255/40R17 Tire Size in Inches

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

255/40R17
25.0" tall × 10.0" wide
On a 17-inch wheel · roughly 25.0x10.0R17 in flotation sizing
MeasurementInchesMillimetres
Overall diameter25.03636
Section width10.04255
Sidewall height4.02102.0
Wheel diameter17432
Circumference78.61997
Revolutions per mile806 (501 per km)

What 255/40R17 means

255 is the section width in millimetres (10.0 in). 40 is the aspect ratio: the sidewall is 40% as tall as the tire is wide, which works out to 102.0 mm or 4.0 in. R17 is a radial tire for a 17-inch wheel.

Overall diameter is the wheel plus two sidewalls: 17 + 2 × 4.02 = 25.0 inches. These are the nominal dimensions every maker builds to; a real 255/40R17 can measure a few tenths of an inch differently by model and inflation.

Closest equivalent sizes

Common sizes within the usual 3% of 255/40R17's overall diameter. Confirm load index, speed rating and rim width before swapping.

SizeDiameterWidthChangeSpeedometer at 60
255/35R18 new wheels 25.0 in 10.0 in -0.0% really 60.0 mph
205/50R17 25.1 in 8.1 in +0.2% really 60.1 mph
195/65R15 new wheels 25.0 in 7.7 in -0.2% really 59.9 mph
225/40R18 new wheels 25.1 in 8.9 in +0.2% really 60.1 mph
225/45R17 25.0 in 8.9 in -0.2% really 59.9 mph
215/60R15 new wheels 25.2 in 8.5 in +0.5% really 60.3 mph

Speedometer if you switch to 205/50R17

Your speedometer stays calibrated for 255/40R17. With a taller tire you travel faster than it shows.

Speedometer readsTrue speed
30 mph30.0 mph
45 mph45.1 mph
55 mph55.1 mph
65 mph65.1 mph
75 mph75.1 mph
Compare 255/40R17 with any size →

Shop 255/40R17 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 255/40R17 tire is 25.0 inches (636 mm) tall overall. That is the 17-inch wheel plus two sidewalls of 4.0 inches each (40% of the 255 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 255 mm, or 10.0 inches, measured sidewall to sidewall on the recommended rim width. The tread itself is narrower than that. In flotation sizing, 255/40R17 is roughly a 25.0x10.0R17.

255/35R18 is the closest common size, at -0.0% overall diameter (25.0 in against 25.0 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 806 revolutions per mile (501 per kilometre), from its 25.0-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 17-inch sizes

205/40R17 205/50R17 205/55R17 215/45R17 215/50R17 215/55R17 215/60R17 215/65R17 225/45R17 225/50R17 225/55R17 225/60R17 225/65R17 235/45R17 235/55R17 235/60R17 235/65R17 235/70R17 235/80R17 245/40R17 245/45R17 245/65R17 245/70R17 245/75R17 255/60R17 255/65R17 255/70R17 255/75R17 265/65R17 265/70R17 275/65R17 275/70R17 285/70R17 285/75R17 315/70R17 235/50R17 275/60R17 305/65R17