Tire pressure on motorhome

[Elkhartjim]

Originally Posted by a k

Ok, how about this. My rims are only good to 130lbs. I set my tires at 120 and ten miles down the road they are reading 140. Now what? Plus the tires say do not exceed 130 lbs. what to do what to do. 'm going crazy. Does that mean I can carry a heavier load when hot?

First person I would ask this question is Newmar. What the heck are they doing using 130 lb rated wheels on a 45ft motorhome. Then I would ask you why you're running 120 lbs.

[a k]

I like to shake my wifes false teeth

[UltraKen]

Originally Posted by a k

Ok, how about this. My rims are only good to 130lbs. I set my tires at 120 and ten miles down the road they are reading 140. Now what? Plus the tires say do not exceed 130 lbs. what to do what to do. 'm going crazy. Does that mean I can carry a heavier load when hot?

The first question is why have you selected 120psi? Is this based on 4 corner weighing or something you saw on the tire wall or just a guess?

Tire pressure should be set according to the heaviest weight on each axle, by reference to the tire manuafacturer's load/pressure tables. Many add an additional 5 or 10psi to the table figure for a safety margin.

Side-wall numbers are for Minimum pressure at Maximum load. They are not the correct pressure for less than minimum load.

[bigdog]

As I have been told by several REliable sources,including my tire guy.Weigh your coach FIRST loaded for travel,then go to the tables for your tire and take that PSI number and put it in your tires.I also do what like several other people on here do and add 5# to their PSI. I don't depend on a pressure monitor as I check the tires EVERY morning when traveling for pressure and a visual on the tires.I really don't think that a pressure monitor is gonna protect you from a blow-out,etc as it's gonna happen so fast there won't be that much warning.In fact,I have seen trucks throw a gator and never lose pressure for a moment or two..

[Midniteoyl]

Have to agree with those that say to fill them up to proper pressure.. The main objective is to start the day as close to the recommended PSI as you can on a cold tire. If you start out under inflated, you are putting serious wear on the tires. This also causes excess flexing that will lead to excess heat that could lead to a blowout. Proper procedure says to fill the tire to the recommended PSI cold and let the warm temps be whatever they will be. If your heading to warmer weather, check the tires again after an overnight stop and after the tire reaches ambient temps..

Tire Tech Information - Air Pressure: When and How to Set

Drivers.com: Myths abound on correct tire inflation

Tire Inflation

[Brigadoon]

a k,

Unfortunately I cannot find it now, but someone contacted their wheel manufacturer and got the same info that the tire manufacturers advise. The psi limit on their wheels is at cold inflation. The pressure rise from there is figured into the construction of the wheel.

But don't take my word for it, just call your wheel manufacturer for the scoop.

[a k]

Thanks. Also I think most 22.5 wheels are rated for 130lbs max. The wheels are rated for 10,000lbs.

[Craig1959]

I disagree with a few things said in this thread.

1. It is perfectly safe and advisable to bleed or add air at any time when you have a good quality TPMS. The TPMS is showing actual PSI at all times. No temperature calculations or formulas are needed. You react to the number shown on the TPMS display - no rationalizations or other explanations are needed. For example: Many rims have a max PSI of 130 lbs. When your TPMS shows a higher PSI while driving, you simply stop a bleed air down to a level that more is reasonable (look below to see what that number is). Similarly, if you start a trip on a very cold morning, your TPMS will tell you that you need to add air. Don't ignore this warning. Your tires will be overloaded if you start driving with low pressure due to cold ambient air temperatures. But understand that later in the same day you may need to bleed air to maintain optimal load carrying capacity and get a softer ride as the ambient air temperature increases.

2. The root problem for many misunderstandings are the cold tire tables published by tire manufacturers. These tables assume you will only take cold tire readings prior to driving (in 2010 that's just wrong!). They factor in an arbitrary PSI increase that they know will occur when you actually start driving. For example: if the cold tire table says a particular load carrying capacity is achieved at 90 PSI cold, manufacturers are assuming the tires will actually heat up about 10% when driving. This means optimal PSI is actually about 100 PSI warm!

Most tire manufacturers are behind the times. They need to start publishing both cold and warm PSI recommendations (which they know) so that TPMS users with real-time monitoring capability can do a better job managing tire pressures.

Many people like to blame old tires and the boogy man for blowouts. After reading many RV tire pressure discussion threads I suspect many blowouts are due to improper inflation resulting from changes that occur after you start driving.

Here's how I use a TPMS to maximize tire life, safety and comfort. If you don't use a TPMS you are out of luck. This process works only when you have real-time monitoring.

1. Before each trip I let the TPMS scan all 10 tires on my coach and toad. Note: I have a TST 507 RV so monitoring can be completed before moving my coach. Many other TPMS' require you to move a few hundred feet to turn on the sensors. Not good.

I normally pick a PSI that is at the low end of the optimal manufacturer's cold range for the load limits that I have weighed previously for each axle on a commercial truck CAT scale. I know from TPMS experience that tire PSI will normally increase by 5% on rainy days, 10% on normal days and 50% on very hot days. I will adjust my cold setting up or down if I think any of these criteria will be a factor on that day.

2. While driving, I monitor tires. If they exceed the high tire or rim limits, I stop and reduce pressure by 10%. I do this because load capacity decreases along with ride comfort as pressure gets too high. Pressure has never dropped while driving so adding air has never been required. Of course, a leak or toad blowout will also be reported to me on the TPMS so I am sure will be adding air someday

I hope this helps.

[offthewall]

Originally Posted by Craig1959

I disagree with a few things said in this thread.

1. It is perfectly safe and advisable to bleed or add air at any time when you have a good quality TPMS. ...

I hope this helps.

WOW, this is one of the most ill advised bit of tire pressure information I have ever seen posted.

How do you know what the "warm" tire pressures are supposed to be? Where did you get that information? IF you knew the proper tire pressure for the load you have at every temperature and were monitoring the pressure and temperature of the tire in realtime, you could continuously adjust your pressures to match that information. Problem is two fold, you don't have that information and you would be stopping constantly, bleeding and adding air as the tire temp changed. Of course as soon as you stopped to add/delete air, the temps would change again and you'd be off when you started driving. Maybe in the future there will be such automatic systems that could do this with pressure/temp curves programmed into them for your particular tire and load. In the meantime, your method is flawed and dangerous.

The correct procedure, recommended by the tire and vehicle manufactures, is to properly inflate all tires to the recommended COLD pressure for the load you are carrying when the tires are COLD (ie at ambient temperature before driving that day). And LEAVE it that way. Very simple.

Don't ever bleed air from a warm tire to reach some empirically derived "warm" pressure reading.

[Midniteoyl]

I'd like to see where it is stated that you should bleed warm air... I have never seen this, and have always seen/been told different.

Do Not Release Hot Tire Pressure if any of these variables could be the cause of measured tire pressure exceeding the maximum psi branded on the tire's sidewall by the 2, 4 or 6 psi indicated above for the various conditions. This temporary pressure increase is expected and designed into the tire's capabilities.

http://www.tirerack.com/tires/tirete...jsp?techid=147

1. When you check the air pressure, make sure the tires are cool — meaning they are not hot from driving even a mile. (NOTE: If you have to drive a distance to get air, check and record the tire pressure first and add the appropriate air pressure when you get to the pump. It is normal for tires to heat up and the air pressure inside to go up as you drive. Never “bleed” or reduce air pressure when tires are hot.)

http://www.coopertire.com/html/produ...nce.aspx?tab=4

Tires lose air normally through the process of permeation. Changes in outdoor temperature can affect the rate at which your tires lose air. This change is more pronounced in hot weather. A tire may lose one or two pounds of air per month in cool weather and even more in warmer weather. Gradual air loss will increase the tire’s operating temperature. This can cause some of the components to separate, or damage the tire body in ways that create rapid or sudden air loss. Do not bleed air pressure when tires are hot. It is normal for pressure to build up as a result of driving.

http://ai.state.wy.us/generalservice...e%20Safet1.htm

Never bleed air from hot tires. Bleeding air from hot tires could result in under inflation.

http://www.aeolustires.com/AEOLUS-Sa...recautions.pdf

• Maintain mated duals at equal inflation pressures
• Don't bleed air from warm tires to reduce pressure buildup
• Don't inflate tires to cold PSI rating beyond rim specifications

http://www.goodyear.com/rv/tirecare/index.html

• Check inside duals as well as outside tires.
• Do NOT bleed air from hot tires.
• Inflation pressure should be adjusted to the tire carrying the heaviest load, and all tires on the axle should have the same inflation pressure.

http://www.campingworld.com/tips/rv-tire-care/45

http://www.google.com/search?ie=UTF-...ef8cda26d1a6ec

[Pairajays]

"Most tire manufacturers are behind the times. They need to start publishing both cold and warm PSI recommendations (which they know) so that TPMS users with real-time monitoring capability can do a better job managing tire pressures."

Wow, maybe someone should write all the tire manufactures and tell them they don't know what they are talking about.

Tire pressure monitor manufacturers are filling their coffers with profits with scare tactics about keeping close watch on tire pressure. A TPM is snake oil.

Jim E

[Midniteoyl]

Whats funny is that they are now mandated...

[Craig1959]

All of these warnings are outdated. They assume you are not using a TPMS.

[Craig1959]

Originally Posted by offthewall

WOW, this is one of the most ill advised bit of tire pressure information I have ever seen posted..

As someone with 12 patents to his name, I am comfortable arguing contrarian positions. But I will admit that I am disappointed when people blindly follow so called 'safety warnings' without thinking.

I have one question: How can an intelligent person say that it is dangerous to bleed air from a warm tire? Is it going to explode? Are the fumes going to kill you?

Pointing to random manufacturer's warnings does little to help. For example: My F-53 manual says you MUST check lug nut torque on all wheels every time before you drive. Clearly this warning is written by a lawyer. I will certainly question the intellect of anyone who follows this kind of warning to the letter.

Originally Posted by offthewall

How do you know what the "warm" tire pressures are supposed to be? Where did you get that information? IF you knew the proper tire pressure for the load you have at every temperature and were monitoring the pressure and temperature of the tire in realtime, you could continuously adjust your pressures to match that information. Problem is two fold, you don't have that information and you would be stopping constantly, bleeding and adding air as the tire temp changed. Of course as soon as you stopped to add/delete air, the temps would change again and you'd be off when you started driving. Maybe in the future there will be such automatic systems that could do this with pressure/temp curves programmed into them for your particular tire and load. In the meantime, your method is flawed and dangerous.

You speak like someone without a TPMS. You should get one. Within a few days of driving you will be able to record the information that manufacturers will not normally provide. You will quickly learn what the normal warm temperature relative to the published cold temperature.

Think! Why do manufacturers tell you to NOT bleed warm air? They're afraid that you will bleed down to the published cold temperature and then end up under-inflated when your tires eventually cool down.

When I bleed warm air, I bleed down to the normal warm temperature that I have observed hundreds of times in the past.

Originally Posted by offthewall

The correct procedure, recommended by the tire and vehicle manufactures, is to properly inflate all tires to the recommended COLD pressure for the load you are carrying when the tires are COLD (ie at ambient temperature before driving that day). And LEAVE it that way. Very simple.

Don't ever bleed air from a warm tire to reach some empirically derived "warm" pressure reading.

Ambient temperature is irrelevant to someone using a TPMS. You simply react to the PSI shown on the TPMS screen. If you haven't started driving, you match the published cold temperature, regardless of ambient outside temperature[. Ambient temperature is the cause for changes in pressure. The TPMS simply reflects the result of temperature changes. That's what you need to care about.

Once you start driving, you then use you TPMS to match the normal observed warm temperature. Simple, accurate and much safer that relying on old-fashioned cold temperature readings.

Someday, manufacturers will publish warm tire data. For now, only TPMS owners will have the ability to drive with this extra level of safety.