305/40R22 Tire Size in Inches

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

305/40R22
31.6" tall × 12.0" wide
On a 22-inch wheel · roughly 31.6x12.0R22 in flotation sizing
MeasurementInchesMillimetres
Overall diameter31.61803
Section width12.01305
Sidewall height4.80122.0
Wheel diameter22559
Circumference99.32522
Revolutions per mile638 (396 per km)

What 305/40R22 means

305 is the section width in millimetres (12.0 in). 40 is the aspect ratio: the sidewall is 40% as tall as the tire is wide, which works out to 122.0 mm or 4.8 in. R22 is a radial tire for a 22-inch wheel.

Overall diameter is the wheel plus two sidewalls: 22 + 2 × 4.80 = 31.6 inches. These are the nominal dimensions every maker builds to; a real 305/40R22 can measure a few tenths of an inch differently by model and inflation.

Closest equivalent sizes

Common sizes within the usual 3% of 305/40R22's overall diameter. Confirm load index, speed rating and rim width before swapping.

SizeDiameterWidthChangeSpeedometer at 60
265/70R17 new wheels 31.6 in 10.4 in +0.0% really 60.0 mph
265/65R18 new wheels 31.6 in 10.4 in -0.1% really 59.9 mph
265/75R16 new wheels 31.6 in 10.4 in +0.1% really 60.1 mph
235/85R16 new wheels 31.7 in 9.3 in +0.4% really 60.2 mph
245/75R17 new wheels 31.5 in 9.6 in -0.4% really 59.7 mph
285/60R18 new wheels 31.5 in 11.2 in -0.4% really 59.7 mph

Speedometer if you switch to 265/70R17

Your speedometer stays calibrated for 305/40R22. With a taller tire you travel faster than it shows.

Speedometer readsTrue speed
30 mph30.0 mph
45 mph45.0 mph
55 mph55.0 mph
65 mph65.0 mph
75 mph75.0 mph
Compare 305/40R22 with any size →

Shop 305/40R22 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 305/40R22 tire is 31.6 inches (803 mm) tall overall. That is the 22-inch wheel plus two sidewalls of 4.8 inches each (40% of the 305 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 305 mm, or 12.0 inches, measured sidewall to sidewall on the recommended rim width. The tread itself is narrower than that. In flotation sizing, 305/40R22 is roughly a 31.6x12.0R22.

265/70R17 is the closest common size, at +0.0% overall diameter (31.6 in against 31.6 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 638 revolutions per mile (396 per kilometre), from its 31.6-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 22-inch sizes

265/40R22 275/40R22 285/40R22 285/45R22 255/30R22 265/35R22 285/35R22 295/30R22 305/45R22