What Size Are 31 Inch Tires? | Real Metric Matches

A 31-inch tire usually means about 31 inches tall overall, often in sizes like 31×10.50R15 or close metric equivalents.

A lot of drivers read “31-inch tires” and think the wheel must be 31 inches wide or 31 inches across. That is not how tire sizing works. In most cases, a 31-inch tire refers to the tire’s overall mounted diameter, not the wheel size sitting in the middle.

That is why the most familiar version is written as 31×10.50R15 or 31×10.50R15LT. The first number is the tire’s rough outside height. The second is the section width in inches. The last number is the wheel diameter. So a “31” usually rides on a 15-inch wheel, though some metric sizes on 16-inch or 17-inch wheels land close to the same height.

What Size Are 31 Inch Tires? The Common Metric Matches

If you want the plain answer, the classic 31-inch tire size is 31×10.50R15. That is the old-school flotation size many truck, SUV, and Jeep owners know by heart. On metric tires, there is no single one-size-fits-all match. You are looking for a size that lands near 31 inches tall once you combine width, sidewall height, and rim diameter.

That is where people get crossed up. A metric size like 255/70R17 can sit near 31.1 inches tall. A 265/65R17 lands closer to 30.6 inches. A 245/75R16 sits near 30.5 inches. All of them live in the same neighborhood, yet none is the exact same thing as a flotation-size 31×10.50R15.

Goodyear’s tire size terms spell out that high-flotation sizing uses outside diameter, section width, construction type, and rim diameter. That wording matters because it explains why the “31” points to tire height, not wheel size.

How The Numbers Break Down

• 31 = rough overall tire diameter in inches
• 10.50 = section width in inches
• R = radial construction
• 15 = wheel diameter in inches
• LT, when present, = light-truck service rating

One more thing: the listed diameter is nominal. Real measured height can shift a bit by brand, tread depth, wheel width, load range, and inflation pressure. A tire sold as a 31 may measure a touch under or a touch over once it is mounted.

31 Inch Tire Size Chart By Rim Diameter

The easiest way to compare a 31-inch tire with metric sizes is to treat 31 inches as the target outside diameter, then see which common metric sizes land close. This is why two trucks can both run “31s” and still show different sidewall numbers.

If you are swapping wheels, the rim diameter matters just as much as the tire height. A 15-inch wheel leaves more sidewall. A 17-inch wheel leaves less. The truck can still end up at nearly the same total height if the sidewall changes with it.

Width also changes the look and fit. A narrow near-31 can tuck inside the fender with less fuss. A wider one may sit fuller, grip differently, and brush the liner sooner. That is why two sizes that stand close in height can still call for different wheel widths and different clearance checks.

Use the chart below as a sorting tool, not a final fitment promise. It shows the sizes shoppers most often cross-shop when they want that classic 31-inch stance without guessing their way through every sidewall code.

Tire Size	Approx. Diameter	Where It Fits In The 31-Inch Range
31×10.50R15	31.0 in	The classic flotation-size 31 on a 15-inch wheel
265/75R15	30.6 in	Common metric size that runs a bit shorter
30×9.50R15	30.0 in	Close in style, but clearly smaller overall
245/75R16	30.5 in	Near-31 option with a narrower footprint
265/70R16	30.6 in	Popular truck size that sits just under 31
255/70R17	31.1 in	One of the closest 17-inch metric matches
265/65R17	30.6 in	Near the mark, with less sidewall than a 15
265/70R17	31.6 in	Falls into the same family, though it runs taller

That chart gives you the shape of the market. It is not a license to buy the nearest number and call it done. A half-inch swing in tire height can change rubbing, speedometer reading, and wheel-well space more than many drivers expect.

BFGoodrich’s 31/10.5R15 size page shows the same format in the wild, listing the size as 31 / 10.5 / R15. That gives you a clean real-world reference for what a true flotation-size 31 looks like on store listings.

How To Convert A 31-Inch Tire To Metric Without Guessing

Metric sizing looks messy until you know the formula. You take the section width in millimeters, multiply it by the aspect ratio, double that sidewall height, then convert to inches and add the rim diameter.

1. Multiply width by aspect ratio to get one sidewall height in millimeters.
2. Double it because the tire has a top sidewall and a bottom sidewall.
3. Divide by 25.4 to turn millimeters into inches.
4. Add the wheel diameter.

Say you are checking 255/70R17. The sidewall is 255 × 0.70 = 178.5 mm. Double that and you get 357 mm. Divide by 25.4 and you get about 14.06 inches. Add the 17-inch wheel and the full diameter lands near 31.06 inches.

That tells you why a 255/70R17 is such a common “31-ish” size. It is not sold as a 31, yet the math puts it right there.

Where 31-Inch Tire Swaps Change More Than The Number

Buying by diameter alone can bite you. Two tires that stand near 31 inches tall can feel different on the truck once width, tread shape, casing, and load range enter the picture.

• Clearance: Width can cause rub before height does, especially at full lock.
• Wheel fit: A tire may clear in diameter yet not suit your wheel width.
• Speedometer: Taller tires cover more ground per turn, so readings can drift.
• Gearing feel: A taller, heavier tire can soften low-speed punch.
• Ride: More sidewall usually cushions bumps better than a shorter sidewall on a bigger wheel.

Area	What Often Changes	What To Check
Fitment	Rubbing at the fender, liner, or sway bar	Full-lock clearance and suspension travel
Ride Feel	Softer or firmer impact feel	Sidewall height and load rating
Handling	Steering can feel slower with taller, heavier tires	Tire weight and tread pattern
Readings	Speedometer and odometer can read low	True mounted diameter
Fuel Use	Heavier tires can trim mileage	Weight, tread, and inflation

How To Pick The Right 31 For Your Truck Or SUV

Start with the wheel you already own. If it is a 15-inch wheel, a true 31×10.50R15 may be the cleanest answer. If you are on 17s, a near-31 metric size such as 255/70R17 may land closer to what you need with no wheel change.

Next, check the tire placard on the driver’s door and compare load rating, width, and inflation target. Then look at how you use the vehicle. Mud tires, all-terrain tires, and highway tires can all wear the same size on paper while behaving nothing alike on pavement.

Also check the measured specs on the exact tire you plan to buy. Brand-to-brand spread is real. One 31 can run short and narrow. Another can stand taller and carry a squarer shoulder. That is why the printed size gets you close, while the spec sheet settles the final call.

Getting The Answer Right

When someone asks, “What Size Are 31 Inch Tires?” the usual answer is 31×10.50R15. That is the classic flotation size. If you are shopping metric tires, think in terms of near-31 matches instead of one magic equivalent. The right pick depends on your wheel diameter, the width you want, and how much clearance your vehicle has to spare.

If you treat 31 inches as overall tire height, the whole topic gets easier. You stop mixing up wheel size with tire height, and you can compare flotation and metric sizes without the usual guesswork.