245/75R17 vs 255/75R17

255/75R17 is 0.59 in (15.0 mm) taller than 245/75R17, a +1.88% diameter difference. With the speedometer set for 245/75R17, an indicated 60 mph is 61.1 mph on 255/75R17.

Is this a safe swap?

Diameter difference +1.88%: within the ±3% guideline

By overall diameter alone, 255/75R17 falls inside the ±3% range commonly used as a guideline when replacing 245/75R17. 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.

245/75R17 vs 255/75R17 differences
Measurement	245/75R17	255/75R17	Difference	% diff
Overall diameter	31.47 in (799.3 mm)	32.06 in (814.3 mm)	+0.59 in (+15.0 mm)	+1.88%
Sidewall height	7.23 in (183.8 mm)	7.53 in (191.3 mm)	+0.30 in (+7.5 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	98.86 in (2,511.1 mm)	100.72 in (2,558.2 mm)	+1.86 in (+47.1 mm)	+1.88%
Revolutions per mile	641	629	−12	−1.84%

True speed with the speedometer calibrated for 245/75R17
Indicated	Actual on 245/75R17	Actual on 255/75R17	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.1 mph	+1.1 mph
75 mph	75.0 mph	76.4 mph	+1.4 mph

Ride-height change: 255/75R17 raises the vehicle by 0.30 in (7.5 mm) at the axle (half the +15.0 mm diameter difference).

255/75R17 is 0.59 in taller than 245/75R17 and 10 mm wider, a 1.88% difference in overall diameter.

With the speedometer calibrated for 245/75R17, an indicated 60 mph is actually 61.1 mph on 255/75R17, and revolutions per mile change from 641 to 629.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 245/75R17

Other comparisons with 255/75R17

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