255/50R21 vs 275/50R21

275/50R21 is 0.79 in (20.0 mm) taller than 255/50R21, a +2.54% diameter difference. With the speedometer set for 255/50R21, an indicated 60 mph is 61.5 mph on 275/50R21.

Is this a safe swap?

Diameter difference +2.54%: within the ±3% guideline

By overall diameter alone, 275/50R21 falls inside the ±3% range commonly used as a guideline when replacing 255/50R21. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

255/50R21 vs 275/50R21 differences
Measurement	255/50R21	275/50R21	Difference	% diff
Overall diameter	31.04 in (788.4 mm)	31.83 in (808.4 mm)	+0.79 in (+20.0 mm)	+2.54%
Sidewall height	5.02 in (127.5 mm)	5.41 in (137.5 mm)	+0.39 in (+10.0 mm)	+7.84%
Section width	10.04 in (255.0 mm)	10.83 in (275.0 mm)	+0.79 in (+20.0 mm)	+7.84%
Circumference	97.51 in (2,476.8 mm)	99.99 in (2,539.7 mm)	+2.47 in (+62.8 mm)	+2.54%
Revolutions per mile	650	634	−16	−2.47%

True speed with the speedometer calibrated for 255/50R21
Indicated	Actual on 255/50R21	Actual on 275/50R21	Difference
30 mph	30.0 mph	30.8 mph	+0.8 mph
60 mph	60.0 mph	61.5 mph	+1.5 mph
75 mph	75.0 mph	76.9 mph	+1.9 mph

Ride-height change: 275/50R21 raises the vehicle by 0.39 in (10.0 mm) at the axle (half the +20.0 mm diameter difference).

275/50R21 is 0.79 in taller than 255/50R21 and 20 mm wider, a 2.54% difference in overall diameter.

With the speedometer calibrated for 255/50R21, an indicated 60 mph is actually 61.5 mph on 275/50R21, and revolutions per mile change from 650 to 634.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 255/50R21

Other comparisons with 275/50R21

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.