175/55R15 vs 185/55R15

185/55R15 is 0.43 in (11.0 mm) taller than 175/55R15, a +1.92% diameter difference. With the speedometer set for 175/55R15, an indicated 60 mph is 61.2 mph on 185/55R15.

Is this a safe swap?

Diameter difference +1.92%: within the ±3% guideline

By overall diameter alone, 185/55R15 falls inside the ±3% range commonly used as a guideline when replacing 175/55R15. 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.

175/55R15 vs 185/55R15 differences
Measurement	175/55R15	185/55R15	Difference	% diff
Overall diameter	22.58 in (573.5 mm)	23.01 in (584.5 mm)	+0.43 in (+11.0 mm)	+1.92%
Sidewall height	3.79 in (96.3 mm)	4.01 in (101.8 mm)	+0.22 in (+5.5 mm)	+5.71%
Section width	6.89 in (175.0 mm)	7.28 in (185.0 mm)	+0.39 in (+10.0 mm)	+5.71%
Circumference	70.93 in (1,801.7 mm)	72.29 in (1,836.3 mm)	+1.36 in (+34.6 mm)	+1.92%
Revolutions per mile	893	876	−17	−1.88%

True speed with the speedometer calibrated for 175/55R15
Indicated	Actual on 175/55R15	Actual on 185/55R15	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.2 mph	+1.2 mph
75 mph	75.0 mph	76.4 mph	+1.4 mph

Ride-height change: 185/55R15 raises the vehicle by 0.22 in (5.5 mm) at the axle (half the +11.0 mm diameter difference).

185/55R15 is 0.43 in taller than 175/55R15 and 10 mm wider, a 1.92% difference in overall diameter.

With the speedometer calibrated for 175/55R15, an indicated 60 mph is actually 61.2 mph on 185/55R15, and revolutions per mile change from 893 to 876.

Both sizes mount on 15-inch wheels.

Size pages

Other comparisons with 175/55R15

Other comparisons with 185/55R15

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