RV Modifications Part 1- Tire pressure monitor system

 October 20, 2021

RV Modifications Part 1- Tire pressure monitoring system

One of the most common disasters to befall RV owners is tire failures.  A tire blow-out can cause loss of control and a serious crash, and because RV’s are often operating at or near maximum weight ratings, the tires are under much more stress than passenger vehicle tires.  While tire pressure monitoring systems are mandated in all newer passenger vehicles, this is not the case with RV’s.  While a walk-around inspection before hitting the road can reveal an obviously flat tire in most vehicles, an RV with dual rear wheels, such as this class C Sprinter chassis based RV, has rear wheels that are not visible when you do a routine walk around.  If an inside tire develops a problem, it frequently deteriorates into a full on blow out, and the sudden load on the remaining tire can cause it to fail as well.

The best way to avoid a tire failure is to install a tire pressure monitor.  Fortunately, there are after market tire pressure monitoring systems that can be easily installed by most people with basic installation skills.  The cost of one of these systems can be less than the cost of a tire failure, especially if you include any emergency road side services in addition to the cost of the replacement tire and installation.  

After reading product reviews on the internet, we decided to install the Truck System Technologies (TST) model TM-507 wireless tire pressure monitor.  This can be bundled with as many sensors as needed to monitor not only the tires on the RV, but can also monitor the spare tire and tires on any tow-behind vehicles or trailers if you purchase additional sensors.  The in-cab display is simply plugged into a cigarette lighter for power, but uses a standard USB power input jack, so an in-cab USB port could also be used for power.  

The TM-507 came with a suction mount for dash and windshield mounting, as well as a rubber cradle mount.  I used the suction mount initially, but it had a tendency to fall off the windshield and dashboard after a while.  Fortunately, the RV’s original owner had included an adjustable cup holder smart phone mount that shared the same mounting frame on the back as the TM-507 has, so I was able to simply snap the TM-507 onto that adjustable cup holder mount.  I plugged it into the cigarette lighter below the center cup holders in the Sprinter cab.  The USB ports in this Sprinter chassis are all USB-C, while the USB power cord for the TM-507 is USB-A.  The TM-507 does come with a cigarette lighter USB-A power adapter.  

The TM-507 displays a graphical representation of the primary vehicle’s tire locations with accommodation for single front axles, and dually multiple rear axles, as well as wheel and axle indicators for towed vehicles and trailers.  It displays the temperature and air pressure for each wheel position as the wheel position indicator blinks.  You do have to watch it for a while to see it cycle through all of the wheel positions- in our particular case, there are six.  Each position is displayed for a couple of seconds before cycling to the next position.  But you don’t have to stare at the monitor to determine if there is a problem because the unit will sound an audible alarm and display the wheel locations with problems if pressure or temperature measurements are out of the normal ranges, which you can set for each axle.  

The drive side rear inside tire indicator is flashing and the display shows 55˚F and 61 PSI

Programming the sensors to the display does require reading the instructions and following the directions, but this is not particularly difficult.  However, when I first attempted to do this, the display did not respond like the instructions said it should have.  I called technical support and ended up exchanging the first unit I purchased for another one that did work as it should.  So they aren't 100% perfect, but they did stand behind the product, and with the replacement display, I had no trouble  programming in all the sensors and alarm values.  

The TM-507 also comes with a repeater transmitter that they recommend be installed somewhere in the undercarriage of the vehicle near the rear axle, but that did not prove necessary with our Winnebago View which is 25'-6" long.  I suspect that if we were towing a vehicle or trailer, the repeater should be installed below the rear bumper to pick up the signals from sensors on the towed vehicle or trailer.  The package we purchased came with six sensors that mount on the valve stems, and have through sensor air passages so the sensors don't have to be removed to add air to the tires.  

Installing the sensors on the front tires is simple.  They simply screw on to the end of the inflation stems, replacing the caps.  They do stick out a bit, but the wheel hubs on these stick out far enough that the sensors don't seem to be at much risk of getting damaged unless you go off roading.  

Installing the sensors on the rear tires requires a bit of knowledge and extra parts.  Because the rear wheels are mounted as duallies, the valve stems are not readily accessible.  This requires the addition of metal 3" straight valve stem extensions to the inside wheels, and 180˚ metal valve stem extensions for the outside wheels.  The inside wheel extensions are straight forward to install- simply remove the valve cap and screw on the extensions.  The tire pressure monitor sensors can then be simply screwed to the ends of these.  

But the outer wheels require some jury-rigging because the openings in the Alcoa forged aluminum wheels does not allow adequate clearance to install the 180˚ extensions and sensors.  I as unable to find any perfect extensions for this particular job, so I took the ones I purchased  from CampingWorld, put them in a vise, and bent the extensions so that the extensions were about 15˚ out of plane from the original "U" shape.  This allowed them to be installed through the wheel openings with one end firmly on the valve stem and the other end protruding through the wheel opening where the sensors could be attached to them.  The valve stem extensions should only be used with metal valve stems, which these wheels were originally equipped with.  

The TM-507 has a built in rechargeable battery for maintaining memory settings for the sensors and alarm levels, but turns itself off after power is removed from the USB power port.  On this Sprinter chassis, the cigarette lighter is only powered up when the ignition is on, so it turns itself off and back on again with the ignition.  Once it powers up, it does take several minutes for the monitor to detect and sync with all of the sensor transmitters.  Each sensor probably only transmits briefly every couple of minutes to save on battery power.  These sensors contain user replaceable CR1632 lithium batteries which are supposed to last a couple of years.  Some competing tire pressure monitoring systems do not have user replaceable batteries and require the entire sensor be replaced when the battery dies, so this is a significant competitive advantage for the TM-507.  

So far, the system has been installed for nearly a year, and it has functioned flawlessly.  It has allowed us to detect even minor differences in tire pressures between the six wheels, and you can even see how the tire pressure can vary just because of the sunlight on one side of the vehicle vs the shady side.  Having the system installed gives us a greater deal of confidence in our RV travels, which allows us to relax and enjoy the ride all the more.  We would highly recommend installing a tire pressure monitoring system in any RV as the first or highest priority owner modification because of the safety it adds and relative ease of installation.