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Getting the most miles from your tires

Let's see now; 18 tires at $300 each. That's $5,400 tied up in tire cost. Recaps are less, of course, and a good, retreadable carcass is worth, oh, maybe $100 to $125. With re-treaded drive and trailer wheels, the investment is still well over $3,000. Even if you pull someone else's trailer, you've still got $2,000 to $3,000 invested in rubber.

Never mind that those 18 little patches of rubber, each about one square foot or less, have to support your rig and transmit all your acceleration, braking and cornering forces. Just think of the money. Or perhaps more importantly, think of the safety factors. Either way, there is ample motivation to maintain your tires. Yet tires are among the most ignored components on a truck, especially during pre-trip inspections.

Most drivers thump tires. But thumping does not let you know if your tires are up to pressure. In test after test, drivers have never been able to identify low tires as long as pressure was at least 65 psi. That's 35 percent below specification for a 100 psi tire, 28 percent low for 90 psi. Tire manufacturers tell us that any tire run for a sustained period at just 20 percent under specified pressure will be permanently weakened and unsuitable for recapping. Before trying to air it up, it should be removed from its wheel and inspected by a technician. Chances are that internal cord damage occurred. A failure called a "zipper" is common when tires that have run under-inflated are re-inflated. When the damaged cord tears, opening a zipper-like rupture around the shoulder of the tire, anyone nearby can be seriously injured.

Air is part of the structure of the tire, just as rubber and steel wire are. Air stiffens the tire, and helps control tire flexing. Without enough air, tires flex excessively. As they do, steel and rubber heat up due to the internal friction. If enough heat builds up, internal temperatures in a tire can reach the point where rubber liquefies. When that happens, the bonds holding the tire together are destroyed. The result is the all-too-familiar "gator tail" along the roadside. Studies show most tires burst from low pressure, not from poorly done recapping.

Going by the book, we're supposed to gauge our tires daily – a task that can take up to 20 minutes. In many cases that just doesn't happen, even though it should. Luckily, there are devices to help us maintain tire pressures. They range from simple optical devices to complex computerized machines. Here's a brief rundown of what's available:

Pressure equalizing valves

The most basic aid is a dual inflation and pressure equalizing valve, essentially a hose and valve arrangement that interconnects dual tires. There is only one inflation valve per set of duals, not two. Both tires stay at the same pressure, unless one has a catastrophic failure. Then, the blown tire is isolated and pressure is retained in the good tire. The Crossfire, made by Dual Dynamic, is a well-known example of these types of devices. Link Manufacturing makes the unique Cat's Eye tire monitor. It links two tires, and provides an instant visual read-out of tire pressure.

Tire inflation systems

Central tire inflation systems are made by CM Automotive Systems and by Eaton. They are used effectively on military vehicles to adjust tire pressures to conditions, such as mud, snow and sand. Although available commercially, they are still quite pricey. One device currently available for trailers is from P.S.I., Pressure Systems International. It maintains air in trailer tires, even if a tire is cut or punctured. Since the ATIS (for Automatic Tire Inflation System) gets its air from the truck's compressed air system, full pressure will be maintained as long as the engine is running. Even after a prolonged shut-down, a deflated tire will be re-inflated by the ATIS. The unit activates automatically when air pressure drops. It lights a warning light at the front of the trailer, easily seen through the mirrors, to alert the driver.

Cycloid makes a wheel-mounted air pump that delivers enough air to maintain inflation pressure, but only while the wheels are rolling

For steer and drive tires, Cycloid makes a wheel-mounted air pump that delivers enough air to maintain inflation pressure, but only while the wheels are rolling. These units can also be mounted on trailer wheels.

Electronic innovations

For those who love electronics, and want to check all tires at one glance, Fleet Specialities Division makes the Tire Sentry. They use sensors in the valve caps. They continuously monitor pressure in each tire and, powered by ordinary watch batteries, send a radio signal if a tire drops below its normal operating level. Sensors are ordered preset to various pressures. They can be vehicle specific, transmitting a signal that can only be read by one rig, or fleet specific, so a trailer can be read by any fleet tractor pulling it. All sensors are position specific, so the dashboard-mounted gauge can identify which specific tire is low. The information is immediate, but the driver must act on it.

Tire manufacturers have all been developing tires with radio transmitting chips embedded inside. The chips will not only monitor pressure, but check temperature as well, and store all abnormalities in memory. When activated by maintenance technicians or by re-treaders, the chips will reveal any conditions which may leave a tire weakened or unfit for further use.

No matter which aids you use, from monitoring to automatic inflation, attention to tire pressures will pay dividends. New and re-treaded tires will last longer, tire casings will stay re-treadable longer, road service calls will be reduced, and fuel mileage will improve. LL