Tire Pressure

[smoothie]

So I purchased a TPMS for the Landmark. The trailer came with Sailun (hopefully I spelled that correctly) tires with a cold pressure spec of 125 psi. I took the Landmark to the shop for some work and tested out the TPMS. The front tires went from 125 psi to 138 psi and temp of 48 degrees. The rear set went from 125 to 142 psi at 51 degrees. Is this a normal increase in pressure? Also will there normally be a difference in pressures from front and rear? Oh yeah the trailer is empty. Any assistance is greatly appreciated?

 

[RickL]

So I purchased a TPMS for the Landmark. The trailer came with Sailun (hopefully I spelled that correctly) tires with a cold pressure spec of 125 psi. I took the Landmark to the shop for some work and tested out the TPMS. The front tires went from 125 psi to 138 psi and temp of 48 degrees. The rear set went from 125 to 142 psi at 51 degrees. Is this a normal increase in pressure? Also will there normally be a difference in pressures from front and rear? Oh yeah the trailer is empty. Any assistance is greatly appreciated?

Lets start first with cold inflation - hopefully you know the exact weights of each wheel position, if not each position at least the weight of each axle position. Once you determine those (keep in mind that these weights are as you would normally be packed at including any water you may carry) then you can set the tires to the proper pressure. Just because the sidewall states 125 PSI, you may only require say 90 PSI to safely carry your weight. Over inflation can create irregular wear issues. There are a number of sights that can provide you with PSI and weights for your particular tire size. ALWAYS SET ALL OF THE TIRES TO THE HIGHEST PSI THAT MATCHES THE HEAVIEST WHEEL/AXLE POSITION.

Next, as for the changes in tire pressure - yes the tires will increase in PSI depending on a number of factors, load, speed, and inflation to name a few. Ambient temp can and will also pay a role in any increase (along with variance in altitude). Keep one thing in mind, cold inflation is the inside of the tire matching the exterior in terms of temperature. As you check “hot” inflation NEVER deflate the tire if it appears to be higher then the recommended pressure.

If if you set your pressure and you see variations with the TPMS I would double check with an air gauge to verify that there are truly differences between the wheel positions. There is a possibility that the TPMS could be off.

Finally, your temp difference (assuming everything started out correct) could indicate more weight on the rear axle then the front axle. Keep in mind I’m only going off your info.

 

[JohnDar]

Lets start first with cold inflation - hopefully you know the exact weights of each wheel position, if not each position at least the weight of each axle position. Once you determine those (keep in mind that these weights are as you would normally be packed at including any water you may carry) then you can set the tires to the proper pressure. Just because the sidewall states 125 PSI, you may only require say 90 PSI to safely carry your weight. Over inflation can create irregular wear issues. There are a number of sights that can provide you with PSI and weights for your particular tire size. ALWAYS SET ALL OF THE TIRES TO THE HIGHEST PSI THAT MATCHES THE HEAVIEST WHEEL/AXLE POSITION.

Next, as for the changes in tire pressure - yes the tires will increase in PSI depending on a number of factors, load, speed, and inflation to name a few. Ambient temp can and will also pay a role in any increase (along with variance in altitude). Keep one thing in mind, cold inflation is the inside of the tire matching the exterior in terms of temperature. As you check “hot” inflation NEVER deflate the tire if it appears to be higher then the recommended pressure.

If if you set your pressure and you see variations with the TPMS I would double check with an air gauge to verify that there are truly differences between the wheel positions. There is a possibility that the TPMS could be off.

Finally, your temp difference (assuming everything started out correct) could indicate more weight on the rear axle then the front axle. Keep in mind I’m only going off your info.

The rolling pressure will differ between all four tires due to the weight distribution of the trailer. It is not equal at each point. The side in the sun as you roll will also be higher than the shaded side.


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[RickL]

The rolling pressure will differ between all four tires due to the weight distribution of the trailer. It is not equal at each point. The side in the sun as you roll will also be higher than the shaded side.


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Having been in the tire industry for over 35 years I’m a little confounded on your term “rolling pressure” in the way you explain it. Could you please clarify what it is and why it is different then static pressure.

I wil agree that a “sun” side tire MAY experience a slight pressure differential over the “shade” side. How much is open to discussion as I believe it may only be 1 PSI. There is a 1 PSI inc/dec for every 10 degrees in temp.

 

[JohnDar]

Having been in the tire industry for over 35 years I’m a little confounded on your term “rolling pressure” in the way you explain it. Could you please clarify what it is and why it is different then static pressure.

I wil agree that a “sun” side tire MAY experience a slight pressure differential over the “shade” side. How much is open to discussion as I believe it may only be 1 PSI. There is a 1 PSI inc/dec for every 10 degrees in temp.

Rolling down the road. Temps and pressure will vary from side to side and between each tire depending on what the load is above it. I’ve had my rig professionally weighed and each tire had a different load over it.


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[TedS]

I've seen statements that tire pressure will change 1% and 2% for every 10°F change. So that would be 1 to 2 psi for a tire at 100psi.

The 13psi change would mean the tire temp changed about 60°F. Did it? Or about 130°F. Did it?

 

[RickL]

Rolling down the road. Temps and pressure will vary from side to side and between each tire depending on what the load is above it. I’ve had my rig professionally weighed and each tire had a different load over it.


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Rolling down the road can mean 30 mph or 70 mph. I would submit that at 30 mph you would see little pressure differential between tires (there are variables but in terms of talking rv’s it’s a non issue, in terms of container haulers 1 1/2 mph compared to 2 or 2 1/2 is a major impact fully loaded).

The increase you are seeing while “rolling” comes from weight and speed. So it stands to reason the heavier and faster one goes the pressure will increase as the tire temps increase with these two variables. Still has little to do with cold inflation which must be set prior to the unit moving.

 

[JohnDar]

Rolling down the road can mean 30 mph or 70 mph. I would submit that at 30 mph you would see little pressure differential between tires (there are variables but in terms of talking rv’s it’s a non issue, in terms of container haulers 1 1/2 mph compared to 2 or 2 1/2 is a major impact fully loaded).

The increase you are seeing while “rolling” comes from weight and speed. So it stands to reason the heavier and faster one goes the pressure will increase as the tire temps increase with these two variables. Still has little to do with cold inflation which must be set prior to the unit moving.

Typical speed is 65 mph pulling the trailer. And I have TPMS on it.


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[smoothie]

Just so I am clear. I have heard that you should fill tires to cold pressure because that is the pressure required to carry maximum load. Would that cause an issue if I am not fully loaded? My other issue was the TPMS has I believe a 15% over and under on PSI from the initial preset which I put in as 125. The TPMS warning alarm went off when the rear set hit 141 psi. Should I extend the over/under range so the alarm goes off later? Trying to avoid going into panic mode if not necessary.

 

[mlpeloquin]

You need to weigh the fifth wheel fully loaded for a trip. Then using a Load/Pressure Chart for the tire size and weight rating yours have set the tire pressure for 5 to 10 psi above the recommended pressure on the chart. That way you are not constantly adjusting the tire pressure do to mid day vs early morning temps. Over inflating a tire with a much lighter load will cause a hard ride and bouncing inside the fifth wheel. You should not need 125psi, but without weighing you cannot know what pressure is correct.

I need 95psi for the weight I carry fully loaded by the Load/Pressure Chart. I set mine at 105psi. While driving the pressure goes up as high as 128psi in the desert in the heat of the summer. Otherwise I see the pressure around 118psi. The temperature have never gotten over 136 degrees.

 

[smoothie]

Thank you to everyone for the great information. Now I just need to find a weigh station near me.

 

[RickL]

You need to weigh the fifth wheel fully loaded for a trip. Then using a Load/Pressure Chart for the tire size and weight rating yours have set the tire pressure for 5 to 10 psi above the recommended pressure on the chart. That way you are not constantly adjusting the tire pressure do to mid day vs early morning temps. Over inflating a tire with a much lighter load will cause a hard ride and bouncing inside the fifth wheel. You should not need 125psi, but without weighing you cannot know what pressure is correct.

I need 95psi for the weight I carry fully loaded by the Load/Pressure Chart. I set mine at 105psi. While driving the pressure goes up as high as 128psi in the desert in the heat of the summer. Otherwise I see the pressure around 118psi. The temperature have never gotten over 136 degrees.

Just to be clear, it is NOT necessary to over inflate the tires over your max load. Checking and adjusting the air pressure when the tire is at ambient temperature covers you regardless of the temp increase or amount of travel. The load and weight chart takes all that into effect.

 

[busted2341]

Having been in the tire industry for over 35 years I’m a little confounded on your term “rolling pressure” in the way you explain it. Could you please clarify what it is and why it is different then static pressure.

I wil agree that a “sun” side tire MAY experience a slight pressure differential over the “shade” side. How much is open to discussion as I believe it may only be 1 PSI. There is a 1 PSI inc/dec for every 10 degrees in temp.

RickL

In almost 3 years of traveling over 18K miles on my Landmark, I have found that shade tires run almost 5 to 8 lbs less then sun side tires. I also discovered that when stuck in traffic doing say 30 mph both temps and pressure increase until highway speed is reached which then lowers both temp and pressure. I run 110 lbs (125 max by sidewall)in my tires. Maximum pressure driving through AZ in June was 136 lbs. I don't recall the temp but I believe it was close to the pressure. I have my TPMS set at 90 low and 156 high with the temp alarm at just below blow temp of 180 I believe......What do you think? Should I change anything? Looking for that experience.

 

[RickL]

RickL

In almost 3 years of traveling over 18K miles on my Landmark, I have found that shade tires run almost 5 to 8 lbs less then sun side tires. I also discovered that when stuck in traffic doing say 30 mph both temps and pressure increase until highway speed is reached which then lowers both temp and pressure. I run 110 lbs (125 max by sidewall)in my tires. Maximum pressure driving through AZ in June was 136 lbs. I don't recall the temp but I believe it was close to the pressure. I have my TPMS set at 90 low and 156 high with the temp alarm at just below blow temp of 180 I believe......What do you think? Should I change anything? Looking for that experience.

Im assuming all of your readings are being captured off your TPMS. While I’m not saying the readings are incorrect it would be interesting to verify them off a calibrated analog gauge. My biggest reason to question the readings are pressures and temps higher at lower speeds. Almost any tire shop should have a master gauge to check yours. If they don’t I’d run fast. It’s not uncommon to find tire shops that fail to check thier gauges. When I managed shops, either one or multiple I made it mandatory to check gauges once a week.

As to your pressures being being correct it would be important to know the weights per wheel (the best method) or by axle. I’m assuming you have 215/75R17.5 LR H.

Lastly, not too sure were the temp of 180 degrees equals blow out. Most new tires are cured in the 340-360 degree area (give or take). So the typical failure where the tread or carcass comes apart is when it reaches the cure temps. I wouldn’t recommend running much over 200 degrees ( as any sudden increase would come very quick, which when you lose air pressure occurs faster then you can normally stop) but 180 degrees is a safe temp. If you start to approach that temp I would slow down as the jouncing of the sidewall will only add to the temp. Think in terms of taking a coat hanger and bending it and rapidly bend it back and forth. That is what a steel body carcass is like.

 

[avvidclif]

Higher temp at slower speeds is easy. Middle of July, outside temp over 100. Asphalt over 140. Not near as much air to cool the tires at slower speeds.