Commercial Truck Tires: Steer, Drive and Trailer Explained

On a tractor-trailer, the steer, drive and trailer tires do different jobs, and tire makers design each one for its position. The right tire on each axle affects handling, traction, wear and how the truck fares at a roadside inspection. Below are the differences and what to check on the sidewall, using common 22.5- and 24.5-inch sizes such as 11R22.5, 295/75R22.5, 255/70R22.5 and 11R24.5 as examples.

Four positions, four different jobs

Steer. Front-axle tires handle steering, braking stability and straight tracking, and one major truck tire maker calls them the most important tires on the truck. They typically use a rib tread, with grooves running around the tire, which helps channel water and supports even wear.

Drive. Drive tires sit on the powered axles and put engine torque on the road. Makers use lug-type and siped tread designs here for traction, and drive patterns usually carry deeper tread. One maker gives typical ranges of about 11/32 to 23/32 inch for rib designs and 14/32 to 32/32 inch for lug designs.

Trailer. Trailer tires roll freely and do not steer or pull, but they carry loads that change from trip to trip and take strong side and braking forces. Tight turns with spread-axle or multi-axle trailers drag the tires sideways, and some trailer tires are designed for that high-scrub service. Many use reinforced sidewalls or protector ribs to resist curb damage.

All-position. These tires are designed to work on more than one axle, though one maker notes they are mostly built with the steer axle in mind. Data books list which positions each pattern is recommended for and which service it suits, such as long haul, regional, pickup and delivery, or on/off-highway work.

Rib vs. lug: why tread patterns differ

A rib tread has straight or zigzag grooves that run around the tire. It rolls with little resistance and supports directional stability and even wear, which is why tire makers say rib designs are usually found on steer axles and on free-rolling axles such as trailers.

A lug tread breaks the surface into blocks separated by grooves that run across the tire. Those crossways edges bite for traction under power, which is what a drive axle needs. Deeper, more open lug designs show up in on/off-highway and other vocational work, where grip matters more than low rolling resistance.

Standard and low-profile sizes

Sizes like 11R22.5 and 11R24.5 are standard-profile radials. Sizes like 295/75R22.5 and 285/75R24.5 are low-profile 75-series tires, and 255/70R22.5 is a 70-series size.

One major manufacturer lists possible advantages of 75-series low-profile tires over standard 90-series tires: more tread life, positive handling, lower vehicle height and lighter weight. It also says conversions take care, because overall diameter, loaded radius and maximum load all change. In its example, a 295/75R22.5 measures about 40.2 inches tall against 41.3 inches for an 11R22.5 in the same tread line. Check those numbers before you convert, and never mix sizes on the same axle.

Load range, ply rating and the dual load index

Commercial tires use the same load range letters as light truck tires, continued further up the alphabet. Load Range G equals a 14-ply rating and Load Range H a 16-ply rating. In the same size, the higher load range carries more weight, at a higher pressure.

Truck tires often show two load index numbers, such as 144/142. The first applies when the tire runs as a single, the second when it runs in a dual pair. One maker’s published tables for an 11R22.5 list:

• Load Range G (144/142): 6,175 lb single or 5,840 lb per tire in duals, at 105 psi.
• Load Range H (146/143): 6,610 lb single or 6,005 lb per tire in duals, at 120 psi.

A letter usually follows the load index. That is the speed symbol: L means 75 mph and M means 81 mph, the speed at which the tire can carry the load matching its load index under service conditions set by the maker.

Pressure follows the load. Federal rules bar running a tire above the load marked on its sidewall (except under a special state permit) or at a cold pressure below what is specified for the load it carries. Use the tire maker’s load and inflation tables for your actual axle weights. One major maker recommends checking pressure weekly with an accurate gauge while tires are cold, and warns that bleeding air from hot tires leaves them underinflated. It also cautions that a tire run at 80 percent or less of its normal pressure, or overloaded, could have permanent structural damage.

Matching duals and mixing tires

Tires in a dual assembly share the load, so they need to match. One major maker’s limits for radial duals are no more than 1/4 inch difference in diameter or 3/4 inch in circumference, and it says duals should also match in construction and design. It warns that poorly matched duals can cause irregular and rapid wear, mechanical problems and early tire failure.

• Do not mix tire sizes or constructions (radial and bias) on the same axle, and never mix constructions within a dual.
• Measure both tires of each dual pair, and check the inner tire’s pressure as carefully as the outer one.
• Keep records by wheel position so worn tires can be replaced in matched pairs.

Tread depth rules, regrooving and retreads

Under the FMCSA rule at 49 CFR 393.75, any tire on the front wheels of a bus, truck or truck tractor needs a tread groove depth of at least 4/32 inch, measured at any point on a major tread groove. All other tires need at least 2/32 inch. Measurements are not taken where tie bars, humps or fillets are located. The same rule bars running on a tire that is flat or has an audible leak, has tread or sidewall separation, or has ply or belt material exposed through the tread, the sidewall or a cut.

Regrooving is only for tires built for it. Federal rules require those tires to be labeled “Regroovable” on both sidewalls. A regrooved tire rated to carry 4,920 pounds or more may not be used on the front wheels of a truck or truck tractor, and buses may not run regrooved, recapped or retreaded tires on the front wheels at all.

Tire makers list retreadability as one of the factors in choosing truck tires, and their data books cover it. Whether retreads fit your operation is a call for your fleet and tire supplier.

Before you order

Confirm the size, load range, load index, speed symbol and wheel position against the tires now on the truck, your maintenance records and the vehicle’s certification label. That label lists the gross axle weight rating (GAWR) for each axle. On vehicles over 10,000 lb GVWR, the label or a separate tire label also shows the tire size and cold inflation pressure that go with each GAWR. A commercial tire professional or the maker’s data book can settle questions about load and inflation.

Browse truck and bus tires with your size, load range and wheel position in hand. If you are equipping a camper, boat or utility trailer rather than a semi-trailer, look at trailer tires instead. For pickups and vans that use LT sizes, see light truck tires.

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