Tire Pressure/TPMS

[Jerry Emert]

With the Beaver Accident thread still going I have a question based on TPMS.  When I first bought our PT the ride was pretty harsh.  There were a bunch of things I didn't know at the time about the suspension, air leveling, the SMC leveling and tire pressure. I had 120 psi in all 8 tires, the hydraulic levelers up-down or wherever half the time and at one point my air leveling was on while going down the interstate at 70mph.  Ride was harsh to the point of bouncing me literally off my seat on I-95 in Florida (air leveling on, what a ride.)  I've since figured most of this stuff out.  Someone somewhere has messed with the wiring in my PT.  The cruise won't work unless the Jake is on.  The air leveling will engage while driving down the road, same for the SMC leveling.  OK, I know all this stuff now and know how to set tire inflation by 4 corner weight ideally.  Still never had the chance to get a 4 corner but have weighed at CAT scales.

Four years of ownership and my ride is now very good as far as I know since I've never driven another Class A.  The one area that still bugs me is tire inflation.  Based on coach weight I now run 115 on fronts, 100 on tags and 110 on rear duals.  I have had the EEZRV TPMS for 3 years. 

Now the point/question of my post.  As I understand it, if tire pressure is low, the side walls flex too much and the tire will heat up and at some point you would be in danger of the tire blowing.  I am probably not as good about filling tires as I should be.  They can get down 10 lbs before I'll get around to filling them.  The reason I've felt safe is that I monitor the TPMS constantly.  Tire temps stay virtually the same when a little low as they do when at the correct pressure.  Temps are usually about 10-15 degrees over ambient temps. when driving even in summer time Florida.   You all know how the other forums are, if your pressure is off by one lb, all eight tires are going to explode and you will fall off a mountain!!  Should I be agonizing over tire pressure and topping them off when they lose a pound or 3?  Just how much do we rely on our TPMS? Thanks for your patience.
Jerry

[Mike Shumack]

Hi Jerry,
I just posted on this subject in the "accident thread" here -- but to summarize;

In my experience/understanding of tire pressures, the important thing to know is that the tire pressure is not "low" if it is set at the tire manufacturer's recommendation for the weight carried by the tire. Meaning just being under 120 psi does not mean one is low. Tire pressures could be set to 75 or 85 psi and that would not be low (depending on the actual weight on tire and as given in the chart below).

Where "low" comes into play in my mind, is when the tire pressure is below the tire manufacture's recommendation for the weight it's carrying. That's why it is important to get the coach weighed. If you have not weighed the coach yet (I fall into that group myself) then set the tire pressure for the maximum axle capacity (GAWR).

Tire manufactures also add in a safety margin to their pressure charts. They know the tire will at times be run low on air, as air normally leaks out of the tire over time. So if they say run it at 100 psi they have calculated that you will be running at 95 psi at some point. I don't know what the safety margin is - but I feel confident that 5 psi under is not going to be a problem. And with the TPS monitoring we should not be running under the recommended pressure for very long anyways.


BTW - the "Smart Weigh" facility in Bushnell FL is reopening 10/15. Maybe you and I can meet up there one day (I plan to drive down and spend the night at their campground, and get the four corner weighing) and compare notes. https://www.escapees.com/education/smartweigh/

[David T. Richelderfer]

I check our tires' air pressures with a hand-held, digital gauge about once every week while traveling, or if there is a substantial temperature/altitude change.  If we have been parked for more than a week, then I check the tires before any trip.  I always check the tires early in the morning - usually at the coolest time of day.  I fill them to my checkpoints - 125 front, 115 duals, 110 tags - if they are down more than 2 or so pounds.

We have the Pressure Pro TPMS for all 12 tires - 8 on the coach and 4 on the pickup in tow.  I mostly keep the Silverleaf screen on the tire pressures while traveling.  The screen rotates through all 12 tires in series about every minute.  I periodically change the screen to the rear camera for a few moments to check on the pickup in tow, then change the screen back to the TPMS tire pressures.  Typically, our tire pressures increase from 10 to 15+ pounds from heat after 30 to 60 minutes on the road.

We have 315/80R22.5 tires on the front axle and 295/80R22.5 tires on the dual and tag axles with 9" wide rims all around.  To help reduce weight on the front axle, we reduced the tag axle downward pressure from 35ish to under 30ish pounds.

[Dale Walker]

I check the tire pressures every time I stop, for the dog, or fuel, or just to relax for a couple minutes. I found and installed tire safety caps. I had a TPM, but didn't like the fact that it couldn't be trusted. It would tell me a tire was low, but when I stopped to check it it would be alright. I found these on their website, http://www.accu-pressure.com/eShop/index.php . They come in 10 lb. increments, you can check them at every stop, in a walk around.

[George Frudakis]

Are these tire pressure cap relay working? it seems a better deal the TMP. I run 105 in the front and 110 in the rear. Do they come in 5 psi increments?
george

[Mike Shumack]

Yes they are available in 5 psi increments. https://www.amazon.com/Quick-Pressure-QP-000110-Chrome-Monitoring/dp/B00XCOQPZK/ref=sr_1_7?ie=UTF8&qid=1538129627&sr=8-7&keywords=tire+air+pressure+monitoring+caps

The problem with the caps is that if you run over something and get a small puncture, you would not know your losing air until it gets low enough to feel or until you stop and check the caps. With a TPS you would get an alarm in the coach once the pressure drops to the set "low pressure" alarm point.

[Jerry Emert]

George, I agree with Mike.  I don't use my TPMS as much to check the daily pressure in the tires as much as I count on the system to warn me if the tire temp goes too high or the pressure starts to go low.  The working tire pressure is nice but not nearly as necessary in my mind.

[Robin Goffrier]

I use a TPMS but mostly to prevent surprises going down the road.  As the mornings get colder my pressure alarms always howl when i turn on the system prior to departure.  Schwab told me not to add air in the mornings to correct a 4 0r 5 pound low alarm because as the tire warms up the pressure will return to non-alarm status, and it does.  My system is effective when there's leak  It has warned me twice of nail punctures resulting in slow leaks, However i find that to get accurate pressure readings i must chek the tires manually.

[Michael Peters]

I use the Pressure Pro TPMS. Have for 6 years . Replaced all sensors after 5 years. I was getting unreliable readings. At every startup I cycle thru all tires and check pressures. I run 120 psi front ,110 psi rear. I inflate my tires with CO2. I carry a small bottle that takes just minutes to grab and top off tires. The conveniece factor of 500 psi + to air up can't be beat. I don't remember what the original cost of bottle was , but refill/exchange run $25. I feel its very important to run tires at max psi for tire life.