185/55R15 vs 205/50R15

205/50R15 is 0.06 in (1.5 mm) taller than 185/55R15, a +0.26% diameter difference. With the speedometer set for 185/55R15, an indicated 60 mph is 60.2 mph on 205/50R15.

Is this a safe swap?

Diameter difference +0.26%: under 1%

By overall diameter alone, 205/50R15 is a near match for 185/55R15; 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.

185/55R15 vs 205/50R15 differences
Measurement	185/55R15	205/50R15	Difference	% diff
Overall diameter	23.01 in (584.5 mm)	23.07 in (586.0 mm)	+0.06 in (+1.5 mm)	+0.26%
Sidewall height	4.01 in (101.8 mm)	4.04 in (102.5 mm)	+0.03 in (+0.8 mm)	+0.74%
Section width	7.28 in (185.0 mm)	8.07 in (205.0 mm)	+0.79 in (+20.0 mm)	+10.81%
Circumference	72.29 in (1,836.3 mm)	72.48 in (1,841.0 mm)	+0.19 in (+4.7 mm)	+0.26%
Revolutions per mile	876	874	−2	−0.26%

True speed with the speedometer calibrated for 185/55R15
Indicated	Actual on 185/55R15	Actual on 205/50R15	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 205/50R15 raises the vehicle by 0.03 in (0.8 mm) at the axle (half the +1.5 mm diameter difference).

205/50R15 is 0.06 in taller than 185/55R15 and 20 mm wider, a 0.26% difference in overall diameter.

With the speedometer calibrated for 185/55R15, an indicated 60 mph is actually 60.2 mph on 205/50R15, and revolutions per mile change from 876 to 874.

Both sizes mount on 15-inch wheels.

Size pages

Other comparisons with 185/55R15

Other comparisons with 205/50R15

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