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tire pressure

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ridingarocky
Reg. Aug 2008
Posted 2009-04-22 11:58 PM (#103788)
Subject: tire pressure



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I have what is probably a stupid question for ya'll but I wouldn't ask if I already knew the answer... If your trailer tire states that it takes 65lbs pressure cold, does that mean during cold weather or does that mean before hitting the road and warming up.. i filled my tires today to 50 lbs and it states 65lbs cold.. it's now warm, almost summer weather already.. I'm hauling 2 horses weighing @ 1000lbs each.  Should I go fill my tires some more tomorrow before setting out?
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hosspuller
Reg. Oct 2003
Posted 2009-04-23 1:07 AM (#103789 - in reply to #103788)
Subject: RE: tire pressure


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Cold pressure means before hauling the trailer any significant distance.  But unless you have a compressor at home, you 'll just have to fill the tires at the service station.  

Since trailer tires don't have to steer or drive... Just inflate them to the max pressure as marked on the tire sidewall. You'll want to check them before any long trip.  Tires will slowly lose pressure over time.

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PaulChristenson
Reg. Jan 2007
Posted 2009-04-23 1:36 AM (#103792 - in reply to #103788)
Subject: Latent Heat of Evaporation


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Originally written by ridingarocky on 2009-04-22 12:58 AM

I have what is probably a stupid question for ya'll but I wouldn't ask if I already knew the answer... If your trailer tire states that it takes 65lbs pressure cold, does that mean during cold weather or does that mean before hitting the road and warming up.. i filled my tires today to 50 lbs and it states 65lbs cold.. it's now warm, almost summer weather already.. I'm hauling 2 horses weighing @ 1000lbs each.  Should I go fill my tires some more tomorrow before setting out?
The cold pressure is a maximum, because air contains water vapor. That water vapor will condense into water at the dew point of the air. The dew point depends on pressure and temperature. If you increase the pressure, you increase the dew point temperature where the vapor becomes water. Conversely, if you reduce temperature at a given pressure, you reduce the dew point.The moisture moving from a liquid to gaseous state as the tire heats and cools that creates the greatest expansion inside the tire.The law that you are using applies only to a materials that are fully saturated with the Latent Heat of Evaporation and have completely become a gas.[Think on what happens at the boundary of cold aluminum Coke can retrieved from the cooler on a warm humid day. Condensation forms on the can because the cold can cools the air at the boundary of the can, exceeding the dew point of the water vapor in the air. It's also what happens when warm air meets cold air, which is where we get weather fronts, clouds and rain]Back to tires and compressed air. The air in the compressor will have a higher dew point than air at atmospheric pressure. This is why a basic air compressor hose is sometimes wet. Its the condensation of water vapor as it moves from the compressed state (high dew point) to the lower pressure (lower due point). If you use the compressor to fill a tire with air, and since the compressed air will be of higher pressure than the final air pressure in the tire (if not, then the compressor would not be able to pressurize the tire), the dew point of the air in the tire will be less than the air from the air compressor; you will likely have water in the tire.As the tire heats up, the water will vaporize, which results in a more significant pressure increase than the gas law. As the tire cools, the reverse occurs.
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Tresvolte
Reg. Feb 2008
Posted 2009-04-23 8:45 AM (#103802 - in reply to #103792)
Subject: RE: Latent Heat of Evaporation




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Originally written by PaulChristenson on 2009-04-23 1:36 AM

Originally written by ridingarocky on 2009-04-22 12:58 AM

I have what is probably a stupid question for ya'll but I wouldn't ask if I already knew the answer... If your trailer tire states that it takes 65lbs pressure cold, does that mean during cold weather or does that mean before hitting the road and warming up.. i filled my tires today to 50 lbs and it states 65lbs cold.. it's now warm, almost summer weather already.. I'm hauling 2 horses weighing @ 1000lbs each.  Should I go fill my tires some more tomorrow before setting out?
The cold pressure is a maximum, because air contains water vapor. That water vapor will condense into water at the dew point of the air. The dew point depends on pressure and temperature. If you increase the pressure, you increase the dew point temperature where the vapor becomes water. Conversely, if you reduce temperature at a given pressure, you reduce the dew point.The moisture moving from a liquid to gaseous state as the tire heats and cools that creates the greatest expansion inside the tire.The law that you are using applies only to a materials that are fully saturated with the Latent Heat of Evaporation and have completely become a gas.[Think on what happens at the boundary of cold aluminum Coke can retrieved from the cooler on a warm humid day. Condensation forms on the can because the cold can cools the air at the boundary of the can, exceeding the dew point of the water vapor in the air. It's also what happens when warm air meets cold air, which is where we get weather fronts, clouds and rain]Back to tires and compressed air. The air in the compressor will have a higher dew point than air at atmospheric pressure. This is why a basic air compressor hose is sometimes wet. Its the condensation of water vapor as it moves from the compressed state (high dew point) to the lower pressure (lower due point). If you use the compressor to fill a tire with air, and since the compressed air will be of higher pressure than the final air pressure in the tire (if not, then the compressor would not be able to pressurize the tire), the dew point of the air in the tire will be less than the air from the air compressor; you will likely have water in the tire.As the tire heats up, the water will vaporize, which results in a more significant pressure increase than the gas law. As the tire cools, the reverse occurs.

I read this all the way through three times...are you recommending not to use the maximum cold pressure, or to use the maximum cold pressure?

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gard
Reg. Aug 2007
Posted 2009-04-23 9:02 AM (#103803 - in reply to #103788)
Subject: RE: tire pressure


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The tire should be filled to its maximum cold pressure as indicated on the sidewall. As it is being used, the air will warm, expand, and increase the internal pressure beyond its initial pressure. This variance is built into the operating pressures allowed by the manufacturer.

If the tire is being used, and the pressure is checked and found to be high, some people will let the excess air out. This will result in an under inflated tire, and should not be accomplished.

That is why tire pressures should be checked when cold.

Gard

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Tresvolte
Reg. Feb 2008
Posted 2009-04-23 9:49 AM (#103807 - in reply to #103803)
Subject: RE: tire pressure




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I agree with you Gard...I was just trying to figure out exactly what Paul was telling us.

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BlazingCreekBar
Reg. Nov 2008
Posted 2009-04-23 5:00 PM (#103847 - in reply to #103788)
Subject: RE: tire pressure


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According to the manufactures guidelines inflate the vehicles tires to the pressure ratings on the door tag. My F350 Dually calls for 75 psi front and 60 psi rear. Yet the tires are rated for 80 psi max. Based on the postings above should I disregard the vehicle manufactures ratings and inflate to Max pressure? The tag on my trailer lists the 80 psi max per axel. Yet if you search on the internet it is recommended not to pressure to the max PSI ratings as these are considered Maximums.I am unsure what a trailer tire should be now and I definitely do not believe it should be brought to or above maximum ratings.
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retento
Reg. Aug 2004
Posted 2009-04-23 6:24 PM (#103853 - in reply to #103788)
Subject: RE: tire pressure


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If you don't want to run the maximum pressure.... Weigh the trailer loaded and inflate the tires accordingly...

 

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hosspuller
Reg. Oct 2003
Posted 2009-04-23 6:30 PM (#103854 - in reply to #103847)
Subject: RE: tire pressure


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Originally written by BlazingCreekBar on 2009-04-23 2:00 PM

According to the manufactures guidelines inflate the vehicles tires to the pressure ratings on the door tag. My F350 Dually calls for 75 psi front and 60 psi rear. Yet the tires are rated for 80 psi max. Based on the postings above should I disregard the vehicle manufactures ratings and inflate to Max pressure? The tag on my trailer lists the 80 psi max per axel. Yet if you search on the internet it is recommended not to pressure to the max PSI ratings as these are considered Maximums.I am unsure what a trailer tire should be now and I definitely do not believe it should be brought to or above maximum ratings.

The original poster was speaking about trailer tires.  You seem to be speaking about truck or vehicle tires.  These are separate issues.  Your TRUCK tires have to steer or drive.  The truck manufacturer's tire pressures are figured for traction, ride, load and wear.  Follow their recommendations.

Trailer tires are just along for the ride.  Air them to max cold pressure as stamped on the tire sidewall.

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gard
Reg. Aug 2007
Posted 2009-04-23 10:49 PM (#103859 - in reply to #103788)
Subject: RE: tire pressure


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There are two factions within this forum; those who run their truck tires at the maximum pressure as indicated by the tire manufacturers, and those who follow the recommendations of the truck manufacturer.

I choose the tire manufacturer's recommendations. I can do so, because I don't normally use my truck in an unloaded configuration, which would usually cause the center threads of the tires to wear more quickly. I enjoy even tire wear patterns, and I don't have to re-air when I'm ready to pull.

On my truck and trailers, I always run at the maximum rated tire pressures. This provides the largest load factor, and the least amount of road friction, which results in a lesser amount of heat build up, and the best mileage.

Gard

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gemm
Reg. Feb 2005
Posted 2009-04-24 1:40 PM (#103894 - in reply to #103788)
Subject: RE: tire pressure


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Urban legend check: I was at a ride this past weekend that started out on Thurs around 75 degrees. By Sunday it was 100 degrees. I overheard some people saying they were going to release some air pressure from their tires to avoid blow-outs because of heat expansion in the tires. I don't know if they were talking about trailer or truck tires. I didn't do it, and I was nervous all the way home! Were they right?
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retento
Reg. Aug 2004
Posted 2009-04-24 2:16 PM (#103902 - in reply to #103894)
Subject: RE: tire pressure


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Originally written by gemm on 2009-04-24 2:40 PM

Urban legend check: I was at a ride this past weekend that started out on Thurs around 75 degrees. By Sunday it was 100 degrees. I overheard some people saying they were going to release some air pressure from their tires to avoid blow-outs because of heat expansion in the tires. I don't know if they were talking about trailer or truck tires. I didn't do it, and I was nervous all the way home! Were they right? 

Probably not..... The one's that turned air out were probably the ones that had tire problems on the way home. Imagine what that under inflated tire looks like making that short, tight turn at the filling station all the while climbing up and over the curb.... If it don't pull the bead off the rim, then it will probably break a cord/belt in the tire..... It probably won't blow out today, no, it's going to wait untill you're in a big hurry, going to an event, with the kids, all the horses, pick-nik gear, on a Sunday, in the boonies, then all of a sudden that under inflated tire is going to go BOOM...... Hey! GOT....  http://usrider.org/

Keep you tires properly inflated and replace them every 5 to 6 years...

 

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jdzaharia
Reg. Apr 2006
Posted 2009-04-24 2:29 PM (#103903 - in reply to #103894)
Subject: RE: tire pressure



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Originally written by gemm on 2009-04-24 1:40 PM

Urban legend check: I was at a ride this past weekend that started out on Thurs around 75 degrees. By Sunday it was 100 degrees. I overheard some people saying they were going to release some air pressure from their tires to avoid blow-outs because of heat expansion in the tires. I don't know if they were talking about trailer or truck tires. I didn't do it, and I was nervous all the way home! Were they right?

No.  The difference from 75F to 100F is not enough to over-inflate a tire.  Over-inflated tires do not blow out due to heat.  Under-inflated tires blow out due to heat.  But, not because of the ambient air temperature or because the pressure gets too high.  Under-inflated tires blow out due to heat build-up in the rubber caused by excess flexing.  Like retento said, the people who let air out of their tires at 100F probably are the ones having tire problems in the first place.

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jdzaharia
Reg. Apr 2006
Posted 2009-04-24 2:38 PM (#103904 - in reply to #103788)
Subject: RE: tire pressure



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I always go to the max pressure printed on the tire.  But, there used to be a member here that recommended following these charts:

http://www.goodyear.com/rv/pdf/rv_inflation.pdf

 

While we're on the subject, what does everybody think of this?

http://www.goodyear.com/rv/pdf/marathon_gen_info_032806.pdf

Goodyear says that industry standard says the trailer tires are rated for 65 mph at the max pressure, but if you want to run up to 75 mph, you can increase the air pressure by up to 10 psi over the rated pressure, provided your wheel will handle it.  Does anybody actually over-inflate their tires in order to run at higher speeds?

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Tresvolte
Reg. Feb 2008
Posted 2009-04-24 3:16 PM (#103907 - in reply to #103904)
Subject: RE: tire pressure




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Location: Where the wind comes sweepin' down the plain...
Originally written by jdzaharia on 2009-04-24 2:38 PM

I always go to the max pressure printed on the tire.  But, there used to be a member here that recommended following these charts:

http://www.goodyear.com/rv/pdf/rv_inflation.pdf

I agree with the chart. The lower the pressure the less rating that you have. If you know you are carrying less than max weight, you could lower your pressures  for a smoother ride. Most people don't know their weights well enough or pay enough attention to do this. Me personally, I am going to check it cold and inflate to the cold max everytime. I'd rather be safe on the load rating.

Originally written by jdzaharia on 2009-04-24 2:38 PM

While we're on the subject, what does everybody think of this?

http://www.goodyear.com/rv/pdf/marathon_gen_info_032806.pdf

Goodyear says that industry standard says the trailer tires are rated for 65 mph at the max pressure, but if you want to run up to 75 mph, you can increase the air pressure by up to 10 psi over the rated pressure, provided your wheel will handle it.  Does anybody actually over-inflate their tires in order to run at higher speeds?

I hadn't ever seen this. I don't pay attention (although I should) to the max speed rating. I know that they are there and I know that I am running it faster than rated, but when it comes to load, I tend to overkill on my tires...so theoretically if I inflate to cold max, I am good to 2730 going 75 mph vs. 3000 at 65 mph on a Marthon tire. I only have one trailer that I use very much that it would make much difference, but I don't use it long hauls. 50-75 miles at a time. Kind of evens out, don't you think?

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gard
Reg. Aug 2007
Posted 2009-04-24 4:20 PM (#103909 - in reply to #103788)
Subject: RE: tire pressure


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I run truck tires on my trailers, so I don't pay attention to the speed ratings of ST trailer tires. If my truck is safe at speed, so will be my trailers.

I've been to many schools on tire maintenance. They were directed and taught by the FAA, various tire manufacturers and my employer. They all agreed on several points:

1) More damage is done to tires by under inflation than over inflation.

2) The heat damage to the sidewall bead area laminations is irreversible.

3) The cord areas are more subject to physical damage with low air pressure

4) In extreme low pressure, overloaded circumstances, the sidewalls can be damagedt by the rims.

5) Any tire that has been used with under inflated pressures (these pressures will vary according to the ply rating) are subject to change, will not be reused, and have holes drilled in them to effect a scrap value.

6) Once your maximum cold pressure has been satisfied, the air pressure should not be readjusted

Gard

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PaulChristenson
Reg. Jan 2007
Posted 2009-04-24 5:47 PM (#103915 - in reply to #103802)
Subject: RE: Latent Heat of Evaporation


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Originally written by Tresvolte on 2009-04-23 9:45 AM

Originally written by PaulChristenson on 2009-04-23 1:36 AM

The cold pressure is a maximum

I read this all the way through three times...are you recommending not to use the maximum cold pressure, or to use the maximum cold pressure?

The rest of the explanation is WHY... A math/physics degree is a terrible thing to waste...

Edited by PaulChristenson 2009-04-24 5:49 PM
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gemm
Reg. Feb 2005
Posted 2009-04-25 11:35 PM (#103952 - in reply to #103788)
Subject: RE: tire pressure


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Thanks you guys! Now I'm really glad I left my tires at their regular inflation. I didn't see any trailers pulled off the side of the freeway, so I hope they all got home.
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BlazingCreekBar
Reg. Nov 2008
Posted 2009-04-26 4:50 PM (#103975 - in reply to #103788)
Subject: RE: tire pressure


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Some of these posts, well depending who you are all of these posts, are very meaningful. This was one of those to me. After correcting all my tire pressures and hauling this weekend I noticed the difference. Not that things seemed bad before, however they were definitely improved. Why didn't my oil change guy properly load my vehicles tires? Why was my trailer PSI so low. Well now we are on board and riding fine. Thanks DAVE for hosting this forum!

Edited by BlazingCreekBar 2009-04-26 4:52 PM
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Tresvolte
Reg. Feb 2008
Posted 2009-04-27 8:00 AM (#104011 - in reply to #103915)
Subject: RE: Latent Heat of Evaporation




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Location: Where the wind comes sweepin' down the plain...
Originally written by PaulChristenson on 2009-04-24 5:47 PM

Originally written by Tresvolte on 2009-04-23 9:45 AM

Originally written by PaulChristenson on 2009-04-23 1:36 AM

The cold pressure is a maximum

I read this all the way through three times...are you recommending not to use the maximum cold pressure, or to use the maximum cold pressure?

The rest of the explanation is WHY... A math/physics degree is a terrible thing to waste...

That's funny...true, but still funny. That is the way I read it, but I kept thinking I was missing something. I guess I had several Mondays last week.



Edited by Tresvolte 2009-04-27 8:01 AM
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ridingarocky
Reg. Aug 2008
Posted 2009-04-27 12:17 PM (#104026 - in reply to #104011)
Subject: RE: Latent Heat of Evaporation



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Originally written by Tresvolte on 2009-04-27 8:00 AM
Originally written by PaulChristenson on 2009-04-24 5:47 PM

Originally written by Tresvolte on 2009-04-23 9:45 AM

Originally written by PaulChristenson on 2009-04-23 1:36 AM

The cold pressure is a maximum

I read this all the way through three times...are you recommending not to use the maximum cold pressure, or to use the maximum cold pressure?

The rest of the explanation is WHY... A math/physics degree is a terrible thing to waste...

That's funny...true, but still funny. That is the way I read it, but I kept thinking I was missing something. I guess I had several Mondays last week.

Thanks to ALL for the replies... As to Mr Christianson.. Now i know why I never excelled at math or physics... I, too read your reply 3 or 4 times.. While i got the gist of your answer.. I got bogged down in the why!!  By the way, the weekend ride was fun and I had no problems, tire or otherwise.. Leslie

Edited by ridingarocky 2009-04-27 12:19 PM
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