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Tuesday, August 1, 2017

How I program my TPMS

As you know I am a strong supporter of having all RVs being equipped with Tire Pressure Monitor Systems. Since 2004 cars and many pickups with ratings less than 10,000# GVWR have come with TPMS installed by the factory.

RV companies have not been providing TPMS even as optional equipment from the factory, so we owners have had to make the purchase and install the warning systems ourselves. This means we need to ensure the warning levels are appropriate for our RV.

While I can't address how to program every different type or brand system, I can tell you how I have the system I purchased set up. I hope that after reading this post you can sit down with the information that is specific to your RV,  i.e., load on each tire position, tire size, Load Range and inflation info, and ensure your settings are appropriate for your personal situation. So I suggest you dig out the instructions that came with your TPMS and review your settings.

First off, some terms:

MOP - Minimum Operating Pressure - This is the minimum pressure that I think you should ever operate your tires. This pressure is found in the Load/Pressure tables and is the minimum pressure needed to support the actual measured tire load.

CIP - Cold Inflation Pressure. This is the pressure you would set your tires to before driving on them. The tire should not be warmed by either driving on them or having the tire in direct sunlight for the previous two hours. Some folks call this their "Set Pressure" or "Baseline Pressure". I suggest the CIP be set to MOP + 10%, or +10 psi, but not to exceed the pressure molded on the tire sidewall associated with its max load, as this tire pressure may be the intended max CIP for the wheel.

Tire Load - This is the actual measured load on the tires when the RV is at the heaviest you would ever expect to be. Ideally this has been learned by having individual scales under each tire position on your RV. If you can't get this number then at least get the RV on a truck scale such as a CAT scale at a truck stop and learn the actual load on each axle. We want to know each tire position or each axle, as loads are almost never completely evenly distributed. It is not unusual to have tire on an axle or on one end of an axle to have 500# to 1,000# more than another position. There are a number of posts in this blog on load and how to get the loads on each tire position. Note duals are considered one position. If you can't get individual axle ends measured then I suggest you use the measured axle load and assume one end has 53% of the axle load. This would provide at least a partial margin for error.

Hot Running Inflation - This is the pressure we see on a tire after it has been running down the road. I have previously covered the relation between Temperature and pressure in THIS post. Normally for properly inflated tires this will be 10% to 20% above your CIP.


When I bought my Class-C unit in 2008 the first "add-on" was a TPMS. At the time I was not really aware of the selection of TPMS available for the RV aftermarket but I found a system made by German electronics company Hella. It was an internal system but it was designed for passenger cars so I had some problems as my hot tire pressures occasionally exceeded the high pressure warning level programed by Hella. I learned to ignore the occasional high pressure warning levels. In 2009 I started to go to FMCA RV conventions and rallies where I discovered the aftermarket systems designed for the RV use. Based on features I felt important, I purchased a TireTraker TPMS.
When we bought our new 2016 Class-C coach, I needed a new TPMS and selected the TireTraker TT500 as I felt the features plus the lifetime guarantee made it the best option available for me.

Programing the TPMS:
This is usually a two-step process. First, you need to have the monitor/display "learn" which sensor is on which tire. For the TT500 it involves stepping through the monitor settings, identifying a position and installing a sensor at the appropriate position. Other brand TPMSs may have different setup steps or even may come pre-programed with each sensor marked by position. It's the next step that I think is also important to get right for your specific needs.

Setting the warning levels:
Before we start the actual process of setting the levels, it is important to know what the various levels should be. You also need to know which pressure warning levels you can set and which may need extra work if you can't set the levels yourself. Again I can't address every brand TPMS so you may need to re-read your manual or even contact the support people at your brand TPMS.

1. Low Pressure warning level. Some systems have a fixed % below your baseline pressure; others may allow you to set this level independent of the CIP. You need to know how to set this level or what the % below the baseline your system works on. My TT500 is pre-programed to warn at -15% from the "Baseline" or CIP.

2. High Pressure warning level. The TireTraker is pre-programed at "Baseline" + 25%.

3. High Temperature level. The TireTraker, as are many TPMS, is set to warn of high temperature at the 70 C to 75 C (158 F to 167 F) range. IMO it should be remembered that it is low pressure that generated high tire temperature. If you get a High Temp warning but the pressure is OK, then your sensor has detected high temp from metal components that transfer heat faster than rubber. This might indicate a bearing or brake problem which should be checked as soon as possible.

Here things get a bit complex:
We do not want to operate tires when under-inflated but if we set the CIP or Baseline pressure to just what is needed to support the load the TPMS will not warn till we are 15% underinflated. If our CIP is MOP + 10% (See definition of MOP above) we still could end up with an underinflated tire. So to meet my goal of never operating in an underinflated condition, I will need to set my TPMS "Baseline" pressure to MOP + 15%.

My situation and solution:
As measured by RVSEF (RV Safety & Education Foundation):
My front tires are loaded LF 1,900#   RF 2,100#   and
Rear Duals  LR 3,550#   RR  3,850#
Tires are LT225/75R16 LR-E

Based on Load & Inflation tables for my size tires, my MOP for my front tires on my Class-C is 60 psi based on the 2,100 load and also happens to be 60 psi based on my read dual load of 3,850.

I add 10 psi to 60psi and get 70 psi for my CIP.

If I want my TPMS to warn me before I get to my MOP, I need to set the "Baseline" pressure on my TPMS to MOP + 15%, which for 60 psi is 9 psi. So in my case my "Baseline" for the TPMS and my CIP are within 1 psi of each other. I don't worry about trying to measure or set my tire pressures closer than +/- 1 psi. I would say that if you are within +/- 2 psi when setting your CIP you are in good shape.

We need to be careful when discussing safety margins or pressure changes as people with Load Range C, D and E tires will have different calculations than the folks with LR-G & H tires where 15% might be 18 psi.

The High Pressure warning level for TireTraker is Baseline +25%, so with a Baseline of 69 to 70 psi, that equates to 87 psi. On a recent trip to Indianapolis in the heat of the day I noted my tire pressure had gone up about 15%, so my settings worked out for me.

##RVT805













2 comments:

  1. We have a large Class A with Load Range H tires and have weighed each position to get accurate and actual weight. Our fronts by manufacturer tables and our actual weight call for 110 lbs - with tire maximum of 120 lbs - so we do not exceed manufacturers recommended pressure as we would then be risking over inflation.

    We use a digital tire pressure gauge to set pressure on each and every tire and compare our readings to our TPMS readings. By using the same tire pressure gauge on each tire I know I am getting the same pressure level - which does not always agree with the TPMS sensor. If my tire gauge says 110 psi my TPMS senors could read 108 on one side and 112 on the other. Now I know what my monitor should read when my tires are actually at 110 psi.

    I walk around our RV at least once a month with my monitor and unscrew each sensor to make sure the monitor goes immediately to zero and sets off the alarm. I then tighten the sensor to make sure it returns to the correct pressure reading. This checks the sensors and the batteries - and the tires - and the monitor.

    We just got 6 new tires at about $600 each plus balance, excise tax, sales tax, installation, old tire disposal fee, etc. Our TPMS is the best insurance we have to protect that investment - at about half the cost of one tire - not to mention the damage a flat tire can do to an RV when the rubber starts flying. A TPMS can save thousands. Basic common sense item.

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  2. Good idea to confirm all sensors will warn immediately when pressure drops. Yes Sensor readings can be different than a calibrated hand gauge. It is important to remember that TPMS are primarily a system to warn of pressure loss and are not a replacement for accurate hand digital gauges. You have some experience now so know your TPMS readings will have a range. I do suggest using the hand gauge when setting tire pressure.

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