255/40R19 Tire Size in Inches

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

255/40R19
27.0" tall × 10.0" wide
On a 19-inch wheel · roughly 27.0x10.0R19 in flotation sizing
MeasurementInchesMillimetres
Overall diameter27.03687
Section width10.04255
Sidewall height4.02102.0
Wheel diameter19483
Circumference84.92157
Revolutions per mile746 (464 per km)

What 255/40R19 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. R19 is a radial tire for a 19-inch wheel.

Overall diameter is the wheel plus two sidewalls: 19 + 2 × 4.02 = 27.0 inches. These are the nominal dimensions every maker builds to; a real 255/40R19 can measure a few tenths of an inch differently by model and inflation.

Closest equivalent sizes

Common sizes within the usual 3% of 255/40R19's overall diameter. Confirm load index, speed rating and rim width before swapping.

SizeDiameterWidthChangeSpeedometer at 60
255/35R20 new wheels 27.0 in 10.0 in -0.0% really 60.0 mph
255/45R18 new wheels 27.0 in 10.0 in +0.0% really 60.0 mph
215/65R16 new wheels 27.0 in 8.5 in -0.1% really 59.9 mph
225/45R19 27.0 in 8.9 in -0.2% really 59.9 mph
235/60R16 new wheels 27.1 in 9.3 in +0.3% really 60.2 mph
205/75R15 new wheels 27.1 in 8.1 in +0.3% really 60.2 mph

Speedometer if you switch to 225/45R19

Your speedometer stays calibrated for 255/40R19. With a shorter tire you travel slower than it shows.

Speedometer readsTrue speed
30 mph29.9 mph
45 mph44.9 mph
55 mph54.9 mph
65 mph64.9 mph
75 mph74.8 mph
Compare 255/40R19 with any size →

Shop 255/40R19 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 255/40R19 tire is 27.0 inches (687 mm) tall overall. That is the 19-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, 255/40R19 is roughly a 27.0x10.0R19.

255/35R20 is the closest common size, at -0.0% overall diameter (27.0 in against 27.0 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 746 revolutions per mile (464 per kilometre), from its 27.0-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 19-inch sizes

225/40R19 225/45R19 225/55R19 235/35R19 235/40R19 235/45R19 235/50R19 235/55R19 245/35R19 245/40R19 245/45R19 245/50R19 245/55R19 255/35R19 255/45R19 255/50R19 255/55R19 265/50R19 275/35R19 275/40R19 275/45R19 285/45R19 275/55R19 285/40R19