Constant, real time tire pressure monitoring: hopefully improved blowout protection

[RockyMtnRay]

One of my biggest worries when towing is having a blowout on a trailer tire. Not only do blowouts cause substantial delay but if the streetside tire is the one that blows, there's a real good chance the disintegrating tire will severely damage the drain pipes. And a blowout on either side can do substantial damage to the floor and even innards of the trailer. And worse yet, about 60% of my towing is over narrow secondary and even tertiary highways that usually have absolutely no shoulder to pull off on...and turnoffs/driveways are often miles apart!

So I glean everything I can about trailer tire blowouts. It seems the consensus among tire experts is that about 90% of all blowouts are due to underinflation. The underinflation can be just plain low pressure or insufficient inflation for the load being carried. The other 10% are often attributed to tire oxidation (aka dry rot), road damage to the tire structure, or sometimes just plain loss of strength due to high mileage. Good storage practices, avoiding road damage as much as possible and replacing the tires every 5 to 7 years, apparently go a long way to prevent the non-underinflation causes. And I do all this, including storing the trailer inside my garage and taking the trailer's weight off the tires during storage (so there won't be a sidewall bulge during storage).

And I keep my trailer tires inflated to exactly 50 psi and check that pressure at the start of every towing day. But so do a goodly number of other folks...and many, like our member/moderator Bill...have had blowouts nonetheless. And more importantly, apparently many of those blowouts occurred with a very hot, probably severely underinflated tire: the clue is the mention of substantial amounts of rubber that were very firmly stuck to the trailer from the blowout. IMO, the only way that rubber is going to stick to the trailer's skin that firmly is if it was nearly molten when the tire disintegrated.

My conclusion is a tire that blows from underinflation yet was properly inflated at the start of that day had to suffer some kind of damage that started a leak. And all it would take is to run over a sharp object...nail, piece of junk metal, etc. And I further concluded the way to prevent a underinflation caused blowout resulting from a leaking tire was to install a system that constantly monitors the pressure in both trailer tires and instantly reports a pressure drop, even small, to a monitor in my truck's cab.

So I invested in a tire pressure monitoring system from Doran Pressure Pro . For $290, I got the system monitor and 2 sensors for my trailer's tires (the monitor can handle up to 16 sensors so I could add additional sensors for my truck's tires whenever I want to...additional sensors are $50 each). In a nutshell, the system works as follows:

• Each sensor sends a coded signal; during setup of the system you correlate a given sensor with a tire position on your rig. If there's a pressure loss, the monitor will identify which tire has the problem.
• When you screw the sensor on the valve stem, the pressure it records at that moment is its baseline pressure. As long as the pressure does not drop more than 12.5% below that baseline, the sensor sends out a pressure report about every 5 minutes. You can therefore get a reasonably current (within 5 minutes) display of each trailer tire's pressure at any time by pressing the up/down buttons on the monitor. Good for piece of mind...and pretty much precludes having to actually check the pressure of each trailer tire with a gauge every morning.
• If any tire's pressure drops 12.5% or more below the baseline, the sensor on that tire starts sending out signals every second or so...and the monitor displays a warning light and emits a warning sound. If the pressure drops 25% or more below the baseline, the monitor emits more urgent warnings. Clearly the smart thing to do is to get pulled off the road ASAP after the first warning sounds.

After using the system for about 1200 towing miles, I'm very happy with it even though there have been no pressure losses from my trailer tires. It's quite interesting to monitor the tire pressure changes that come from both changes in air temperature during the day as well as the temperature changes from towing speed changes (e.g. going from 50 mph to 65 mph seems to cause about a 2 psi increase in pressure). Although the sensors weigh about 2/3 of an ounce...and I did not have the tires rebalanced to accommodate that weight...I've had no indications of imbalanced tires. About the only effect I'm seeing is that the sensors are slightly bending the rubber valve stems at speed...you can see rub marks from the sensors on the wheel rims in the photos below.

Pictures:

• Pic of the monitor sitting on my truck's console...it's about the size of a typical rear view mirror. When towing, I usually just put the monitor on the console; when not towing I stow it inside the console's bin.
• Closeup pic of the monitor after I pushed a button to cause a pressure display of one tire's pressure. The tire being checked had a pressure of exactly 50 psi that morning (at a temperature of 70 degrees); after a few miles of towing (at ~45 mph) on a 90 degree day, the pressure rose to the displayed 54 psi.
• Pic of one of the sensors relative to the whole wheel.
• Closeup pic of the sensor. I put the label on the sensor so I know which tire it's associated with in the monitor. To increase sensor battery life, I plan to remove the sensors during winter storage...if they're not detecting any tire pressure, they stop transmitting.

Any questions???

[MikeD]

Ray,

I have come to the same conclusion as you did vis-a-vis probable cause for blow-outs, and so we also invested in a Doran Pressure Monitor. I have only been using it for about 100 miles, but my experience is like yours - easy to install, easy to use, and a great early warning system. I was very pleased that the monitor could be mounted cleanly in my cab, and still reliably receive the sensor signals. Apparently some other systems may need an external antenna. Since the tires are small and relatively light, I had my tires rebalanced after adding the sensor. Both wheels required a weight placed opposite of the sensor.

So far a happy customer.

MikeD

pleased to hear about the doran system... i've been using the pressure
tire caps (65psi) on my 3124kb trailer and they seem to work...i generally
check the indicators on the caps whenever i stop...however, your system
gives you a full time reading....i'm sure we are going to the full time system
soon...we are very concerned about blowouts ...sometime ago,i installed
truck tire mudflaps in hopes of protecting the plumbing etc....i even plan to
reenforce the street side mudflap with some steel....
thanks for your input on the doran system...
bill s

[tucsoncarol]

Two years ago my hubby and I took a trailerload of adoption bound greyhounds from Tucson to Coeur d'Alene in 24 hours. An exhausting trip and nerve wracking (the dogs are not well protected and suffer from changes in temperature). The trailer is very similar to a long TM in size. I was driving on the freeway in downtown Salt Lake City during rush hour at 75 mph when one of our tires blew. HOLY COW. My first concern, after limping off the freeway, was that none of the dogs were hurt by flying belts or chunks of rubber. We changed the tire easily enough, and were on our way. I learned two things. The people in Salt Lake City are generous to a fault, and I NEVER want to go through that again. Thank you Ray for the innovative ideas and the precision of your tutorials (plus great pics). I will be doing this upgrade.

If I understand you correctly, if your tire pressure drops from 50 psi cold to 44 psi hot then this is considered normal, less than a 12.5 percent decrease.

It seems to me that the range is a little high to truly be helpful.

Now if it would detect the normal increase in pressure as the tire gets hot and establish this higher pressure as the baseline then a decrease of 12.5 percent might be worth knowing about.

But I look forward to subsequent reports.

[MikeD]

Your understanding is correct. The reason I feel that this is useful are:

1. A leaking tire will probably continue to leak, so you will be notified.

2. You can easily check the tire pressure from the cab. This makes it very simple to do before leaving from a stop. The pressure should be at the cold point or higher and both tires shold be at approximately the same pressure. This makes it easy to check pressure during the trip and detect a problem before the alarm goes off.

3. If you look at the load inflation tables for the ST215/75R14 (my tires) at http://www.goodyear.com/rv/pdf/rv_inflation.pdf, you can see that the tire is down to a load of 1790 (loss of 80 lbs capacity) at 45 psi, and 1660 lbs (loss of 210 lbs) at 40 psi. I extrapolated that the load carrying capacity would still be about 1700lbs at 43 psi (I know it's not linear, but that's why I choose 43psi rather than 43.75psi). While not good for the tire, I assumed the tire would hold out for a while (at least until the lowering pressure triggered the alarm).

No perfect answers, but I believe that combining easy checking at each stop with the alarm function will give me a better chance at avoiding low pressure induced blow-outs.

MikeD

Now if you could just pump them up from the driver's seat like the trucks I used to work on in the Air Force! That would be great! I like the idea of being able to monitor the pressure, too.

[RockyMtnRay]

Originally Posted by MikeD

Your understanding is correct. The reason I feel that this is useful are:

1. A leaking tire will probably continue to leak, so you will be notified.

2. You can easily check the tire pressure from the cab. This makes it very simple to do before leaving from a stop. The pressure should be at the cold point or higher and both tires shold be at approximately the same pressure. This makes it easy to check pressure during the trip and detect a problem before the alarm goes off.

3. If you look at the load inflation tables for the ST215/75R14 (my tires) at http://www.goodyear.com/rv/pdf/rv_inflation.pdf, you can see that the tire is down to a load of 1790 (loss of 80 lbs capacity) at 45 psi, and 1660 lbs (loss of 210 lbs) at 40 psi. I extrapolated that the load carrying capacity would still be about 1700lbs at 43 psi (I know it's not linear, but that's why I choose 43psi rather than 43.75psi). While not good for the tire, I assumed the tire would hold out for a while (at least until the lowering pressure triggered the alarm).

No perfect answers, but I believe that combining easy checking at each stop with the alarm function will give me a better chance at avoiding low pressure induced blow-outs.

MikeD

Only thing I'd add is that you don't have to wait until a stop to do a pressure check...you can check the tire pressures on trailer whenever you want to. I do it anytime I think something doesn't quite feel "right"...and sometimes if I just get bored. . As noted earlier, unless the tire has lost more than 12.5% of the baseline pressure, the "current" pressure shown won't be more than 5 minutes out of date. If any tire has dropped more than 12.5% below the baseline, the pressure shown is current to the nearest second of time.

But since the cold starting pressure is almost always going to be the lowest of the day, any pressure seen below that start pressure on a random check means a problem!

[mjlaupp]

re: RMR picture #4.
I have had at least 4 tires loose pressure due to a cracked valve stem over the last 15 years. 2 were on a minivan with extra long stems to extend past full wire wheel covers. The other 2 were on an Isuzu Trooper II. These had heavy chrome plated valve caps installed. All of the failures were at or just outboard of the valve stem hole in the wheel. I don't know if they failed due to age or constant flexing. Suggest adding a valve stem check on a regular basis.
Mike

[RockyMtnRay]

Originally Posted by mjlaupp

re: RMR picture #4.
I have had at least 4 tires loose pressure due to a cracked valve stem over the last 15 years. 2 were on a minivan with extra long stems to extend past full wire wheel covers. The other 2 were on an Isuzu Trooper II. These had heavy chrome plated valve caps installed. All of the failures were at or just outboard of the valve stem hole in the wheel. I don't know if they failed due to age or constant flexing. Suggest adding a valve stem check on a regular basis.
Mike

Ah...you've identified the achilles heel of this system...flexing/stress on the rubber valve stems from the extra weight on the end of the stems.

Although a visual/manual valve stem check is certainly a good idea, these pressure sensors will automatically detect (and warn if it gets large enough) any pressure loss due to cracked valve stems. So I'm not at all concerned that the kind of pressure loss you had will go undetected. Kind of a dual edged sword...the sensors may accelerate deterioration of the rubber stems but they'll also immediately send a warning if the deterioration results in a significant pressure loss.

That being said, if/when a rubber valve stem does crack and start leaking, it could be a serious problem. My stems are currently in excellent condition...zero weathering and the rubber is very supple. And I've got only 2 more trips this year...around 800 miles total...I'd be really surprised if these stems couldn't last at least that long. Nonetheless, I'm planning on replacing the rubber stems with metal ones at the beginning of next year's towing season.