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Tire Pressure Monitoring Systems

UPDATED 7/26/2011:
I purchased a TPMS in early February 2010 but when it arrived I found it had to be mounted INSIDE the tire rim. I wanted a system with the sensors on the valve stems so I returned that system and we went to the Orlando HamCation without a TPMS. Ironically, we had a blowout on the trailer leaving Orlando. I have now purchased the $229 4 tire system from Truck System Technologies (Camping World sells this system but at a significantly higher price) and have found it to be very comforting.

I have programmed my monitor/display to show only the 4 trailer tires in sequence. It displays the most recent data from each sensor for 5 seconds (pressure and temp) then moves on to the next sensor. Each sensor transmits an updated pressure and temp reading at approximately 5 minute intervals, or immediately if there is any rapid change in pressure. There is a lot of debate on various forums regarding the accuracy and value of various TPMS temperature monitoring methods. Since this one is mounted on the valve stem it can only measure the temperature of the stem - however since the valve stem is metal and in contact with the rim I think it is a reliable temperature indicator. It definitely measures a significant difference in temperature when the trailer is in motion as opposed to when it has been sitting idle all day.
UPDATE: After using this unit for over a year I believe the temperature readings are reasonably accurate. The readings when parked seem to be within a few degrees of the temperature measured on an outdoor thermometer. When on the road for a long drive the readings seem to be typically in the 95 degree range when the outside temperature is comfortable, and will get over 100 when the outside temp is high. The temperature also seems to increase with speed - being higher on interstate highways than it is on stop and go roads.

I have not been able to get the monitor to shut off automatically. It is supposed to sense motion/vibration and turn off when the vehicle is still for more than a few minutes, but my monitor does not seem to shut off so I have remember to manually turn the monitor off.
UPDATE: After discussing this with the dealer I found that I had not interpreted the user manual correctly. The motion/vibration control is documented to function only when the monitor is running on internal batteries. If the power cord is plugged into the accessory jack the monitor stays on until you turn it off. I also have learned that the vibration sensor is very sensitive and thunder, or even high winds can trigger it to turn on.

Also there is no loss-of-signal indication. If I disconnect the trailer and drive off for the day, the display still shows the last pressure reading until I force a reset by turning the monitor off and back on. So, if a sensor fails, or flies off of the rim, there will be no indication of a problem on the monitor. I spoke with the TST manager about this and he indicated it was on the list of improvements for the next version/model.

I will continue to update this page based on my experiences.
Any additional information or comments are welcome.
Thanks, K4HM - Hank

The information below was collected in early 2010.

Tire Rack This site has a lot of general Information about TPMS systems.
They also sell several brands of TPMS.
Orange Electronic TPMS System Has good reviews and is the least expensive I found. Alarm points set by user.
Sensor mounts INSIDE the rim. For use with max tire pressure of 60psi.
HawksHead 2nd lowest price I found. Includes temperature monitoring.
Pressure alarms preset at 12.5% drop and 25% drop.
Truck System Technologies Good price system pacckages for 2 - 22 wheels. Includes temperature monitoring. This is one of the systems sold by Camping World but direct purchase beats CW member price by mucho $. System can be expanded by simply adding more sensors. They recommend using metal valve stems.
Doran Many options, but none have temperature monitoring.
PressurePro Probably the best known but is expensive and has no temperature monitoring.
TireStat More expensive, air up without removing sensors, requires metal stems, programmable alarms.
SmarTire Dealer installed only - requires tire removal and valve replacement.
This system is "Smart" because it adjusts the alram level to compensate for tire temperature.