Semi truck tire size: how to read it and the common sizes

Diameters are approximate, calculated from the size for metric sizes and typical published figures for the numeric sizes. Actual diameter varies slightly by tire model and tread depth; check the tire maker's data book for exact figures.

How to read a metric truck tire size

Take 295/75R22.5 as an example:

• 295 is the section width in millimeters, about 11.6 inches.
• 75 is the aspect ratio: the sidewall height is 75 percent of the width.
• R means radial construction, used on nearly all modern truck tires.
• 22.5 is the wheel diameter in inches.

To estimate the overall diameter: sidewall height = 295 x 0.75 = about 221 mm, or 8.7 inches. Two sidewalls plus the wheel: 8.7 + 8.7 + 22.5 = about 39.9 inches.

How to read a numeric size

Older-style sizes such as 11R22.5 give the nominal width in inches (11), radial construction (R) and the wheel diameter (22.5). The sidewall height is not stated, but these tires are taller than most metric low-profile sizes, which is why an 11R22.5 is a little larger in diameter than a 295/75R22.5.

Common semi truck tire sizes

• 295/75R22.5 and 11R22.5: the most common sizes on tractors and trailers.
• 11R24.5 and 285/75R24.5: common where 24.5 inch wheels are used, often on older equipment and some vocational trucks.
• 445/50R22.5 and 455/55R22.5: wide-base single tires that replace a dual pair.
• 255/70R22.5 and other low-profile sizes: used on some trailers and car haulers where lower deck height helps.

Box trucks and medium duty trucks often use smaller sizes, such as 19.5 inch wheels with matching tires. Check your truck's placard.

Load range and ply rating

After the size, the sidewall shows the load range or ply rating, such as load range G or H. It tells you how much weight the tire can carry at a given pressure. Two tires of the same size can carry very different loads, so match the load range to your truck's needs and the vehicle maker's specification.

The sidewall also shows the maximum load for single and dual use and the maximum pressure. For setting pressure by load, see our guide to semi truck tire pressure.

Other sidewall markings

• DOT code: ends in four digits showing the week and year the tire was made.
• Load index and speed symbol on some tires, such as 146/143L, giving single and dual load capacity and a speed rating.
• Tread type and position markings on some lines.
• Regroovable on tires designed to be regrooved.

Why tire size matters

• Fit: the tire must match the wheel diameter and width.
• Load: the size and load range together decide what the tire can carry.
• Gearing: a taller tire turns fewer times per mile, which changes effective gearing and engine speed at cruise.
• Speedometer: changing tire diameter changes speedometer and odometer readings unless the truck is reprogrammed.
• Clearance: taller or wider tires may rub on fenders, mud flaps or suspension parts.
• Matching: duals must match closely in size and tread depth.

Choosing tires by size

Once you know your size, you can compare tire lines for each position. Our guide to semi truck tires explains steer, drive and trailer tires and the federal rules, and the guide to the best drive tires for a semi truck covers what to look for on drive axles. For prices by size and type, see how much semi truck tires cost.

Tire size and cost per mile

Larger or wide-base tires cost more each, but cost per mile depends on how long they last and whether they can be retreaded. The tire cost per mile calculator works out your cost per mile from price, tire count and miles.

Replacing with the right size

When a tire needs replacing on the road, give the service the exact size, load range and position. A replacement of a different size on a dual pair causes uneven loading and wear. If you are unsure whether a size change is allowed, check the vehicle maker's specifications or ask a tire professional. For damaged tires, see our guide to semi truck repair.

Truck tire sizes in inches

Some owners find it easier to think in inches. For common sizes, approximately:

• 295/75R22.5: about 11.6 inches wide and 39.9 inches tall.
• 11R22.5: about 11 inches nominal width and about 41 inches tall.
• 11R24.5: about 11 inches nominal width and about 43 inches tall.
• 285/75R24.5: about 11.2 inches wide and about 41 inches tall.
• 445/50R22.5: about 17.5 inches wide and about 40 inches tall.

These are approximate. Tread depth, the specific tire line and inflation pressure change the real figures slightly.

22.5 vs 24.5 inch wheels

The two main wheel diameters for heavy trucks are 22.5 and 24.5 inches. 22.5 inch wheels are the most common on modern tractors and trailers; the matching tires are widely stocked and often cost less. 24.5 inch wheels are found on some older equipment and some vocational trucks, and the tires are slightly taller. A truck must use tires that match its wheels, and changing wheel size is a bigger decision than changing tire brand.

Low-profile tires

Low-profile tires, with shorter sidewalls, lower the height of the vehicle. Car haulers use them to fit more vehicles within height limits, and some trailers use them for a lower deck or more cargo space. They usually carry less load per tire than taller tires of similar width, so check load ratings carefully.

Wide-base single tires

Wide-base singles replace a dual pair with one tire on a wider wheel. They save weight and can improve fuel economy, which is why many long haul fleets use them on drive and trailer axles. Drawbacks include no partner tire if one goes flat, possibly harder roadside replacement, and the need for matching wheels. If you switch, change all positions on an axle, and confirm the change is allowed for your vehicle.

Box truck tire sizes

Many box trucks and medium duty trucks use smaller sizes on 19.5 or 22.5 inch wheels, depending on the truck's weight rating. Check the tire placard, usually on the driver's door frame, for the original size and pressures. Matching the original size keeps the speedometer accurate and the load capacity correct.

Speedometer and odometer after a size change

Tire diameter decides how far the truck travels with each turn of the wheels. If you fit tires that are taller or shorter than the original size, the speedometer and odometer will read slightly wrong unless the engine's settings are updated. A small error matters: it affects speed, fuel economy calculations, maintenance intervals based on miles, and records kept for taxes such as IFTA. A shop can update the tire revolutions per mile setting in the engine's software.

Where to find your truck's correct size

The vehicle's tire and load information is usually on a placard or label on the driver's door frame, listing the original tire sizes, load ranges and cold inflation pressures. The truck's spec sheet and the tires currently fitted are other sources. If the current tires do not match the placard, find out why before buying replacements.

Where we fit

We are a dispatch desk for 26 ft box trucks and larger, not a tire seller. Learn more about our dispatch service.