255/70R15 vs 245/75R15

245/75R15 is 0.41 in (10.5 mm) taller than 255/70R15, a +1.42% diameter difference. With the speedometer set for 255/70R15, an indicated 60 mph is 60.9 mph on 245/75R15.

Is this a safe swap?

Diameter difference +1.42%: within the ±3% guideline

By overall diameter alone, 245/75R15 falls inside the ±3% range commonly used as a guideline when replacing 255/70R15. 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.

255/70R15 vs 245/75R15 differences
Measurement	255/70R15	245/75R15	Difference	% diff
Overall diameter	29.06 in (738.0 mm)	29.47 in (748.5 mm)	+0.41 in (+10.5 mm)	+1.42%
Sidewall height	7.03 in (178.5 mm)	7.23 in (183.8 mm)	+0.21 in (+5.3 mm)	+2.94%
Section width	10.04 in (255.0 mm)	9.65 in (245.0 mm)	−0.39 in (−10.0 mm)	−3.92%
Circumference	91.28 in (2,318.5 mm)	92.58 in (2,351.5 mm)	+1.30 in (+33.0 mm)	+1.42%
Revolutions per mile	694	684	−10	−1.40%

True speed with the speedometer calibrated for 255/70R15
Indicated	Actual on 255/70R15	Actual on 245/75R15	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 245/75R15 raises the vehicle by 0.21 in (5.3 mm) at the axle (half the +10.5 mm diameter difference).

245/75R15 is 0.41 in taller than 255/70R15 and 10 mm narrower, a 1.42% difference in overall diameter.

With the speedometer calibrated for 255/70R15, an indicated 60 mph is actually 60.9 mph on 245/75R15, and revolutions per mile change from 694 to 684.

Both sizes mount on 15-inch wheels.

Size pages

Other comparisons with 255/70R15

Other comparisons with 245/75R15

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