TireSizesFinder

245/50R20 vs 265/40R21

265/40R21 is 0.30 in (7.6 mm) shorter than 245/50R20, a −1.01% diameter difference. With the speedometer set for 245/50R20, an indicated 60 mph is 59.4 mph on 265/40R21.

Is this a safe swap?

Diameter difference −1.01%: within the ±3% guideline

By overall diameter alone, 265/40R21 falls inside the ±3% range commonly used as a guideline when replacing 245/50R20. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 245/50R20 (29.65 in) vs 265/40R21 (29.35 in)245/50R2029.65 in × 9.65 in265/40R2129.35 in × 10.43 in
Side profile and tread width, drawn to the same scale.
245/50R20 vs 265/40R21 differences
Measurement245/50R20265/40R21Difference% diff
Overall diameter29.65 in (753.0 mm)29.35 in (745.4 mm)−0.30 in (−7.6 mm)−1.01%
Sidewall height4.82 in (122.5 mm)4.17 in (106.0 mm)−0.65 in (−16.5 mm)−13.47%
Section width9.65 in (245.0 mm)10.43 in (265.0 mm)+0.79 in (+20.0 mm)+8.16%
Circumference93.13 in (2,365.6 mm)92.19 in (2,341.7 mm)−0.94 in (−23.9 mm)−1.01%
Revolutions per mile680687+7+1.02%
True speed with the speedometer calibrated for 245/50R20
IndicatedActual on 245/50R20Actual on 265/40R21Difference
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: 265/40R21 lowers the vehicle by 0.15 in (3.8 mm) at the axle (half the −7.6 mm diameter difference).

265/40R21 is 0.30 in shorter than 245/50R20 and 20 mm wider, a 1.01% difference in overall diameter.

With the speedometer calibrated for 245/50R20, an indicated 60 mph is actually 59.4 mph on 265/40R21, and revolutions per mile change from 680 to 687.

265/40R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 245/50R20.

Size pages

Other comparisons with 245/50R20

Other comparisons with 265/40R21

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