Ahh the excitement and anticipation of buying your first
fiberglass camper! It seems that a common activity for those experiencing this anticipation is the shopping spree. What to buy? Maybe a patio mat? How about custom curtains? Its fun to plan and think about all the little things that will make your new home-away-from-home uniquely yours, and it helps to make the waiting more tolerable.
But after you have your wish list completed with the essentials, I personally feel that
a Tire Pressure Monitoring System (TPMS) should be on your list well ahead of the other “nice to have” items. A tire failure can do a lot of damage to the body of a
fiberglass trailer as well as the wiring,
propane and plumbing lines that run near the wheel well. A TPMS provides an added margin of safety on the road, and reduces the chance of having a tire failure causing hundreds, if not thousands, of dollars of damage or personal injury.
There are quite a few choices when it comes to a TPMS. I’ll share some of what I have learned and experienced with my TST 507 TPMS.
A good TPMS is not cheap, but IMHO it is something you should not scrimp on. TST (Truck System Technologies) is a well know company with a good track record. There are other brands that are cheaper but from what I have seen, none of the cheap brands have very good ratings. Therefore I will discuss the TST brand of TMPS.
At present, all of the TST kits include four or more sensors except for one, this
510 model which includes two sensors, the display, charger and a remote antenna. It is $205.95 shipped (to CONUS I assume).
However I have confirmed that you can buy the displays (with a charger cord included) and the sensors separately, and get a working 507 system for two wheels for as little as $175.95 with shipping included. Or get a color 507 model display for $30 more.
EDIT! See next message which mentions an even better deal from a reliable seller: http://perfectcasita.com/tst507stkit.html
With a TST system, you have two primary choices:
1. Cap type or flow through sensors, and 2. User replaceable sensor
battery or not.
Cap type vs. flow through sensors
The flow-though sensors allow you to add air to a tire without removing the sensor. A cap sensor is like the valve stem cap you already have, in that it must be removed to add air. The cap sensor has an anti-theft design that requires a special tool (included in the kits) to remove it from the valve. However the anti-theft housing can be removed by the user and the cap sensor used without it. In this case the sensor simply unscrews from the valve. This is what I have done and it works well for me since I am frequently adjusting air pressure. Of course there is a small risk of the sensor being stolen and they cost $50 each to replace. The flow-through sensor uses a small allen screw on the valve stem to discourage theft.
The cap sensor is smaller and about one quarter of an ounce lighter than the flow-through sensor. For most
fiberglass camper trailers I would think the cap sensor is the better choice. A flow-through sensor would be preferred when you have wheel covers or something else that makes it hard to get to the sensor to remove it.
Sensor battery, user replaceable or not?
507 series use sensors either with user replaceable batteries or with sealed batteries. The 510 series only uses sealed
battery sensors. The user replaceable models have a battery life of 1 to 1.5 years - you should plan on annual replacement. The CR-1632 button batteries are about $4 each. You should also replace an o-ring at the same time. A number of spare o-rings came with my kit but if you need more TST also sells a six-sensor o-ring rebuild kit for $7 not including shipping, or kits with o-rings and batteries are available on Amazon, etc. The batteries in sealed sensors should last 3-5 years at which time you send them back to TST for replacement at a cost of $29.95 per sensor.
A video of the battery replacement procedure is on the
TST Support page. If the replacement looks difficult to you then I would suggest the sealed version.
By the way, there is also a smaller rubber washer that goes inside the valve side of the sensor to seal the connection. Eventually these need to be replaced but they should last a few years at least. You will know they need to be replaced when air
leaks after the sensor is installed on the valve stem, or if it appears degraded.
How the TST systems work
Everything you need to know is on the
TST web site, but here is a brief summary:
The display has an internal battery and can be recharged or run from the cigarette lighter outlet. Battery life is very good and I have used my display for many days before it needed recharging.
After each sensor is paired to the display, the sensors will transmit the current pressure and temperature to the display. To conserve battery life, the sensor only transmits once every five minutes unless there is a fast leak in which case it transmits immediately. Exactly how much of a change, or how fast it has to be, to trigger an immediate transmission does not seem to be defined, but I do see that the display alarms within one to two seconds when I remove the sensor (dropping the pressure almost instantly to zero).
So every five minutes you get an updated pressure and temperature reading on the display. After setting up high and low pressure and high temperature limits, the unit will alarm if it receives a reading that violates the programmed parameters. The alarm is also audible so there is no need to have the display where you can see it if you are worried about being distracted. Claimed accuracy of the sensors is +/- 3 PSI.
A TPMS might not save you from damage from a sudden and complete blowout, but I read about people who had a complete tire failure on their trailer and did not even realize it. The alarm on a TST system would be impossible to miss however.
There are repeaters available for both 507 and 510 systems that relay and amplify the signal. These are almost never needed for small trailers.
Some of the sensors are listed for use with either rubber or metal valve stems, and some require metal valve stems only. In my opinion you should only use metal valve stems with stem mounted sensors. I have seen at least one case where a rubber valve stem cracked and leaked air, due perhaps to age, the
weight of the sensor, or both. The metal valve stems are only a few dollars and Discount Tire even installed mine at no charge. It is even possible that the temperature readings are more accurate with metal valve stems.
By the way, you may be asking yourself if you are going to unmount the tire anyway to install the metal valve stems, then why not install an internal pressure sensor like those on modern cars. That would be a good topic of discussion if anyone has experience doing it that way.
Now if you have read this far you are probably considering a TPMS but maybe still concerned about the price. I saw this
$100 TPMS for motorcycles on Amazon that has fairly good reviews and might work well (except for the receiver mounting, and apparently a lack of customer service). I’m not endorsing it since I have never owned one.
Before I had a TPMS I would always check the tire pressure in the morning before heading out, but then after a few miles I started to wonder if ran over some road debris, or had a bad tire, and the tire was leaking air, heating up and going to fail. Having the TPMS is great comfort where I can see that the pressure is normal. By the way, normal includes the pressure usually increasing a little, sometimes up to ten to twelve percent above cold inflation. The temperature can also increase quite a bit, especially when the tire is in the sun, but with the TPMS I can see the temperature lower again after a short time in the shade. After a while you get a feel for what readings are normal.
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Disclaimer: I have no connection to any company mentioned other than owning a TST 507 system. I have prepared this information because I believe this is a valuable tool which should be used by all fiberglass R/V owners. I have endeavored to provide accurate information but take no responsibility for inaccuracies or anything else related to this post.