305/65R17 vs 265/70R18

265/70R18 is 0.00 in (0.1 mm) shorter than 305/65R17, a −0.01% diameter difference. With the speedometer set for 305/65R17, an indicated 60 mph is 60.0 mph on 265/70R18.

Is this a safe swap?

Diameter difference −0.01%: under 1%

By overall diameter alone, 265/70R18 is a near match for 305/65R17; 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.

305/65R17 vs 265/70R18 differences
Measurement	305/65R17	265/70R18	Difference	% diff
Overall diameter	32.61 in (828.3 mm)	32.61 in (828.2 mm)	0.00 in (−0.1 mm)	−0.01%
Sidewall height	7.81 in (198.3 mm)	7.30 in (185.5 mm)	−0.50 in (−12.7 mm)	−6.43%
Section width	12.01 in (305.0 mm)	10.43 in (265.0 mm)	−1.57 in (−40.0 mm)	−13.11%
Circumference	102.45 in (2,602.2 mm)	102.44 in (2,601.9 mm)	−0.01 in (−0.3 mm)	−0.01%
Revolutions per mile	618	619	0	+0.01%

True speed with the speedometer calibrated for 305/65R17
Indicated	Actual on 305/65R17	Actual on 265/70R18
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 265/70R18 does not change the vehicle at the axle (half the −0.1 mm diameter difference).

265/70R18 is the same height as 305/65R17 and 40 mm narrower, a 0.01% difference in overall diameter.

With the speedometer calibrated for 305/65R17, an indicated 60 mph is actually 60.0 mph on 265/70R18, and revolutions per mile change from 618 to 619.

265/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 305/65R17.

Size pages

Other comparisons with 305/65R17

Other comparisons with 265/70R18

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