255/75R17 vs 265/65R18

265/65R18 is 0.50 in (12.6 mm) shorter than 255/75R17, a −1.55% diameter difference. With the speedometer set for 255/75R17, an indicated 60 mph is 59.1 mph on 265/65R18.

Is this a safe swap?

Diameter difference −1.55%: within the ±3% guideline

By overall diameter alone, 265/65R18 falls inside the ±3% range commonly used as a guideline when replacing 255/75R17. 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.

255/75R17 vs 265/65R18 differences
Measurement	255/75R17	265/65R18	Difference	% diff
Overall diameter	32.06 in (814.3 mm)	31.56 in (801.7 mm)	−0.50 in (−12.6 mm)	−1.55%
Sidewall height	7.53 in (191.3 mm)	6.78 in (172.3 mm)	−0.75 in (−19.0 mm)	−9.93%
Section width	10.04 in (255.0 mm)	10.43 in (265.0 mm)	+0.39 in (+10.0 mm)	+3.92%
Circumference	100.72 in (2,558.2 mm)	99.16 in (2,518.6 mm)	−1.56 in (−39.6 mm)	−1.55%
Revolutions per mile	629	639	+10	+1.57%

True speed with the speedometer calibrated for 255/75R17
Indicated	Actual on 255/75R17	Actual on 265/65R18	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.8 mph	−1.2 mph

Ride-height change: 265/65R18 lowers the vehicle by 0.25 in (6.3 mm) at the axle (half the −12.6 mm diameter difference).

265/65R18 is 0.50 in shorter than 255/75R17 and 10 mm wider, a 1.55% difference in overall diameter.

With the speedometer calibrated for 255/75R17, an indicated 60 mph is actually 59.1 mph on 265/65R18, and revolutions per mile change from 629 to 639.

265/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/75R17.

Size pages

Other comparisons with 255/75R17

Other comparisons with 265/65R18

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