185/70R13 vs 205/50R15

205/50R15 is 0.13 in (3.2 mm) shorter than 185/70R13, a −0.54% diameter difference. With the speedometer set for 185/70R13, an indicated 60 mph is 59.7 mph on 205/50R15.

Is this a safe swap?

Diameter difference −0.54%: under 1%

By overall diameter alone, 205/50R15 is a near match for 185/70R13; 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.

185/70R13 vs 205/50R15 differences
Measurement	185/70R13	205/50R15	Difference	% diff
Overall diameter	23.20 in (589.2 mm)	23.07 in (586.0 mm)	−0.13 in (−3.2 mm)	−0.54%
Sidewall height	5.10 in (129.5 mm)	4.04 in (102.5 mm)	−1.06 in (−27.0 mm)	−20.85%
Section width	7.28 in (185.0 mm)	8.07 in (205.0 mm)	+0.79 in (+20.0 mm)	+10.81%
Circumference	72.88 in (1,851.0 mm)	72.48 in (1,841.0 mm)	−0.40 in (−10.1 mm)	−0.54%
Revolutions per mile	869	874	+5	+0.55%

True speed with the speedometer calibrated for 185/70R13
Indicated	Actual on 185/70R13	Actual on 205/50R15	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: 205/50R15 lowers the vehicle by 0.06 in (1.6 mm) at the axle (half the −3.2 mm diameter difference).

205/50R15 is 0.13 in shorter than 185/70R13 and 20 mm wider, a 0.54% difference in overall diameter.

With the speedometer calibrated for 185/70R13, an indicated 60 mph is actually 59.7 mph on 205/50R15, and revolutions per mile change from 869 to 874.

205/50R15 mounts on a 15-inch wheel, a plus-2 fitment from the 13-inch wheel of 185/70R13.

Size pages

Other comparisons with 185/70R13

Other comparisons with 205/50R15

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