265/65R18 vs 255/70R18

255/70R18 is 0.49 in (12.5 mm) taller than 265/65R18, a +1.56% diameter difference. With the speedometer set for 265/65R18, an indicated 60 mph is 60.9 mph on 255/70R18.

Is this a safe swap?

Diameter difference +1.56%: within the ±3% guideline

By overall diameter alone, 255/70R18 falls inside the ±3% range commonly used as a guideline when replacing 265/65R18. 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.

265/65R18 vs 255/70R18 differences
Measurement	265/65R18	255/70R18	Difference	% diff
Overall diameter	31.56 in (801.7 mm)	32.06 in (814.2 mm)	+0.49 in (+12.5 mm)	+1.56%
Sidewall height	6.78 in (172.3 mm)	7.03 in (178.5 mm)	+0.25 in (+6.3 mm)	+3.63%
Section width	10.43 in (265.0 mm)	10.04 in (255.0 mm)	−0.39 in (−10.0 mm)	−3.77%
Circumference	99.16 in (2,518.6 mm)	100.70 in (2,557.9 mm)	+1.55 in (+39.3 mm)	+1.56%
Revolutions per mile	639	629	−10	−1.54%

True speed with the speedometer calibrated for 265/65R18
Indicated	Actual on 265/65R18	Actual on 255/70R18	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.2 mph	+1.2 mph

Ride-height change: 255/70R18 raises the vehicle by 0.25 in (6.3 mm) at the axle (half the +12.5 mm diameter difference).

255/70R18 is 0.49 in taller than 265/65R18 and 10 mm narrower, a 1.56% difference in overall diameter.

With the speedometer calibrated for 265/65R18, an indicated 60 mph is actually 60.9 mph on 255/70R18, and revolutions per mile change from 639 to 629.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 265/65R18

Other comparisons with 255/70R18

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