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Old 11-03-2019, 01:28 AM   #21
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Originally Posted by lwmcguire View Post
The real world way to tell if you are underinflated is to monitor the tire temperature. If you have tires you can't hold you hand on when driving in hot weather you are damaging your tires.

We ran trucks and trailer for over 50 years commercially and not one time did we ever let air out of tires when running back empty. Same goes for commercial rigs now. If you are going to error then error on the higher side of inflation, not the lower.
I'm not feeling good about this advice. If the tire is inflated 20% or more under the recommended inflation pressure, it could result in rapid deflation without the chance to put your hand on the tires. I suppose you could watch temps on your TPMS, but I am sure that is not what a tire designer intended. Tire temperature is important when the temperature gets high enough for reversion of the rubber, but generally irreversible radial casing fatigue has already happened by that point. That will lead to the rapid deflation I referenced. In the industry, this damage is referred to as a "zipper" failure.

I do agree with the post above about changing pressures. Loads don't generally change enough on RVs to monkey with pressures with empty/full conditions, but I don't think that was asked about here. Erring on the high side is sound advice to a point. Running 120 psi when the recommended is 82 psi is akin to running 47 psi in your car when 32 psi is recommended. Probably won't have a tire failure, but the ride quality and the wear patterns on the tires will be unacceptable.

Most everyone has given good advice on this post. Weigh the RV to get the proper inflation. The procedure for setting pressure is a bit different for a F/R weigh and a four corner weigh.

With a F/R weigh, you take the front weight and divide it by 2 to get a corner weight. Look up your pressure and then add 5 psi or 5%, whichever is greater to determine front cold tire pressures. Do the same for the rear, but remember to look on the "dual" row on the chart.

For a four corner weigh, you look at the highest of the LF and RF and set your front pressure based on that weight. You do the same for the rear.

As stated, without weighing the vehicle, inflate to the placard pressure. This pressure is generally based upon the max axle rating on the RV.

I often tell people that RV owners know more about tires than any other tire customer.
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Old 11-03-2019, 04:07 PM   #22
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I'm not feeling good about this advice. If the tire is inflated 20% or more under the recommended inflation pressure, it could result in rapid deflation without the chance to put your hand on the tires. I suppose you could watch temps on your TPMS, but I am sure that is not what a tire designer intended. Tire temperature is important when the temperature gets high enough for reversion of the rubber, but generally irreversible radial casing fatigue has already happened by that point. That will lead to the rapid deflation I referenced. In the industry, this damage is referred to as a "zipper" failure.

I do agree with the post above about changing pressures. Loads don't generally change enough on RVs to monkey with pressures with empty/full conditions, but I don't think that was asked about here. Erring on the high side is sound advice to a point. Running 120 psi when the recommended is 82 psi is akin to running 47 psi in your car when 32 psi is recommended. Probably won't have a tire failure, but the ride quality and the wear patterns on the tires will be unacceptable.

Most everyone has given good advice on this post. Weigh the RV to get the proper inflation. The procedure for setting pressure is a bit different for a F/R weigh and a four corner weigh.

With a F/R weigh, you take the front weight and divide it by 2 to get a corner weight. Look up your pressure and then add 5 psi or 5%, whichever is greater to determine front cold tire pressures. Do the same for the rear, but remember to look on the "dual" row on the chart.

For a four corner weigh, you look at the highest of the LF and RF and set your front pressure based on that weight. You do the same for the rear.

As stated, without weighing the vehicle, inflate to the placard pressure. This pressure is generally based upon the max axle rating on the RV.

I often tell people that RV owners know more about tires than any other tire customer.
I think you missed my real point and purpose of the comment regarding temperature. You need to know what the tire temperatures are whether you have a monitor or not. A simple walk around which we all should be doing each stop checking and looking is a quick way to know if you are experiencing any potential problems.

No where did I mention over inflating and simply pointing out is it better to error on having adequate psig to keep tires from heating and the tread detaching or side walls giving out.

Operating tires at sidewall psig has never caused a singe one to fail no matter if they weren't loaded up to that corresponding weight.

I think you are trying to split hairs
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Old 11-03-2019, 05:59 PM   #23
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Originally Posted by lwmcguire View Post
I think you missed my real point and purpose of the comment regarding temperature. You need to know what the tire temperatures are whether you have a monitor or not. A simple walk around which we all should be doing each stop checking and looking is a quick way to know if you are experiencing any potential problems.

No where did I mention over inflating and simply pointing out is it better to error on having adequate psig to keep tires from heating and the tread detaching or side walls giving out.

Operating tires at sidewall psig has never caused a singe one to fail no matter if they weren't loaded up to that corresponding weight.

I think you are trying to split hairs
When you stated, "The real world way to tell if you are underinflated is to monitor the tire temperature", it confused me a bit. It just seemed that you were advocating touching the tires over actually checking the pressures.
Sorry about that.

The rest of the post was meant to address the questions of the OP.

"Operating tires at sidewall psig has never caused a singe one to fail no matter if they weren't loaded up to that corresponding weight". - This is not entirely true. I have seen many impact ruptures (rabbit ears) that were at least exasperated by extreme overinflation.


On a completely different note, for the OP, here is the Michelin RV service manual. It has good information in it, though I think there may be a newer edition somewhere:

https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf
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Old 11-14-2019, 01:36 PM   #24
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Ok guys... Iím old, Polish and a retired Marine, so please use small words...
  • I havenít weighed my RV yet.
  • The sticker says 100 PSI for front and rear. We inflated them to 100 PSI in Texas when we started the trip.
  • They didnít feel hot through the trip when we touched them.
  • The next morning they were all at ~90 PSI. But it was much cooler (30-40s). My brother suggested that this was normal due to the colder ambient temps.
  • We got home (WV) without issue. Checking the feel of the tires with our hands.

Now my question. Since itís in the low 30s now, should I inflate to 100PSI before I take the RV out for a spin? If I understand the above posts correctly, the PSI will go up when the tires get warm from use. And weíre planning to drive from WV (cold!) to FL (warmer) for Christmas.
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Old 11-14-2019, 01:39 PM   #25
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Ok guys... Iím old, Polish and a retired Marine, so please use small words...
  • I havenít weighed my RV yet.
  • The sticker says 100 PSI for front and rear. We inflated them to 100 PSI in Texas when we started the trip.
  • They didnít feel hot through the trip when we touched them.
  • The next morning they were all at ~90 PSI. But it was much cooler (30-40s). My brother suggested that this was normal due to the colder ambient temps.
  • We got home (WV) without issue. Checking the feel of the tires with our hands.

Now my question. Since itís in the low 30s now, should I inflate to 100PSI before I take the RV out for a spin? If I understand the above posts correctly, the PSI will go up when the tires get warm from use. And weíre planning to drive from WV (cold!) to FL (warmer) for Christmas.
Small changes in ambient temperature result in small changes in cold tire pressure and are not enough to worry about, but I would bump those 90 PSI tires back up to 100 PSI in your new colder area.
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Old 11-14-2019, 02:48 PM   #26
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Small changes in ambient temperature result in small changes in cold tire pressure and are not enough to worry about, but I would bump those 90 PSI tires back up to 100 PSI in your new colder area.
100% right on
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Old 11-14-2019, 03:06 PM   #27
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Originally Posted by WearyTraveler View Post
Ok guys... Iím old, Polish and a retired Marine, so please use small words...
  • I havenít weighed my RV yet.
  • The sticker says 100 PSI for front and rear. We inflated them to 100 PSI in Texas when we started the trip.
  • They didnít feel hot through the trip when we touched them.
  • The next morning they were all at ~90 PSI. But it was much cooler (30-40s). My brother suggested that this was normal due to the colder ambient temps.
  • We got home (WV) without issue. Checking the feel of the tires with our hands.

Now my question. Since itís in the low 30s now, should I inflate to 100PSI before I take the RV out for a spin? If I understand the above posts correctly, the PSI will go up when the tires get warm from use. And weíre planning to drive from WV (cold!) to FL (warmer) for Christmas.
Take the coach and get it weighed. Then set your tire pressures based on the manufacturers recommendations. Arbitrarily set the pressure to max now could result in issues when you roller into higher temps with tires that have already increased by 10 percent due to rolling down the road.

If you are going to overnight between WV and FL then the morning of going to FL check the pressure and set it accordingly.
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Old 11-14-2019, 03:20 PM   #28
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https://www.jlwranglerforums.com/for...etermine.4622/


I really dislike the tire pressure conjectures.
Exact psi manufacturers recommendations are meant to protect the manufacturer, nothing else.
Tires can safely operate over a huge range of pressures and temperatures.

That whoopdie rv you see on the road? Do you really believe those four tires are within 20 pounds of one another?


Check the link above.
See if it makes sense.
Do what's shown in the link above.
You can chase Temps and pressures forever. It's a hobby for some.

A $47 tpms will make you aware and discount your worry considerably.
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Old 11-14-2019, 03:43 PM   #29
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Small changes in ambient temperature result in small changes in cold tire pressure and are not enough to worry about, but I would bump those 90 PSI tires back up to 100 PSI in your new colder area.

Correct. To reduce pressure from 100 to 90 PSI (about 10%), the temperature would have to drop in order of 50~55 F. Itís possible if starting in Texas or Florida where ambient temp could be around 90 F and then driving to cold weather area like Canada.

Iíve done that, and will add my ďpracticalĒ take on this issue. If Iím going to tour for a week or two where itís cold, and then head back to Texas or Florida, I will not adjust tire pressure due to cold weather. Mostly I leave tires alone for two reasons. First, the biggest danger of under-inflation is creating heat in tires, and since road and ambient air is colder, it self compensates.

Secondly, I always run my tires a little higher than the minimum required for the actual load; while still under the maximum tire rated pressure. I can do this because I avoid motorhomes that have chassis close to their full rated load. That way I have more tire pressure range to play with.
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Old 11-14-2019, 03:53 PM   #30
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Originally Posted by ducksface View Post
https://www.jlwranglerforums.com/for...etermine.4622/


I really dislike the tire pressure conjectures.
Exact psi manufacturers recommendations are meant to protect the manufacturer, nothing else.
Tires can safely operate over a huge range of pressures and temperatures.


Check the link above.
See if it makes sense.
Do what's shown in the link above.
You can chase Temps and pressures forever. It's a hobby for some.
I promised I was not going to reply to this thread again, yet this one sucked me back in.

I agree that that tires can operate over a relatively large range, especially over the recommended pressure for a load, but the link you provided is just not applicable in an RV/commercial application. Most RVs use steel casing radial tires. Steel cables provide greater strength and carrying capacity, yet they are more sensitive to overload/underinflation fatigue. You do not want to be setting tire pressures by putting hands on your tire or measuring footprints (unless these pressures are above the recommended). It is not that complicated.

1. If your vehicle has not been weighed:
Do not let the pressure get below the placard recommendation from your RV

2. If you vehicle has been weighed:
Run no less than the recommended pressure for the actual loads

It is as simple as that. As temps get colder, you will have to add psi to get up to one of those points described above.

Pressure will increase as you drive, no problem, the manufacturers have taken that into account.

If you want to measure footprints, put your hands on the tires, improve ride characteristics, etc.. and adjust pressures up, fine. Just make sure your pressures do not drop below either point 1 or 2 above.

I do not want to sound snarky, but this can be a serious issue. As I stated in my earlier post, if the pressure you need to carry the load is 100psi and you have 80psi or lower in that tire, it is considered "run-flat". It should be removed from the vehicle and inspected. It doesn't matter if it is a cold morning. By the time you "warm" up the tire, at 500 revs per mile, the tire will be experiencing mechanical damage.

One last note on the link that was provided concerning "chalk" pressure settings. They are doing static footprint measurements. Forces in tires change fairly dramatically as you introduce speed to equation. Centrifugal forces can be significant.
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Old 11-14-2019, 04:04 PM   #31
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I'll adjust a bit:
We can use the link as an addition to manic behavior. If you're going to be manic, do it right.
Or
Real paint, not chalk, will take centrifugals into account by allowing a real run down the road, letting you know exactly what that inside right tire likes as a pressure RANGE.

As always, I try to make my posts a hope for a seed of thought. The blossom is the readers to nourish. Extrapolation is the fertilizer.
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Old 11-14-2019, 04:17 PM   #32
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......cut.....

1. If your vehicle has not been weighed:
Do not let the pressure get below the placard recommendation from your RV

2. If you vehicle has been weighed:
Run no less than the recommended pressure for the actual loads

It is as simple as that. As temps get colder, you will have to add psi to get up to one of those points described above.

......cut.......
As you say, ďno less thanĒ, which can leave enough margin so you donít have to readjust for cold-weather deflation if you donít want to.

As an example, letís take the OP, who has tires rated at up to 120 PSI, yet the chassis only requires 82 PSI when fully loaded to maximum chassis/axle loads.

If he sets tires at ~ 90 ~ 95 PSI in warm Florida, he shouldnít have to adjust just because it gets colder (short of North Pole). Because there is a lot of difference between the required 82 PSI and the maximum 120 PSI tire rating, he doesnít have to worry as much as guys driving around in overloaded motorhomes and where tires are at maximum pressure. Those are the guys that seem to report tire failures most often.
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Old 11-14-2019, 08:37 PM   #33
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As you say, ďno less thanĒ, which can leave enough margin so you donít have to readjust for cold-weather deflation if you donít want to.

As an example, letís take the OP, who has tires rated at up to 120 PSI, yet the chassis only requires 82 PSI when fully loaded to maximum chassis/axle loads.

If he sets tires at ~ 90 ~ 95 PSI in warm Florida, he shouldnít have to adjust just because it gets colder (short of North Pole). Because there is a lot of difference between the required 82 PSI and the maximum 120 PSI tire rating, he doesnít have to worry as much as guys driving around in overloaded motorhomes and where tires are at maximum pressure. Those are the guys that seem to report tire failures most often.
Correct! The failure mode for an overinflated tire is generally not as catastrophic as an underinflated tire. You do make yourself a bit more susceptible to impact damage, but if you see that you have hit something and pull over, you will probably be ok. Yes, there is a lot more reserve capacity in 245/70R19.5 tires on an 18k chassis than on 315/80R22.5 tires on a 71k chassis.
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Old 11-14-2019, 09:59 PM   #34
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One of the worse is the Ford E-450 chassis with 5,000-pound front axle and 9,600-pound rear axle. Tires can barely reach that load at maximum inflation, so there is no room for error ó or overloading.
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Old 11-15-2019, 09:49 AM   #35
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Tire pressure

Quote:
Originally Posted by Chance View Post
One of the worse is the Ford E-450 chassis with 5,000-pound front axle and 9,600-pound rear axle. Tires can barely reach that load at maximum inflation, so there is no room for error ó or overloading.


Agreed.... had I not moved to a Super C, I would have installed a set of Commercially Rate ties like these....

https://www.goodyear.com/en-US/tires...tude-ht-c-type

They take will increase the load carrying capacity from a little over 2600 per tire for the stock tires to over 3000 per tire. They are also designed to carry heavy loads all the time unlike light truck tires.

The axles likely can more load than the door jam sticker rating but as you said the tires are the weak link.
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Old 11-15-2019, 04:40 PM   #36
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Measuring PSI while on the ground?

I'm ASSuming that when I check my pressure, the RV should be down off the leveling jacks?

The full weight of the RV should be on the tires in order to get an accurate reading, correct?
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Old 11-15-2019, 05:02 PM   #37
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I'm ASSuming that when I check my pressure, the RV should be down off the leveling jacks?

The full weight of the RV should be on the tires in order to get an accurate reading, correct?
It doesn't matter, you're overthinking it. When you purchase new tires for your car they are aired up to the correct pressure before the wheels and tires go back on the car and it is lowered to the ground.
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Old 11-15-2019, 08:59 PM   #38
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It doesn't matter, you're overthinking it. When you purchase new tires for your car they are aired up to the correct pressure before the wheels and tires go back on the car and it is lowered to the ground.
Exactly right,

The tire pressure might increase slightly if you are one of the people that run tires on the low side and like to see them squat

If like most of us do running the tires at a pressure where the load is carried without significant over flexing of the sidewall the pressure increase is negligible

The only way a tire pressure increases is to distort and reduce the volume that holds the air and this shouldn't occur in a properly load sized tire with the proper inflation
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