245/65R17 vs 275/55R18

275/55R18 is 0.37 in (9.4 mm) taller than 245/65R17, a +1.25% diameter difference. With the speedometer set for 245/65R17, an indicated 60 mph is 60.8 mph on 275/55R18.

Is this a safe swap?

Diameter difference +1.25%: within the ±3% guideline

By overall diameter alone, 275/55R18 falls inside the ±3% range commonly used as a guideline when replacing 245/65R17. 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.

245/65R17 vs 275/55R18 differences
Measurement	245/65R17	275/55R18	Difference	% diff
Overall diameter	29.54 in (750.3 mm)	29.91 in (759.7 mm)	+0.37 in (+9.4 mm)	+1.25%
Sidewall height	6.27 in (159.3 mm)	5.95 in (151.3 mm)	−0.31 in (−8.0 mm)	−5.02%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	92.80 in (2,357.1 mm)	93.96 in (2,386.7 mm)	+1.16 in (+29.5 mm)	+1.25%
Revolutions per mile	683	674	−8	−1.24%

True speed with the speedometer calibrated for 245/65R17
Indicated	Actual on 245/65R17	Actual on 275/55R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 275/55R18 raises the vehicle by 0.19 in (4.7 mm) at the axle (half the +9.4 mm diameter difference).

275/55R18 is 0.37 in taller than 245/65R17 and 30 mm wider, a 1.25% difference in overall diameter.

With the speedometer calibrated for 245/65R17, an indicated 60 mph is actually 60.8 mph on 275/55R18, and revolutions per mile change from 683 to 674.

275/55R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 245/65R17.

Size pages

Other comparisons with 245/65R17

Other comparisons with 275/55R18

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