My canned thoughts on using a Tire Pressure Monitoring System (TPMS) on a trailer (the advice is a bit different for a motorhome):
- A TPMS on a trailer, while towing, should be considered more of a trend monitor. In other words, if all of the tires are behaving essentially the same and all of the tires are behaving essentially as you know they have in the past, the absolute numbers AND how much they change while towing are not that important.
Note that the direct sun on one side will raise the temps and pressures of those tires, more than you might expect. You can even see this effect while parked. That's why tires must have their pressure set while "cold".
"Cold" means "Today's outside air temperature BEFORE the tires have been used and BEFORE the direct sun has a chance to warm the tires."
- WHY YOU SEE PRESSURE INCREASES WHILE TOWING - As long as the cold pressure is set appropriately for the weight, and for a trailer with more than one tire on each side that almost always should be the pressure molded into the sidewall due to interply shear stresses, any pressure increase while traveling is pretty much irrelevant UNLESS the tire is overloaded OR a mechanical failure is occurring, such as a wheel bearing failing. A failing wheel bearing will cause the tire to heat up because the tire cannot spin as freely. That temperature increase will also cause some increase in the tire pressure.
Why are pressure increases normally not a concern while underway? Because the tires are designed to easily handle those pressure increases as long as the tires are not overloaded. The pressure increases are normal and they are expected.
The pressure molded into the tire sidewall is a constant source of confusion. It is NOT the maximum pressure the tire should ever see.
That molded pressure is the MINIMUM air pressure needed in the tire to safely support the MAXIMUM weight that the tire is designed for WHEN COLD.
- WHY YOU SEE TEMPERATURE INCREASES WHILE TOWING - It's the same reason as above. When the tires are being used there is road friction and their temperature will go up, the same as how their pressure goes up. Also, the sun shining directly on one side will raise the pressure and temperatures on just those tires.
That being said, on a trailer, an abnormal TEMPERATURE increase might be indicative of a failing wheel bearing or a dragging brake. "Might" being the operative word.
THIS IS IMPORTANT -> If you do not already do so, consider buying an infrared temperature "gun" and get in the habit of "shooting" the wheel hub temperatures each time you stop, as soon as you stop because they can cool quickly. If one wheel hub is significantly hotter than the others you have a problem, perhaps a big problem.
- LOW PRESSURE ALARM - The critical alarm on a TPMS is the Low Pressure alarm.
A tire that is 20% below the required pressure is considered flat and subject to hidden damage.
The Low Pressure alarm should be set to no more than 10% below the required cold pressure to give you an adequate amount of time to get pulled over, add air to get to a tire shop, or whatever is needed.
So if your tires are supposed to be set cold to 65 PSI to handle the weight they're carrying, then the Low Pressure Alarm should be set to alarm at no less than 59 PSI and 52 PSI is considered flat. That's not much of a difference.
- HIGH TEMPERATURE alarm and HIGH PRESSURE ALARM - Because these are somewhat useful on a trailer, they should be set to something higher than you see while towing. I know, that's a somewhat useless answer.
Read the TPMS manual for suggestions.
In other words, you need to do some trips to know where they should alarm. For example, if the highest pressure you ever see on your 65 PSI tires is 80 PSI, you might consider setting the HIGH PRESSURE alarm to 85 or 90 PSI.
The key is to have the "HIGH" alarms set high enough that they will NEVER go off when nothing is wrong. I made that mistake once and trust me, it is not something you want to try to deal with at 65 MPH just to find out it was the hot sun that did it.
- Separate TPMS display or a phone app for the display? Do you really want a critical safety feature dependent on a phone being charged or on some phone update breaking the TPMS functionality? Not me but perhaps you are OK with that.
- Note that at least one TPMS manufacturer does NOT let the owner set their own alarm thresholds. They try to do your thinking for you by using a "percentage of baseline" for all alarms. When selecting a TPMS system be aware of that limitation. Personally, I would never buy that system but others like it.
- No, a TPMS is not cheap but it is cheap insurance and only has a one-time premium payment.
In most cases the price of a TPMS is less than the cost of one tire and much less than repairing the damage from a tire that disassembled itself at highway speeds.
And NEVER let air out of a hot tire. Never.
Make sense?
Ray
2011 Flagstaff 831 RLBSS
Linear Mode
