245/45R17 vs 275/35R18

275/35R18 is 0.10 in (2.6 mm) shorter than 245/45R17, a −0.40% diameter difference. With the speedometer set for 245/45R17, an indicated 60 mph is 59.8 mph on 275/35R18.

Is this a safe swap?

Diameter difference −0.40%: under 1%

By overall diameter alone, 275/35R18 is a near match for 245/45R17; 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.

245/45R17 vs 275/35R18 differences
Measurement	245/45R17	275/35R18	Difference	% diff
Overall diameter	25.68 in (652.3 mm)	25.58 in (649.7 mm)	−0.10 in (−2.6 mm)	−0.40%
Sidewall height	4.34 in (110.3 mm)	3.79 in (96.3 mm)	−0.55 in (−14.0 mm)	−12.70%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	80.68 in (2,049.3 mm)	80.36 in (2,041.1 mm)	−0.32 in (−8.2 mm)	−0.40%
Revolutions per mile	785	788	+3	+0.40%

True speed with the speedometer calibrated for 245/45R17
Indicated	Actual on 245/45R17	Actual on 275/35R18	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.8 mph	−0.2 mph
75 mph	75.0 mph	74.7 mph	−0.3 mph

Ride-height change: 275/35R18 lowers the vehicle by 0.05 in (1.3 mm) at the axle (half the −2.6 mm diameter difference).

275/35R18 is 0.10 in shorter than 245/45R17 and 30 mm wider, a 0.40% difference in overall diameter.

With the speedometer calibrated for 245/45R17, an indicated 60 mph is actually 59.8 mph on 275/35R18, and revolutions per mile change from 785 to 788.

275/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 245/45R17.

Size pages

Other comparisons with 245/45R17

Other comparisons with 275/35R18

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