How much do you have invested in your tires? For a tractor, it may total anywhere from $1,800 for four recaps and two new steers to $4,000 for all-new premium tires. A trailer can add $1,200 to $3,200. Tires are a rig’s second-largest maintenance/operating expense after fuel. How can you protect that investment?

Keep your tires properly inflated at all times. This is the most important thing, and we can’t stress it enough. Pressurized air is a structural part of the tire, as important as the steel belts, radial cords or rubber itself. Check inflation pressure – with a gauge – at least weekly.

Air keeps the tire from flexing too much. Flexing generates heat inside the tire, and excessive heat ruins tires. Without enough air, flexing can heat the tire past the temperature at which rubber becomes liquid. When that happens, the tire can’t hold together, and pieces start to fly off.

Look at the next “gator tail” you see. Chances are it has steel cords coming out. That’s not a thrown retread. It’s a section of a casing that let go due to excessive heat, usually caused directly by low air pressure. This has been proven by actual collection and analysis of rubber pieces.

Proper air pressure depends on load and speed. A tire filled to 85 psi may be safe when running empty, but it will need 100 psi to carry 80,000 pounds safely at 65 mph. The same tire may need 115 to 120 psi to handle 75 to 80 mph without excessive flexing. Every maker has load-speed tables for its tires. Tire casings become damaged when running about 20% under proper inflation pressure for any sustained period. For a tire rated at 100 psi at 55 mph, 20% under-inflation could be 96 psi at 75 mph.

Match sizes. Keep tires in a dual set matched as closely for size as possible. One-quarter inch radius difference is the recommended maximum, but if you can, keep tire diameters matched as close to 1/8 inch as possible. Since the two tires are bolted together at the wheels, they turn the same number revolutions per mile, even though their diameters differ. One-quarter inch difference in radius (one-half inch diameter) will cause the larger to carry 600 pounds more than the smaller one. It will also wear out faster; both will wear unevenly.

It is not uncommon to have this much difference when drivers buy one used tire to replace a damaged tire on a set of duals. Drive tires can have as much as a full inch of tread depth (32/32 inch), so one can wear 1-3/4 inches off its diameter and still be legal. Also, even if perfectly matched by size, inflation differences will affect wear and load. At a 15-psi difference, the higher-pressure tire will carry 500 pounds more than the other.

Balance tires whenever servicing them. Much of the pavement pounding by loaded as well as empty trailers occurs because an imbalance wants to pull the tire off the pavement, then slam it back down as the tire rotates. Imbalance causes uneven wear.

Align all wheels. The Technology and Maintenance Council (TMC) of ATA recommends total vehicle alignment. This means all wheels and axles are in proper alignment, not just the tractor’s steer tires. Axles must be perpendicular to the vehicle center line to avoid wear from thrust forces set up by wheels pointed slightly to the side. Check annually.

Check steer tires for toe-in or toe-out, caster and camber. Toe is where the tires are pointing when seen from above. Caster is the angle of the steering assembly kingpin with the ground, as seen from the side. Camber is the tires leaning inward or outward when seen from the front or rear. Each of these affects tire wear, and uneven wear cuts tire life.

Check for uneven wear at least weekly. Run your hand over the tread to feel for cupping, saw-toothing or rounded shoulders.

Establishing your own tire maintenance program is easy and will increase the use you get from your tires. If you maintain your tires well, you can have your own casings re-treaded so you know your retread’s history. A good casing, kept inflated, aligned and balanced, should last two or three re-treadings, giving 500,000 miles or more total wear. Even if you don’t want to run retreads, a good casing is worth around $60 in trade.

The government wants you to know when air pressure in your tires gets low, but it can’t just legislate the technology to do that.

The Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act of 2000 directs NHTSA to develop regulations requiring vehicles to be equipped with tire pressure warning systems. The implementation date is Nov. 1, 2003. Passed in the wake of the Firestone/Ford Explorer tire problems, the law was written with SUVs and autos in mind. As written, it applies to heavy trucks and tractor-trailers, too.

Tire pressure monitoring exists today. General Motors, for example, has it as standard or an option on 14 vehicles. Johnson Controls will soon have aftermarket units that transmit data to a special rear-view mirror containing a read-out. Dana Spicer makes a pressure monitoring system for commercial vehicles. But, designed more for pre- and post-trip inspections than for continuous use, it transmits to a reader that must be near the tire.

In theory, transmitters could send signals to tractor- and trailer-mounted receivers. The trailer unit would then have to send its signal to the in-cab alert unit, either by radio frequency or, more likely, through the multiplexed PLC4TRUCKS system now used to light the trailer ABS malfunction light in the cab. ArvinMeritor now sells the PSI trailer tire inflations system. It doesn’t yet include a monitor, but that’s coming – and of course, the system keeps tires inflated, anyway. Although that technology has not yet been developed, it will probably be available before the 2003 implementation date.