Setting of TPMS Tire Pressure Alarm Points

[geofferyh]

I am hoping to get some discussion going with regard to setting of high and low tire pressure alarm points of a TPMS monitor.

Let me first state that we are usually advised to inflate and set tire pressure while tires are "cold"; which is generally meant to mean at the current outside ambient air temperature, and without direct exposure to the sun.

Tire manufactures emboss the tire side wall with a maximum load and maximum cold inflation pressure, like 110 psi, which I understand is generally defined to be at a 65° F ambient air temperature. Agree or Disagree?

Motorhome manufacturers apply a load factor rating sticker that outlines specific tires, like 235/80R22.5G, with recommended minimum inflation pressures like "Front Single Tires - 95 psi" and "Rear Dual Tires - 85 psi", which again may be generally defined to be at a 65° F ambient air temperature. Agree or Disagree?

However, tires are not always able to be inflated while at 65° F and the real situation is that tires do not maintain the initial "inflation" pressure while in service. The temperature of a tire in service is said to increase about 20% above the ambient air temperature (excluding any increases due to road temperatures and exposure to the sun) which causes the tire pressure to increase at around 0.7 psi per 10° F in temperature rise.

I have read that the general rule of thumb is to set TPMS pressure alarm points at 20% over and 10% under "cold inflation pressure". However, who's "cold inflation" parameter is the best guideline?

I would be inclined to set the TPMS tire pressure alarm points based on "tire operating pressure" as versus actual "tire inflation pressure", at some projected ambient air temperature, using the +20%/-10% psi rule.

I would really appreciate comment from those of you having experience with setting TPMS tire pressure alarm set points.

[hayward3411]

I purchased a set for a friends TT, the temperature setting was set at the recommended 158 degrees. While traveling to Virginia Beach a bearing failed if I had set the temp alarm a little lower it could of caught the bearing failure before it completely seized. I will do this next season.

[dabrooks]

Originally Posted by geofferyh

I am hoping to get some discussion going with regard to setting of high and low tire pressure alarm points of a TPMS monitor.

Let me first state that we are usually advised to inflate and set tire pressure while tires are "cold"; which is generally meant to mean at the current outside ambient air temperature, and without direct exposure to the sun.

Tire manufactures emboss the tire side wall with a maximum load and maximum cold inflation pressure, like 110 psi, which I understand is generally defined to be at a 65° F ambient air temperature. Agree or Disagree?

Motorhome manufacturers apply a load factor rating sticker that outlines specific tires, like 235/80R22.5G, with recommended minimum inflation pressures like "Front Single Tires - 95 psi" and "Rear Dual Tires - 85 psi", which again may be generally defined to be at a 65° F ambient air temperature. Agree or Disagree?

However, tires are not always able to be inflated while at 65° F and the real situation is that tires do not maintain the initial "inflation" pressure while in service. The temperature of a tire in service is said to increase about 20% above the ambient air temperature (excluding any increases due to road temperatures and exposure to the sun) which causes the tire pressure to increase at around 0.7 psi per 10° F in temperature rise.

I have read that the general rule of thumb is to set TPMS pressure alarm points at 20% over and 10% under "cold inflation pressure". However, who's "cold inflation" parameter is the best guideline?

I would be inclined to set the TPMS tire pressure alarm points based on "tire operating pressure" as versus actual "tire inflation pressure", at some projected ambient air temperature, using the +20%/-10% psi rule.

I would really appreciate comment from those of you having experience with setting TPMS tire pressure alarm set points.

I think if you set the low pressure alarm at 10% below the operating temperature you will get a lot of low pressure alarms on cool mornings.
I inflate the front tires to 85lbs when the temperature was around 70 degrees. After running a few miles on a 70 degree day the operating temperature will rise to between 80 to 85 degrees and the operating pressure will be about 92lbs. If I set the low alarm to 10% of that it would be about 83lbs. If I get up the next morning to leave and it is 55 to 60 degrees the low alarm would be going off because the tire pressures would probably be below 83 lbs. I think your idea of setting the low alarm based on the operating temperature does have some merit but I think 10% would be to low.

[geofferyh]

Originally Posted by hayward3411

I purchased a set for a friends TT, the temperature setting was set at the recommended 158 degrees. While traveling to Virginia Beach a bearing failed if I had set the temp alarm a little lower it could of caught the bearing failure before it completely seized. I will do this next season.

In that the high temp alarm setting is monitoring the air temperature inside the tire, I would question whether an overheated bearing would elevate the tire temperature high enough to trigger the alarm before the bearing seized. At what temperature would you set the TPMS alarm?

[geofferyh]

Originally Posted by dabrooks

I think if you set the low pressure alarm at 10% below the operating temperature you will get a lot of low pressure alarms on cool mornings.
I inflate the front tires to 85lbs when the temperature was around 70 degrees. After running a few miles on a 70 degree day the operating temperature will rise to between 80 to 85 degrees and the operating pressure will be about 92lbs. If I set the low alarm to 10% of that it would be about 83lbs. If I get up the next morning to leave and it is 55 to 60 degrees the low alarm would be going off because the tire pressures would probably be below 83 lbs. I think your idea of setting the low alarm based on the operating temperature does have some merit but I think 10% would be to low.

What brand and tire size are you running on the Tiffin? Also, what is the Tiffin recommended minimum tire inflation for your coach, front and rear?

[Sweetbriar]

Setting the alarm based on tire operating pressure is going to turn the TPMS into a 4 AM alarm clock. A 10% low limit is a good mark while a high limit of either 20% or sidewall max are good numbers. Tire manufactures have designed very robust modern tires that can take a lot of abuse and get us were we want to go but best not to push the limits to much.

[dabrooks]

My Tiffin has Michelin 255/80R22.5 tires. The Michelin tire inflation tables call for 80 lbs for the front and rear axles. I had the RV weighed and the front axle is carrying 7800 lbs and the rear 14100 lbs. That was with a full tank of gas, propane and 1/2 tank of water with the black and gray tanks empty. At 80 lbs the front axle is good for 8600 lbs and the rear is good for 15200 lbs.
To be on the safe side I carry 85 lbs all the way around. which gives me according to the inflation chart 8880 lbs front and 16160 lbs on the rear.

[AFChap]

I believe the TT is set to alarm at 15% below baseline pressure & 25% above, with baseline being whatever has been set as "cold" pressure for the weight being carried on that tire. I would NOT make the baseline pressure the max sidewall pressure as in some case even that would be grossly over inflated. Neither would I try to manipulate the high or low alarm points to a set temp as you would have to adjust it from season to season. Set the tpms to the desired baseline, and adjust the tire pressure as needed from season to season w/high & lite alarms a % of that base. I normally need to adjust my tire pressure only twice a year at most. Tire psi isn't rocket science or an exact thing. So many factors have minor effects onboth the tire psi and tire temp. It is the major changes you need to look out for. If you want all your tires to have whatever you determine to be the "ideal" pressure at any given moment in time, you will drive yourself crazy chasing a very illusive rabbit.

[hayward3411]

The TT bearing failure razed the temp to 120 degrees (other 3 tires were 75 degrees), I have not seen temps above 98 degrees during the Maryland summers. I believe setting the temps at 105 or so would have warned us but not prevent the bearing failure.

[Dennis Dean]

I have the Tireminder A1A and I cannot set my temperature setting. It is set by the software according to my manual. its like 152 degrees for alarm and 167 degrees for emergency temperature. I can set the pressure high and low to what I want. Mine are set to 90 -10 + 20, usually I see average pressure under driving conditions of 100PSI and temps from 95 to 104 Degrees. My placard shows my cold tire temp as 90PSI

[geofferyh]

Originally Posted by hayward3411

The TT bearing failure razed the temp to 120 degrees (other 3 tires were 75 degrees), I have not seen temps above 98 degrees during the Maryland summers. I believe setting the temps at 105 or so would have warned us but not prevent the bearing failure.

I think I would leave the high temperature alarm point at the recommended 158. The fact that the monitor was indicating one sensor was reading substantially higher than the other three should have been all the warning you needed to know something was going wrong.

[Alan_Hepburn]

For pressure the placard from Fleetwood says I should have 95 psi up front and 90 psi out back - that reflects both axles at the GAWR for the chassis and that is where I try to keep the pressures. On the other hand, based on the 4-corner weight results I can actually run 75 psi up front and 70 psi out back. So, I set the low pressure limit to those figures, since those are the minimum pressures required to carry the actual load - anything less and the tires are overloaded. I set the maximum pressure to 10 psi above the maximum pressure molded into the tire sidewall, since that's what the tire is rated for.

I left the temperature limit set at what TST set it at...