185/55R15 Tire Size in Inches

Diameter, width, sidewall and the closest equivalent sizes, computed from the size code.

185/55R15
23.0" tall × 7.3" wide
On a 15-inch wheel · roughly 23.0x7.3R15 in flotation sizing
MeasurementInchesMillimetres
Overall diameter23.01585
Section width7.28185
Sidewall height4.01101.8
Wheel diameter15381
Circumference72.31836
Revolutions per mile876 (545 per km)

What 185/55R15 means

185 is the section width in millimetres (7.3 in). 55 is the aspect ratio: the sidewall is 55% as tall as the tire is wide, which works out to 101.8 mm or 4.0 in. R15 is a radial tire for a 15-inch wheel.

Overall diameter is the wheel plus two sidewalls: 15 + 2 × 4.01 = 23.0 inches. These are the nominal dimensions every maker builds to; a real 185/55R15 can measure a few tenths of an inch differently by model and inflation.

Closest equivalent sizes

Common sizes within the usual 3% of 185/55R15's overall diameter. Confirm load index, speed rating and rim width before swapping.

SizeDiameterWidthChangeSpeedometer at 60
175/65R14 new wheels 23.0 in 6.9 in -0.2% really 59.9 mph
195/60R14 new wheels 23.2 in 7.7 in +0.9% really 60.5 mph
205/45R16 new wheels 23.3 in 8.1 in +1.1% really 60.7 mph
185/60R14 new wheels 22.7 in 7.3 in -1.2% really 59.3 mph
195/55R15 23.4 in 7.7 in +1.9% really 61.1 mph
205/40R17 new wheels 23.5 in 8.1 in +1.9% really 61.2 mph

Speedometer if you switch to 195/55R15

Your speedometer stays calibrated for 185/55R15. With a taller tire you travel faster than it shows.

Speedometer readsTrue speed
30 mph30.6 mph
45 mph45.8 mph
55 mph56.0 mph
65 mph66.2 mph
75 mph76.4 mph
Compare 185/55R15 with any size →

Shop 185/55R15 tires

Check the load index and speed rating on your door-jamb placard before you buy, especially for LT tires used for towing.

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Frequently Asked Questions

A 185/55R15 tire is 23.0 inches (585 mm) tall overall. That is the 15-inch wheel plus two sidewalls of 4.0 inches each (55% of the 185 mm section width). Expect a real tire to measure within a few tenths of an inch of this, depending on the model and inflation.

The section width is 185 mm, or 7.3 inches, measured sidewall to sidewall on the recommended rim width. The tread itself is narrower than that. In flotation sizing, 185/55R15 is roughly a 23.0x7.3R15.

175/65R14 is the closest common size, at -0.2% overall diameter (23.0 in against 23.0 in). Most makers treat about 3% as the limit for a swap without speedometer or clearance problems, but always confirm load index, speed rating and wheel width before changing size.

About 876 revolutions per mile (545 per kilometre), from its 23.0-inch rolling diameter. Real-world figures run slightly higher because a loaded tire squats. This number is what your speedometer and odometer are calibrated against.

Last updated: October 2, 2026

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Other 15-inch sizes

175/65R15 185/60R15 185/65R15 195/55R15 195/60R15 195/65R15 205/60R15 205/65R15 205/70R15 205/75R15 215/60R15 215/65R15 215/70R15 215/75R15 225/60R15 225/70R15 225/75R15 235/70R15 235/75R15