40x12.50R17 tire size

40x12.50R17 in numbers

40x12.50R17 prints its own height: 40 inches (1016 mm) overall and 12.5 inches (318 mm) wide. On a 17 inch rim that leaves 11.5 inches (292 mm) of sidewall per side, which is an aspect ratio of about 92 even though none is printed. One turn covers 3192 mm (125.7 in), so it turns about 313 times per kilometre and 504 times per mile, or 522 times a minute at 100 km/h. Of the 95 flotation sizes listed here, 7 are taller and 79 are shorter. 9 other flotation sizes come within 3 percent of its diameter; the closest is 40x13.50R17, the same to within 0.01 percent.

What each part of 40x12.50R17 means

40

Overall diameter in inches, printed on the tire. This is the whole tire, not the tread width. Misreading it as a width is the commonest mistake with this format.

12.5

Section width in inches (317.5 mm).

R

Radial construction. The R here is construction, not the speed symbol R. The speed symbol sits after the size, in the service description.

17

Rim diameter in inches. The bead seat diameter of the wheel this tire mounts on.

no prefix

Euro-metric (no prefix). An unprefixed size is Euro-metric, not P-metric with the P left off. The prefix decides which standards body's load table rates the tire. What the prefixes mean

Dimensions 40x12.50R17 implies

These are the nominal dimensions the size code implies. A real tire's measured dimensions depend on its mould, its construction and the rim width it is mounted on, so a manufacturer's specification sheet for a specific tire is the authority for that tire.

Sizes within 3 percent of 40x12.50R17, any rim

The 9 sizes in this catalog closest to 40x12.50R17 in overall diameter, of the same type, ranked by how little they change it. The speedometer columns assume the instrument read correctly on 40x12.50R17 and that nothing was recalibrated.

A positive difference means the replacement is taller, so the vehicle travels further per revolution and the speedometer reads LOW. Many vehicles leave the factory reading slightly high on purpose, so treat this as a change from whatever the instrument did before, not as an absolute claim about it.

Plus one: 18 inch rim, same rolling diameter

A bigger wheel with a shorter sidewall, holding the overall diameter within 3 percent. Only sizes inside that window are listed - a "plus size" that changes the diameter by six percent is a different tire, not an alternative.

A positive difference means the replacement is taller, so the vehicle travels further per revolution and the speedometer reads LOW. Many vehicles leave the factory reading slightly high on purpose, so treat this as a change from whatever the instrument did before, not as an absolute claim about it.

Same 318 mm width, different aspect ratio

What changing only the aspect ratio does, holding the width and the rim.

• 29x12.50R1529 in
• 33x12.50R1533 in
• 33x12.50R1733 in
• 33x12.50R1833 in
• 33x12.50R2033 in
• 33x12.50R2233 in

Questions this size raises

What does 40x12.50R17 mean?

It is a flotation size, quoted in inches. 40 is the tire's overall diameter, 12.5 is its section width, R means radial construction and 17 is the rim diameter it mounts on. The first number is the whole tire, not the tread width, which is the most common misreading of this format.

How tall is a 40x12.50R17 tire?

40 inches (1016 mm) in nominal overall diameter. That is the diameter the size code implies; a specific tire's measured diameter depends on its mould and the rim width it is mounted on, and the manufacturer's specification sheet is the authority for that tire.

What is the sidewall height of a 40x12.50R17?

11.5 inches (292.1 mm) per side.

How many revolutions per mile does a 40x12.50R17 turn?

504 revolutions per mile, from the nominal circumference of 125.7 inches. A loaded tire deflects and turns slightly more often than that, so a manufacturer's published revolutions figure usually runs a few percent higher.

What is the plus one size for 40x12.50R17?

40x13.50R18 keeps the overall diameter closest on a rim one inch larger, of the sizes in this catalog. Plus sizing trades sidewall for wheel while holding the rolling diameter, so the speedometer stays close to correct. Whether the wheel and tire clear the vehicle is a separate question this site cannot answer.

The rest of the sidewall

The size is one line of a sidewall. What follows it decides whether the tire is legal on the vehicle at all.

• Load index table - the number after the size, and the mass it stands for. Must meet or exceed the vehicle placard.
• Speed symbol table - the letter after the load index, including the ZR, W, Y and (Y) cases.
• DOT date code - how old the tire is, and why a three digit code is not the same as a four digit one.
• Every other marking - UTQG grades, load range letters, M+S against the three peak mountain snowflake.
• Compare 40x12.50R17 against another size - diameter, clearance and speedometer error side by side.