165/70R14 vs 185/55R15

185/55R15 is 0.08 in (2.1 mm) shorter than 165/70R14, a −0.36% diameter difference. With the speedometer set for 165/70R14, an indicated 60 mph is 59.8 mph on 185/55R15.

Is this a safe swap?

Diameter difference −0.36%: under 1%

By overall diameter alone, 185/55R15 is a near match for 165/70R14; 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.

165/70R14 vs 185/55R15 differences
Measurement	165/70R14	185/55R15	Difference	% diff
Overall diameter	23.09 in (586.6 mm)	23.01 in (584.5 mm)	−0.08 in (−2.1 mm)	−0.36%
Sidewall height	4.55 in (115.5 mm)	4.01 in (101.8 mm)	−0.54 in (−13.7 mm)	−11.90%
Section width	6.50 in (165.0 mm)	7.28 in (185.0 mm)	+0.79 in (+20.0 mm)	+12.12%
Circumference	72.55 in (1,842.9 mm)	72.29 in (1,836.3 mm)	−0.26 in (−6.6 mm)	−0.36%
Revolutions per mile	873	876	+3	+0.36%

True speed with the speedometer calibrated for 165/70R14
Indicated	Actual on 165/70R14	Actual on 185/55R15	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: 185/55R15 lowers the vehicle by 0.04 in (1.0 mm) at the axle (half the −2.1 mm diameter difference).

185/55R15 is 0.08 in shorter than 165/70R14 and 20 mm wider, a 0.36% difference in overall diameter.

With the speedometer calibrated for 165/70R14, an indicated 60 mph is actually 59.8 mph on 185/55R15, and revolutions per mile change from 873 to 876.

185/55R15 mounts on a 15-inch wheel, a plus-1 fitment from the 14-inch wheel of 165/70R14.

Size pages

Other comparisons with 165/70R14

Other comparisons with 185/55R15

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