TireSizesFinder

255/55R20 vs 265/50R21

265/50R21 is 0.39 in (9.9 mm) taller than 255/55R20, a +1.26% diameter difference. With the speedometer set for 255/55R20, an indicated 60 mph is 60.8 mph on 265/50R21.

Is this a safe swap?

Diameter difference +1.26%: within the ±3% guideline

By overall diameter alone, 265/50R21 falls inside the ±3% range commonly used as a guideline when replacing 255/55R20. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/55R20 (31.04 in) vs 265/50R21 (31.43 in)255/55R2031.04 in × 10.04 in265/50R2131.43 in × 10.43 in
Side profile and tread width, drawn to the same scale.
255/55R20 vs 265/50R21 differences
Measurement255/55R20265/50R21Difference% diff
Overall diameter31.04 in (788.5 mm)31.43 in (798.4 mm)+0.39 in (+9.9 mm)+1.26%
Sidewall height5.52 in (140.3 mm)5.22 in (132.5 mm)−0.31 in (−7.7 mm)−5.53%
Section width10.04 in (255.0 mm)10.43 in (265.0 mm)+0.39 in (+10.0 mm)+3.92%
Circumference97.53 in (2,477.1 mm)98.75 in (2,508.2 mm)+1.22 in (+31.1 mm)+1.26%
Revolutions per mile650642−8−1.24%
True speed with the speedometer calibrated for 255/55R20
IndicatedActual on 255/55R20Actual on 265/50R21Difference
30 mph30.0 mph30.4 mph+0.4 mph
60 mph60.0 mph60.8 mph+0.8 mph
75 mph75.0 mph75.9 mph+0.9 mph

Ride-height change: 265/50R21 raises the vehicle by 0.19 in (4.9 mm) at the axle (half the +9.9 mm diameter difference).

265/50R21 is 0.39 in taller than 255/55R20 and 10 mm wider, a 1.26% difference in overall diameter.

With the speedometer calibrated for 255/55R20, an indicated 60 mph is actually 60.8 mph on 265/50R21, and revolutions per mile change from 650 to 642.

265/50R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 255/55R20.

Size pages

Other comparisons with 255/55R20

Other comparisons with 265/50R21

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