Premature tire replacements cost construction contractors millions of dollars per year while wasting thousands of hours of valuable work time, but thanks to advances in technology and heavy investment by the military, help is on the way. After two decades of development, central tire inflation systems (CTIS) have been refined to a point of commercial viability.
An underinflated tire could lead to several disastrous effects. At worst, an underinflated tire can cause a blowout, posing a threat to operators and passengers in the vehicle and other drivers on the road. In addition, low tires decrease fuel efficiency, cargo capacity, and mileage, while increasing the replacement costs of tire casings that run hot. Properly inflated tires, however, improve vehicle handling and provide less damage to work sites and the environment (not leaving the deep grooves and ruts), while increasing rider comfort.
In normal conditions, tires lose 1 psi per month. For every 10ºF decrease, tires lose 1 psi as well. Given that pressure loss is a fact of life, routine checking and replenishment should solve underinflation problems, but this is much better in theory than in practice. Remarks Joe Tillis, tire/retread operations manager with Tomcar Industries Trucking, “Even with a shotgun to their head, you’re not going to get operators to check their tires.” But this makes sense if you look at human nature. After all, how can you expect an operator to check the tires of a vehicle that is not his? He often feels that this is a mechanic’s or some other operator’s responsibility.
A CTIS system, such as the one produced by P.S.I. International, works by attaching hoses between the vehicle’s air brakes and the trailer’s hollow axles that have been sealed off to become airtight (Figure 1). The hoses run through a control box that regulates air pressure in the tires. When the regulator detects low air pressure, air is transferred from the sealed-off axles to the low tire through a small rotational part on the axle. The system only allows air to go one way, preventing air from transferring from one tire to another, as in equalization systems. In addition, if a tire is in need of replacement from a puncture or a blowout, the system notifies the vehicle operator with a light on the radius of the trailer. According to Todd Cross, a regional sales manager with P.S.I., “It takes a person who’s never done it about four hours to retrofit the system.” If a contractor is purchasing a new vehicle, P.S.I.’s CTIS is an option at every trailer manufacturer. Priced at around $750, the system needs very little maintenance; every couple of years, the rotational part on the axle needs to be replaced (costing around $12).
Since tires are the second-largest financial expenditure for most fleets, a CTIS seems like a vital necessity for commercial vehicles. Tillis reports that Tomcar has a fleet of 12,500 vehicles, and more than 4,000 already have P.S.I.’s system. “Others are being retrofitted so that they can have inflation systems installed.” At around $750 for complete installation, Tillis emphasizes their economic viability, stating, “Replacing two tires on the road pays for the system. Over the years, we will also save millions on purchasing tire casings.”
Cherokee Waste, a garbage and sludge hauling company, has P.S.I.’s system on 80% of its trailers. President and Owner Henry Lee is ecstatic about his results with the CTIS, claiming, “It’s marvelous! It’s one of the few things that I have bought that actually works.” He adds that, since last June when he started purchasing trailers furnished with a CTIS, they have not had a single blowout. He also estimates that work has increased by at least 20% because “some operators get one extra load a day because they’re not on the side of the road [fixing a blowout] or wasting time checking air and filling tires.”
Traveling off-road to landfills, tires are exposed to uneven ground filled with debris and rocks. “I’ve brought a tire to the recap people with 32 nails in it,” Lee relates. And usually when one tire blows out, the tire adjacent to the flat can blowout easily from the increased pressure. This is a costly misfortune, Lee points out. “At $200 to $250 per tire, a blowout could cost $500. That’s not including the two hours spent fixing it. One blowout pays for the entire system. It is now standard equipment on all my new trailers.”
A System That Thinks for Itself
For fleets requiring an all-wheel-drive system, Dana Spicer offers an alternative in its Spicer Tire Pressure Control system (TPCS). This pressure control system, costing between $8,000 and $12,000, differs greatly from P.S.I.’s CTIS in that it inflates and deflates the tires according to travel conditions and speeds. At regular intervals (ranging from five to 15 minutes), the Spicer TPCS measures tire pressure in each axle group of the vehicle, including the steer, drive, and trailer. If a pressure change is necessary, the system either inflates or deflates the tires accordingly, notifying the operator through a control panel. The panel also provides the operator with a reading of the air pressure in each axle group. Gary Shultz, Dana Corporation’s product manager, states, “The Spicer Tire Pressure Control System eliminates the need for all-wheel drive by increasing the mobility of the vehicle.”
Tim Moore, fleet manager of maintenance at ready-mix company RMC Ewell Inc., explains the value of the TPCS in lieu of all-wheel drive: “It’s about $10,000 cheaper than an all-wheel-drive system, and it significantly lowers the weight of the vehicle. It makes a spec’ing job with weight restrictions a lot easier. I’ve seen a truck with the tire-pressure control system go where other all-wheel-drive vehicles start hopping. It’s just more component-friendly. If you can place concrete where other companies can’t, it gives you a competitive advantage.”
Schultz points out, “We have sold over 50,000 systems since the late 1980s. Over 5,000 systems were fielded in Desert Storm, with no reported failures. Most of the trucks returned with over 100,000 miles on the odometers.” The TPCS is designed to operate over the life of the vehicle. He expects the price to go down as the market for the system increases.
For exclusively off-road vehicles with enormously expensive tires, Bridgestone Firestone is working on a prototype tire monitoring system. B-F’s Jeff Asay explains that the monitoring system “will be geared for tires with as much as 57-inch rim sizes. Some of these tires can cost over $50,000.”
While tire inflation or pressure control systems are presently a luxury, vehicle manufacturers will be required to incorporate some sort of inboard tire inflation warning system by the year 2003. The Transportation Recall, Enhancement, Accountability, and Documentation Act (TREAD Act), signed by former President Clinton, calls for “a regulation to require a warning system in a motor vehicle to indicate to the operator when a tire is significantly under inflated.” Geared for passenger and commercial vehicles, such warning systems are likely to feature “idiot lights” that notify operators after tire pressure has fallen below a reference value, whereas a CTIS or TPCS takes a positive-action approach to ensure proper tire inflation.
