Tire pressure

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pipepro

pipepro

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Joined
Jan 2, 2012
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Northeast Ohio
I have bf goodrich tires and on the label inside my rv the cold pressure says 92 psi but on my tires it says 110 under max load. I split the difference and put 100 in them. Did I do right?
 
pipepro said:
rv the cold pressure says 92 psi but on my tires it says 110 under max load.
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I guess the question is, are they at max load? I would think the door sticker was best, but slightly higher is better than slightly lower. It might affect your drifting with slightly higher tires, probably not significant to worry.
 
We are on a weekend trip and while driving on the interstate on our way they were at 110psi they were very loud. I went to tractor supply and bought a tire gauge. That is when I let some air out of them.
 
pipepro said:
We are on a weekend trip and while driving on the interstate on our way they were at 110psi they were very loud. I went to tractor supply and bought a tire gauge. That is when I let some air out of them.
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Not a good thing to do when the tires are hot. Tires always gain preasure as they warm up. You need to check them COLD. In plane language in the morning before moving the coach. Personally I would inflate them per the body mfg lable
 
I did check them cold. We have been camped since yesterday. I'm questioning the tire gauge I bought also. I will check them with another gauge when we get home.
 
The steer tires on our coach are set at 110 psi, exactly what the load chart says for the weight they carry. On the highway at 65-70 mph in ambient temps of 85 to 90 degrees F, the pressure will rise to 126. Totally normal.

You should never let air out of a hot tire.
 
pipepro said:
I have bf goodrich tires and on the label inside my rv the cold pressure says 92 psi but on my tires it says 110 under max load. I split the difference and put 100 in them. Did I do right?
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What you did is excessive but probably not harmful. The label inside the RV is the manufacturers recommendation for the Rv when at its max design weight (GVWR). If you don't overload the RV, there is never any need to exceed the 92 psi label. Your tires are capable of carrying more weight (the amount shown on the sidewall), but you should not be doing that, so neither the 100 nor the 110 is necessary or desirable.
 
I suggest you search this topic here. There are several good articles and threads available with top notch advice! Most start with "... weigh your coach (by axle and position) to determine tire pressures". These folks have been quite helpful!
 
^^ What Rusty said. You'll know exactly the PSI level needed by weighing your coach, when it's fully loaded for travel. Take the axle weight, divide by 2 for the front (since there are 2 tires) and divide by 4 for the rear (since there are 4 tires) and adjust your PSI accordingly based on the tire manufacturer's inflation charts. RV weighing can be done at truck stop CAT scales, or gravel yards or grain elevators that have public-use truck scales available.

As you discovered, running motorhome tires at max PSI will cause an unnecessarily rough ride unless the rig is actually carrying its max weight (which is rare). Trailer tires, on the other hand, should be inflated to max PSI for the most part.
 
scottydl said:
^^ What Rusty said. You'll know exactly the PSI level needed by weighing your coach, when it's fully loaded for travel. Take the axle weight, divide by 2 for the front (since there are 2 tires) and divide by 4 for the rear (since there are 4 tires) and adjust your PSI accordingly based on the tire manufacturer's inflation charts. RV weighing can be done at truck stop CAT scales, or gravel yards or grain elevators that have public-use truck scales available.

As you discovered, running motorhome tires at max PSI will cause an unnecessarily rough ride unless the rig is actually carrying its max weight (which is rare). Trailer tires, on the other hand, should be inflated to max PSI for the most part.
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Assuming both axle ends are exactly the same weight can result in tire failure. A retired tire construction engineer recommends using a minimum of 52% of actual axle weight when calculating tire pressure to allow for loading differences.
I always go by the recommended pressures on the Federal Tire Placard in every vehicle so I never have to be concerned if tire pressures are adequate.
 
While on this topic, I have a question about pressure increase while traveling.

I know they will heat up and the pressure will go up.

Given a cold pressure on my trailer tires of 80, what would be reasonable to see down the road a bit. I now have my TPMS set up so can watch it instead of the road 😀
 
It varies quite a bit with speed, road surface, ambient temperature, etc. , but 8-10 psi would be common for that size tire and 15 not unheard of. 10%-20% increase.
 
A Traveler said:
The steer tires on our coach are set at 110 psi, exactly what the load chart says for the weight they carry. On the highway at 65-70 mph in ambient temps of 85 to 90 degrees F, the pressure will rise to 126. Totally normal.

You should never let air out of a hot tire.
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Why not?
 
Babe2201 said:
Why not?
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Tire mfgrs. have taken this normal occurance into consideration when designing tires. Owner/operators need not be concerned with anything but COLD tire pressures. This is the subject of Boyle's Ideal Gas Law and cannot be defeated.
What causes higher pressures than normal is the presence of moisture/water, as it turns into higher humidity water can expand by near 1,700%.
This explains fully: Air- Moisture Holding Capacity vs. Temperature
The natural conclusion is to use a water/moisture trap on your air compressor when adding air to tires.
 
Last edited:
Babe2201 said:
Why not?
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Because that’s not how it works, and it is not what the manufacturers intended when they designed the tire. It is not a proper procedure.

if you let air out of a hot tire, what happened when it cools down? Now it is severely UNDER-inflated. So do I put air back in it now? No…again, that’s not how it works.

The manufacturers know that the pressure will rise when the tire gets hotter. That tends to “stiffen” the tire. However, the sidewalls get a bit ”softer” when the tire gets hot. The two conditions tend to cancel each other out, and the tire runs just fine with increased pressure at higher temps.
 
A Traveler said:
Because that’s not how it works, and it is not what the manufacturers intended when they designed the tire. It is not a proper procedure.

if you let air out of a hot tire, what happened when it cools down? Now it is severely UNDER-inflated. So do I put air back in it now? No…again, that’s not how it works.

The manufacturers know that the pressure will rise when the tire gets hotter. That tends to “stiffen” the tire. However, the sidewalls get a bit ”softer” when the tire gets hot. The two conditions tend to cancel each other out, and the tire runs just fine with increased pressure at higher temps.
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So if you are talking about setting air pressure it is one thing but you said to NEVER let air out of a hot tire. Quite often I have customers that have put way too much pressure in their tires and when I check them I have to take some out and when we have to let air out of them to change them as well.

FWIW you can check and set them when they are warm as well. It is best to do them when they are cold but can be done by adding a little bit for them being warm. It would be a good idea to check them and adjust them at a later time when they are cool but not everybody has a compressor at their house.
 
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