275/40R20 Tire Size in Inches

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

275/40R20
28.7" tall × 10.8" wide
On a 20-inch wheel · roughly 28.7x10.8R20 in flotation sizing
MeasurementInchesMillimetres
Overall diameter28.66728
Section width10.83275
Sidewall height4.33110.0
Wheel diameter20508
Circumference90.02287
Revolutions per mile704 (437 per km)

What 275/40R20 means

275 is the section width in millimetres (10.8 in). 40 is the aspect ratio: the sidewall is 40% as tall as the tire is wide, which works out to 110.0 mm or 4.3 in. R20 is a radial tire for a 20-inch wheel.

Overall diameter is the wheel plus two sidewalls: 20 + 2 × 4.33 = 28.7 inches. These are the nominal dimensions every maker builds to; a real 275/40R20 can measure a few tenths of an inch differently by model and inflation.

Closest equivalent sizes

Common sizes within the usual 3% of 275/40R20's overall diameter. Confirm load index, speed rating and rim width before swapping.

SizeDiameterWidthChangeSpeedometer at 60
245/50R19 new wheels 28.6 in 9.6 in -0.1% really 60.0 mph
245/45R20 28.7 in 9.6 in +0.1% really 60.0 mph
315/35R20 28.7 in 12.4 in +0.1% really 60.0 mph
225/60R18 new wheels 28.6 in 8.9 in -0.1% really 59.9 mph
225/55R19 new wheels 28.7 in 8.9 in +0.3% really 60.2 mph
275/45R19 new wheels 28.7 in 10.8 in +0.3% really 60.2 mph

Speedometer if you switch to 245/45R20

Your speedometer stays calibrated for 275/40R20. 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 mph75.1 mph
Compare 275/40R20 with any size →

Shop 275/40R20 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 275/40R20 tire is 28.7 inches (728 mm) tall overall. That is the 20-inch wheel plus two sidewalls of 4.3 inches each (40% of the 275 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 275 mm, or 10.8 inches, measured sidewall to sidewall on the recommended rim width. The tread itself is narrower than that. In flotation sizing, 275/40R20 is roughly a 28.7x10.8R20.

245/50R19 is the closest common size, at -0.1% overall diameter (28.6 in against 28.7 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 704 revolutions per mile (437 per kilometre), from its 28.7-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 20-inch sizes

235/35R20 235/45R20 235/55R20 245/35R20 245/40R20 245/45R20 245/50R20 255/35R20 255/40R20 255/45R20 255/50R20 255/55R20 265/40R20 265/45R20 265/50R20 275/35R20 275/45R20 275/50R20 275/55R20 275/60R20 275/65R20 285/45R20 285/50R20 285/55R20 285/60R20 285/65R20 295/35R20 295/45R20 305/55R20 295/55R20 295/60R20 305/50R20 315/35R20