TPMS with large temperature swings

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blw2

blw2

Well-known member
Joined
Aug 9, 2012
Posts
3,364
Location
Saint Johns, FL
On my recent trip out west, I started having pressure problems along about New Mexico.  Charles' Law and Boyle's Law in action!

My tires would be low in the cooler mornings there in the desert, but then I would get over pressure alarms as it warmed up.

I'll bet folks that live out in the desert have a lot of tire problems!

Where do you set your tires to avoid this issue?

 
I've learned to accept low pressures in the morning, as long as they're even on axles. Within 5 min of low speed driving they've all returned to normal. Not in AZ at the moment (thank goodness!) so haven't run in to over pressure issues yet this year. Eezrv lets you set the pressure warnings so that helps.
 
My Pressure Pro TPMS sensors take their base pressure at the time they are screwed onto the valve stem.  So when I have screwed them on when the temp was around 80 degrees, and I plug in the monitor in a cold morning some days later the low pressure alarm goes off.  Just a fact of life about the way the senors work.  What IS aggravating is when I forget to power off the monitor and the alarm goes off at 3am.  Gur :mad:rr.
 
Sun2Retire said:
I've learned to accept low pressures in the morning, as long as they're even on axles. Within 5 min of low speed driving they've all returned to normal. ......
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that's exactly what I found....but it's killing me.  I have been obsessive about tires....especially since the blowout.  And it kills me that i have now run these new tires "under pressure"  for the load now a few times.  I know it's only a few minutes..... & I have been keeping the speed down while they warm up...but still.  Oh well, i guess it can't be any worse than the damage all these horrible roads have caused!
 
lynnmor said:
Adjust your over pressure setting a bit higher.
Click to expand...

Yeah, I considered doing that.... but not knowing the science or logic around these setpoints..... I just don't know what it's based on...what sorts of safety factors are involved, etc....
 
As mentioned the most important thing is that the tire pressures are the same on any given axle while under way or when there is no sun hitting the tires when not under way.

I check my pressures in the morning before the sun has hit any of the tires.

I have also found after 20 miles of travel the pressures are very close to each other if they were when I checked them that morning.

I have also found while under way even the tires in the sun usually run less than 3 psi different from the ones on the shade side of the trailer.  This is with E rated tires at 80 psi cold.  I set my upper pressure at 95 psi when cold setting is 80 psi.
 
#1. Set the cold tire pressure in the morning when its cool and make sure it is adequate pressure for the load. Maybe not much extra margin, but at least adequate.

#2. Make sure the TPMS is calibrated to those same cold morning psi values.

#3. Set the TPMS high pressure alarm high enough to avoid false alarms. There is no science to the high value because no tire manufacturer specifies a high max psi or temperature while driving. Obviously a tire could burst at some point, but it's well out of bounds for US driving conditions. You just need to trust the tire engineers on that.  The supposed purpose of the high temp alarm is to spot a wheel that is overheating due to a bad bearing, stuck brake pad, etc.  That wheel will [eventually] get hot enough to alarm, so no need to make the trigger point really low. You are only looking for a tire that is running substantially hotter than the others.
 
blw2 said:
Yeah, I considered doing that.... but not knowing the science or logic around these setpoints..... I just don't know what it's based on...what sorts of safety factors are involved, etc....
Click to expand...

blw2
IMO very few people understand the meaning of, (or the use for the "temperature readings" and/or the "temperature alarms" that TPMS provide.
As always information, (no mater how accurate)... is of NO value if you don't know what it means.
 
And with the TPMS sensors at the end of the valve stems, the high temp readings are even less accurate. I raised my high temp threshold up 15 degrees on the monitor.  I am much more likely to notice a high temp reading than the system alarm as I (like you) randomly monitor the readouts.
 
I have found the temperature readings from the external mounted TPMS sensors basically give you the ambient temperature.  The sensors in the sun will give a higher reading even though the pressure has not increased.

I have had pressures on the sunny side of my trailer only 1-2 psi higher than the ones on the shade side while under way.  But the temperatures on the sunny side may be 10-20 degrees higher.

As far as I am concerned the temperature reading of no use while under way.
 
Not necessarily. I have saw elevated temps on a wheel when the tire was losing air and causing the tire to heat up. It does work,  it is just not real specific. 
 
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