205/55R16 vs 245/35R18

245/35R18 is 0.13 in (3.2 mm) shorter than 205/55R16, a −0.51% diameter difference. With the speedometer set for 205/55R16, an indicated 60 mph is 59.7 mph on 245/35R18.

Is this a safe swap?

Diameter difference −0.51%: under 1%

By overall diameter alone, 245/35R18 is a near match for 205/55R16; 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.

205/55R16 vs 245/35R18 differences
Measurement	205/55R16	245/35R18	Difference	% diff
Overall diameter	24.88 in (631.9 mm)	24.75 in (628.7 mm)	−0.13 in (−3.2 mm)	−0.51%
Sidewall height	4.44 in (112.8 mm)	3.38 in (85.8 mm)	−1.06 in (−27.0 mm)	−23.95%
Section width	8.07 in (205.0 mm)	9.65 in (245.0 mm)	+1.57 in (+40.0 mm)	+19.51%
Circumference	78.16 in (1,985.2 mm)	77.76 in (1,975.1 mm)	−0.40 in (−10.1 mm)	−0.51%
Revolutions per mile	811	815	+4	+0.51%

True speed with the speedometer calibrated for 205/55R16
Indicated	Actual on 205/55R16	Actual on 245/35R18	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.7 mph	−0.3 mph
75 mph	75.0 mph	74.6 mph	−0.4 mph

Ride-height change: 245/35R18 lowers the vehicle by 0.06 in (1.6 mm) at the axle (half the −3.2 mm diameter difference).

245/35R18 is 0.13 in shorter than 205/55R16 and 40 mm wider, a 0.51% difference in overall diameter.

With the speedometer calibrated for 205/55R16, an indicated 60 mph is actually 59.7 mph on 245/35R18, and revolutions per mile change from 811 to 815.

245/35R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 205/55R16.

Size pages

Other comparisons with 205/55R16

Other comparisons with 245/35R18

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