Tire pressure increase at summer temperatures

Our TST monitoring system recommends setting the low pressure alarm at 10% below ambient cold pressure and 20% over for the high.
i.e. Cold tire pressure 100psi low alarm 90 and high for 120
also recommend setting temp alarm for 165F

Ken

I think your alarms are a bit too tight. Drop the low to 90 and increase the high to 130. I have a light coach and recommended is 80 PSI for me tires but I've seen pressures peaks as high as a 20% increase on hot summer days. The low alarm will start driving you nuts later this year when air temps start dropping over night. Nothing like a low tire alarms at 3AM to start your day.

I don't have the monitoring, but I do check them right before leaving on trip, (get up before light and check/add as needed before leaving). I will check again depending on the trip and mileage. I don't do anything once driving or daytime hours, as the pressure I see will be different (inaccurate) than when I measured. I run at 100 psi cold.

The, what you think is, maximum pressure of tire, is not, maximum pressure cold is about 1.4 times that 120 psi = 168 psi.
I once read that they test tires to can stand an absolute ( over) pressure of 2 to 3 times the AT-pressure of yours 120 psi .
so even when warm they will blow somewhere between 240 and 360 psi.

So dont be affraid if pressure goes over 120 psi warm.
If you would fill cold at 32 degr F/0 degr C that 1.4 times 120 psi so 168 psi , and if temp in tire rises to 212degr F/ 100 degr C, the pressure would rise to 235 psi when dry air.
Can come to that at max 14,5psi by water in tire = 250 degr F.
This all ofcource will never happen for most in practice.


This must also count for the rimms, the maximum pressure they give is cold pressure, and higher pressure when warming up they can stand.

For truck tires , wich in fact your tires are, tire makers alow 20 psi over the At-pressure cold pressure.

For valves I once asked a valve importer in Holland( Europe) and there are testing standards , and what they give as maximum is cold pressure at 18 degr C/65 degr F , and rising pressure by rising temperature is standard included that they must stand.

Normal rubber snap-in valve - cold pressure maximumm 4.5/4,8bar/65/70psi( depending on brand) and mildest american standard 1,8 bar/26 psi higher when warm. DIN and ETRTO standards more extra pressure teststandard.

Metal valves can stand at least a cold pressure of 10 bar/145psi and also there pressure rising by temp rising they can stand.

mikestock wrote:
but according to my axle weights I can get by with as little as 95 psi.

If this was my situation, I would set all tire to 95#s COLD. The tire manufacturer takes into account various ambient temperatures. So no need to be concerned with ambient or tire temperatures.

-Tom

Check your rim pressure maximum as well. I am sure that mine rated at 130 could go a bit higher but I stopped the other day when one went to very close to that. I reduce the pressure just a bit because the monitor system was wining.

Even at higher ambiënt temperature, you would expect a pressure rising of 10 to 12% max and yours maximum is from 104 to 120 so about 15%, so temp in your tires gets to hot, so sertain parts of the rubber get to hot and harden,and get damaged by next bendings.

Only other way is when enaugh liqiud water in tire, wich can rise the pressure for the same higher temperature a bit more.
Will be in the range of 5 psi in practice, in theory maximum 14.5 psi when going from 32 degr F to 212 degrees F.
This water can get in by pumping the tire with a normal pump wich puts all the watergas ( humidity of ambiënt air) of the outside air in the tire. This water is in fact no problemm, cools down the tire better.

You could swich your TMPS to temperature reading, when you get the alarm, and when sensors are inside and not screwed on valves, you should have about 50degrF higher temp inside tire then ambiënt temp at your speed of 60 to 65m/h. Most likely you then still read higer difference, wich prooves the temp to be to high so the cold pressure to be to low for the load on tires.

So your pressure needs to be higher, and best is not to follow American made pressure/loadcapacity lists, but use my made lists wich give higher pressure for the same load in the lower pressures.

To check this end advice of mine, once you filled up , see if the pressure rising stays below 12% , best 10%.But if it only rises 5% its fine too.

And this will probably mean that you can use the 120 psi and still no terrible bumping and maximum reserve for more loading and unequall loading (side to side division of 47/53% is not unusual), pressure loss in time, and misreadings of pressure because of small analog schale or inacurate device.

This all will mean that you have to reset your TMPS system to a higher alarm pressure. Dont know how to, but its possible, read the manual for that, or ask the maker of it.

I have a TPMS system on my truck towing a 5th wheel.

I have found my pressures after 20 miles or so are within about 5 psi regardless of the ambient temperature during various trips.

The heat gain from the temperature rise from friction of the tire sidewalls is probably much greater than from ambient.

My cold temperature pressure is 80 psi and I see about 95psi after about 20 miles of towing where it usually stabilizes.

n0w you have more info that is confusing you.

So true.

I guess I have to agree with the 25% high but I want to know befor I get 20% low. Think I'll go with 95 psi. Having a compressor on board, I keep a close eye on the pressure and adjust before every trip. Probably didn't really need the TPMS. Just couldn't figure where else to spend that $300 and worried about a catastrophic failure on one of the dual tires and not knowing.

You might want to reset your alarm. The truck tire shop that changed my last motorhome flat said the pressure alarm high should be set for a 25% increase over cold pressures. For your 104 lbs cold, the alarm would be set at 130 lbs. (The low alarm should be set at 20% less than your cold pressure.)