235/75R15 vs 255/70R15

255/70R15 is 0.18 in (4.5 mm) taller than 235/75R15, a +0.61% diameter difference. With the speedometer set for 235/75R15, an indicated 60 mph is 60.4 mph on 255/70R15.

Is this a safe swap?

Diameter difference +0.61%: under 1%

By overall diameter alone, 255/70R15 is a near match for 235/75R15; the speedometer changes by less than 1%. 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.

235/75R15 vs 255/70R15 differences
Measurement	235/75R15	255/70R15	Difference	% diff
Overall diameter	28.88 in (733.5 mm)	29.06 in (738.0 mm)	+0.18 in (+4.5 mm)	+0.61%
Sidewall height	6.94 in (176.3 mm)	7.03 in (178.5 mm)	+0.09 in (+2.3 mm)	+1.28%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	90.72 in (2,304.4 mm)	91.28 in (2,318.5 mm)	+0.56 in (+14.1 mm)	+0.61%
Revolutions per mile	698	694	−4	−0.61%

True speed with the speedometer calibrated for 235/75R15
Indicated	Actual on 235/75R15	Actual on 255/70R15	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 255/70R15 raises the vehicle by 0.09 in (2.3 mm) at the axle (half the +4.5 mm diameter difference).

255/70R15 is 0.18 in taller than 235/75R15 and 20 mm wider, a 0.61% difference in overall diameter.

With the speedometer calibrated for 235/75R15, an indicated 60 mph is actually 60.4 mph on 255/70R15, and revolutions per mile change from 698 to 694.

Both sizes mount on 15-inch wheels.

Size pages

Other comparisons with 235/75R15

Other comparisons with 255/70R15

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