245/50R20 vs 255/50R20

255/50R20 is 0.39 in (10.0 mm) taller than 245/50R20, a +1.33% diameter difference. With the speedometer set for 245/50R20, an indicated 60 mph is 60.8 mph on 255/50R20.

Is this a safe swap?

Diameter difference +1.33%: within the ±3% guideline

By overall diameter alone, 255/50R20 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.

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

245/50R20 vs 255/50R20 differences
Measurement	245/50R20	255/50R20	Difference	% diff
Overall diameter	29.65 in (753.0 mm)	30.04 in (763.0 mm)	+0.39 in (+10.0 mm)	+1.33%
Sidewall height	4.82 in (122.5 mm)	5.02 in (127.5 mm)	+0.20 in (+5.0 mm)	+4.08%
Section width	9.65 in (245.0 mm)	10.04 in (255.0 mm)	+0.39 in (+10.0 mm)	+4.08%
Circumference	93.13 in (2,365.6 mm)	94.37 in (2,397.0 mm)	+1.24 in (+31.4 mm)	+1.33%
Revolutions per mile	680	671	−9	−1.31%

True speed with the speedometer calibrated for 245/50R20
Indicated	Actual on 245/50R20	Actual on 255/50R20	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 255/50R20 raises the vehicle by 0.20 in (5.0 mm) at the axle (half the +10.0 mm diameter difference).

255/50R20 is 0.39 in taller than 245/50R20 and 10 mm wider, a 1.33% difference in overall diameter.

With the speedometer calibrated for 245/50R20, an indicated 60 mph is actually 60.8 mph on 255/50R20, and revolutions per mile change from 680 to 671.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 245/50R20

Other comparisons with 255/50R20

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