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Question Why do RV tires gain so much pressure?

 

 Bill Schmidt
(@Bill Schmidt)
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Joined: 3 weeks ago
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I've often wondered why the tires on my travel trailer will gain about 10-12psi on a trip, and the tires on my tow truck only gain about 4-5 psi.  The tires on my trailer are Goodyear Endurance load range E, with a cold pressure rating of 80psi.  (The original Chinese tire bombs were load range D with a cold pressure rating of 65psi.  I had the same problem with them gaining pressure).  I usually start my trips with the pressure set at 75psi instead of 80psi because I'm nervous about the tires gaining so much pressure.  On a typical travel day in the summer (in Texas) the tires wil usually go from 75 to about 87 or 88psi crusing down the highway at 65MPH.  I have a TST pressure monitoring system, and I have a lot of faith in it.  My trailer weighs 9950lbs according th the CAT scale.


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 Roger Marble
(@Roger Marble)
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Joined: 6 months ago
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Tire pressure will increase i.e. gain about 2% for each increase in temperature of 10F. I have covered this in detail in a few posts on my blog. Here is one post on that topic.

https://www.rvtiresafety.net/2016/01/does-tire-pressure-really-follow-gas-law.html

Since your TT tires carry a much higher load relative to their size they have to work harder than your truck tires. Inflation on trucks gives tires a 10% to 30% Reserve load while the inflation specified for TT tries may give 0% Reserve.

 

What can confuse the issue is when you change the Load Range and can run a different pressure  BUT a couple observations. When you increase the tire Load Range you only get an increase in load Capacity when you also run higher inflation.

Without knowing the scale reading for each axle and the actual tire sizes I can only give you generalizations. It is very unlikely that your 9950# is evenly split across all 4 tires and probably one or more is supporting more than 2,487#.

You should NOT get nervous about pressure gain as we tire engineers know the temperature will increase and also the pressure will increase.  You can email me directly at tireman9@gmail.com and I will be happy to work directly with you to resolve your questions and concerns.

Some information that will help us.

1. Complete tire size and Load Range info for both TT and TV

2. Scale readings for all 4 axles (TV & TT)

3. Cold inflation for the TV.  You said 75 for the 4 TT tires


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 Bill Schmidt
(@Bill Schmidt)
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Joined: 3 weeks ago
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Roger,

Thank you for your response.  It makes me feel much better now.

I was reading today's issue of the RV Travel Newsletter, and saw my question in your "RV Tire Safety" article.  I feel honored!

I'm sorry I haven't responded before now, but I've been out of town on a business trip for the last couple of weeks.  I'll be back at home next week and will provide the answers to your questions.  I no longer have the scale information you asked for, but I can provide the other information.

Bill


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 David Christiansen
(@David Christiansen)
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Joined: 1 week ago
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I am a retired mechanical engineer, though not a Tire Engineer.  Understand the basic relationship between temperature and pressure of an ideal gas.  I admit, I don't worry too much about the pressure/temperature because I invested in a TPS system and ensure that we start our day's travels with the tires all at their cold pressure.  I rely on the system alarms to alert me of a problem (high temperature at 154F, 20% over cold pressure for a high pressure alarm and 5 psi below the cold pressure for low pressure alarm).

 

I would like to hear if I am putting too much faith in the TSP system?

 

Thanks Dave


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 Roger Marble
(@Roger Marble)
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Joined: 6 months ago
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You are OK in depending on your TPMS.   I do suggest that people do a once-a-year test by partially unscrewing the sensor from each wheel and confirming the monitor provides a warning at the expected "low inflation" point.

Don't forget to re-inflate the tires after you do the test.


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 David Christiansen
(@David Christiansen)
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Joined: 1 week ago
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Thanks for the advice - didn't think of verifying the low pressure alarm.   Though,  after we soever the winter in Pigeon Forge and was preparing to get back on the road,  found that I needed to add air to most of the tires,  because of the alarm turning on the TPMS.

Feels like the rest was performed,  just out of dumb luck.


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