TireSizesFinder

245/55R20 vs 295/40R21

295/40R21 is 0.32 in (8.1 mm) shorter than 245/55R20, a −1.04% diameter difference. With the speedometer set for 245/55R20, an indicated 60 mph is 59.4 mph on 295/40R21.

Is this a safe swap?

Diameter difference −1.04%: within the ±3% guideline

By overall diameter alone, 295/40R21 falls inside the ±3% range commonly used as a guideline when replacing 245/55R20. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 245/55R20 (30.61 in) vs 295/40R21 (30.29 in)245/55R2030.61 in × 9.65 in295/40R2130.29 in × 11.61 in
Side profile and tread width, drawn to the same scale.
245/55R20 vs 295/40R21 differences
Measurement245/55R20295/40R21Difference% diff
Overall diameter30.61 in (777.5 mm)30.29 in (769.4 mm)−0.32 in (−8.1 mm)−1.04%
Sidewall height5.31 in (134.8 mm)4.65 in (118.0 mm)−0.66 in (−16.7 mm)−12.43%
Section width9.65 in (245.0 mm)11.61 in (295.0 mm)+1.97 in (+50.0 mm)+20.41%
Circumference96.16 in (2,442.6 mm)95.16 in (2,417.1 mm)−1.00 in (−25.4 mm)−1.04%
Revolutions per mile659666+7+1.05%
True speed with the speedometer calibrated for 245/55R20
IndicatedActual on 245/55R20Actual on 295/40R21Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.2 mph−0.8 mph

Ride-height change: 295/40R21 lowers the vehicle by 0.16 in (4.1 mm) at the axle (half the −8.1 mm diameter difference).

295/40R21 is 0.32 in shorter than 245/55R20 and 50 mm wider, a 1.04% difference in overall diameter.

With the speedometer calibrated for 245/55R20, an indicated 60 mph is actually 59.4 mph on 295/40R21, and revolutions per mile change from 659 to 666.

295/40R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 245/55R20.

Size pages

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