1.4 mm) at the axle (half the +2.9 mm diameter difference).

295/40R21 is 0.11 in taller than 235/55R20 and 60 mm wider, a 0.38% difference in overall diameter.

With the speedometer calibrated for 235/55R20, an indicated 60 mph is actually 60.2 mph on 295/40R21, and revolutions per mile change from 668 to 666.

295/40R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 235/55R20.

Size pages

Other comparisons with 235/55R20

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