Alternative Choices
--B.S.
During the last few years there have been numerous direct and indirect TPMS available as aftermarket accessories, and, as you might expect, there is a considerable price range.
The chrome caps from Accu-Pressure Safety Caps, Inc., uses a spring-loaded pressure-activated bar to display green in their clear tops when tire pressure is adequate. When pressure drops 4 to 5 psi below normal the caps shows yellow and red when the tire pressure is 10 pounds below the cap's preset rating. The caps are sold in 2psi increments from 26-40 psi, then 44, 50, and 60 psi, and will cost less than $20.
Tire Sentry is a brand-new wireless monitoring system that uses advanced RF microchip technology mounted inside a replacement valve-stem cap, which continuously monitors tire pressure. A two-inch-diameter gauge on the dash alerts you when pressures fall below eight percent (2.5 psi) of the tire- pressure preset for the caps. Price for this kit, which should be available by late summer, is expected to be less than $350.
The system on my '02 Chevy TrailBlazer comes from Intellivalve and, like most of the new direct TPMS, it incorporates four individual wireless transmitters inside a small plastic housing attached to a chrome valve stem. Tire-pressure and heat readings are transmitted to a monitor inside the vehicle. This system warns you of either high or low tire pressures and temperatures. The out-of-the-box high setting is 35 psi, and the low, when warning sounds and light flashes, is 30 psi. The Intellivalve is distributed exclusively through PDK Wheels & Auto Accessories for $299.
For something more sophisticated, SmarTire, one of the first companies on the market, offers its GenII system with transmitters attached to the rims of a vehicle via a band. (It's worth noting, valve-stem-type sensors don't fit all OEM and aftermarket 18-inch and larger wheels.) A full-function display allows the driver to monitor temperatures and pressures of individual tires. Along with flashing lights and warning alarms, the GenII TPMS also incorporates battery-saving features such as transmitting normal tire pressures every four to six minutes as well as sleep modes when the vehicle is parked. Price is $300 for the full-function display; add $79 for dual-rear-wheel applications.
One of the more technologically advanced systems is the Cycloid Company AutoPump shown on the Jeep Grand Cherokee Concierge concept vehicle. The unit, about the size of a hockey puck, attaches to the outside of the wheel and automatically keeps the tire inflated to proper pressures. An in-vehicle monitor provides the driver with necessary tire-pressure information and warnings. The AutoPump isn't yet available for truck owners, but the company says it should be within the next two years for around $300.