165/65R14 vs 185/55R15

185/55R15 is 0.57 in (14.4 mm) taller than 165/65R14, a +2.53% diameter difference. With the speedometer set for 165/65R14, an indicated 60 mph is 61.5 mph on 185/55R15.

Is this a safe swap?

Diameter difference +2.53%: within the ±3% guideline

By overall diameter alone, 185/55R15 falls inside the ±3% range commonly used as a guideline when replacing 165/65R14. 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.

165/65R14 vs 185/55R15 differences
Measurement	165/65R14	185/55R15	Difference	% diff
Overall diameter	22.44 in (570.1 mm)	23.01 in (584.5 mm)	+0.57 in (+14.4 mm)	+2.53%
Sidewall height	4.22 in (107.3 mm)	4.01 in (101.8 mm)	−0.22 in (−5.5 mm)	−5.13%
Section width	6.50 in (165.0 mm)	7.28 in (185.0 mm)	+0.79 in (+20.0 mm)	+12.12%
Circumference	70.51 in (1,791.0 mm)	72.29 in (1,836.3 mm)	+1.78 in (+45.2 mm)	+2.53%
Revolutions per mile	899	876	−22	−2.46%

True speed with the speedometer calibrated for 165/65R14
Indicated	Actual on 165/65R14	Actual on 185/55R15	Difference
30 mph	30.0 mph	30.8 mph	+0.8 mph
60 mph	60.0 mph	61.5 mph	+1.5 mph
75 mph	75.0 mph	76.9 mph	+1.9 mph

Ride-height change: 185/55R15 raises the vehicle by 0.28 in (7.2 mm) at the axle (half the +14.4 mm diameter difference).

185/55R15 is 0.57 in taller than 165/65R14 and 20 mm wider, a 2.53% difference in overall diameter.

With the speedometer calibrated for 165/65R14, an indicated 60 mph is actually 61.5 mph on 185/55R15, and revolutions per mile change from 899 to 876.

185/55R15 mounts on a 15-inch wheel, a plus-1 fitment from the 14-inch wheel of 165/65R14.

Size pages

Other comparisons with 165/65R14

Other comparisons with 185/55R15

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