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Old 01-30-2014, 10:14 AM   #15
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Originally Posted by Ag&Au View Post
Everybody has a theory and/or idea. There's obviously a "perfect pressure" for any given set of conditions. However, conditions change frequently. There is a very long informative set of posts by a tire engineer on another thread, that explains why you can not use the pressure vs load tables without a correction factor for a truck tire when it is used in trailer service. My answer is to use the sidewall pressure. However you will find some contentious threads on this subject. I always use 80 PSI.

Just a point, 80 PSI is not the max rated pressure for the tire. It is simple the pressure at which it is rated to carry the max load. There is a difference. This is also explained elsewhere. I would recommend that you review the posts by user Capriracer. He is a tire engineer. Below is a link to his posts. This will get you to a bunch of threads on tires also.

http://www.airforums.com/forums/sear...archid=2599800

Ken
Ken, spot-on
Btw, I am afraid the link doesn't work as you intended.
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Old 01-30-2014, 10:28 AM   #16
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This was a pretty good thread.

http://www.airforums.com/forums/f438...se-108451.html
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Old 01-30-2014, 10:42 AM   #17
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That's weird, it works for me. Are you logged in? I'm guessing you are.

I got that link by searching the member list for "Capriracer". Then went to his profile page, Clicked on statistics and then "the find all post by him" link. What I posted is the URL for the resulting list. Maybe it only works for me because that page is cached on my computer.

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Old 01-30-2014, 10:48 AM   #18
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Keep in mind that thread is not specifically directed to LT tires on trailers. I have to run to an appointment right down, so I don't have the time to find the one I'm thinking about. I don't believe it's this one.

Ken
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Old 01-30-2014, 11:03 AM   #19
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80 PSI Not Max Pressure?????

I think if you take the time to read the specs on the side of the tires or go to the tire rack website you will find that 80PSI is this max recommended air pressure for the 16 inch Michelin LTX by the mfg that builds the tire.
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Old 01-30-2014, 11:21 AM   #20
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I think if you take the time to read the specs on the side of the tires or go to the tire rack website you will find that 80PSI is this max recommended air pressure for the 16 inch Michelin LTX by the mfg that builds the tire.
I have taken the time to read it many times. perhaps you need to read it again to understand what it says. This in a way is a matter of terminology. The side wall of the tire states a max load for the tire and the pressure necessary when carrying that load.

It does not say that is the maximum safe pressure for the tire and in fact it is not. However they do not commonly publish the maximum pressure because it is not of value to the user, because you shouldn't exceed the max load.

I find you choice of words (the highlighted ones) offensive and unnecessary to state your point.

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Old 01-30-2014, 12:11 PM   #21
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Taken from Michelin website on how to read a tire sidewall.

Every tire made has the maximum mfg air pressure printed on the sidewall in this case 80 PSI.Also on the side wall is the stated max load in lbs which the tire is rated to safely carry when inflated to the max pressure stated ( this is also stated in a two digit code again on the tire sidewall as referred to below.The example below has the code 97 printed on this particular tire of example.
Sorry did not mean to hurt your feelings and I am not trying to make a point.Just trying to help those unfamiliar with reading a tire sidewall.




Load Index

This indicates how much weight the tire is certified to carry at maximum safe inflation. It doesn’t mean 97 pounds, because it’s actually an assigned value that corresponds with its “actual” load capacity found on a load index chart. If you look up 97 on the chart, you’ll find 1,609 pounds. (To see the load index chart on the Tire Speed Rat
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Old 01-30-2014, 12:18 PM   #22
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Tire pressure

I run mine at 60 lbs. I tried them at 80 and the bathroom cabinet sliding doors came out of their tracks. Things don't bounce around so much at 60. I looked at the Michelin tire pressure chart for the tires and 60 lbs is well within the load rating for my 2005 25' safari LS.
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Old 01-30-2014, 12:23 PM   #23
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How to Read Your Tire Sidewall

Tires have many letter and number codes moulded into the sidewall. These codes indicate the tire's size, speed rating, maximum rated load and inflation, tread wear, traction and temperature labelling, materials used and the Tire Identification Number.
The following explanations of Figure 2 start at the top left of the tire with the size, and follow the labels clockwise:
A. Size Description

An example of tire size for a car might be a P215/65R15 (you‚€™ll find these numbers moulded or printed on the sidewall). They mean:
  • P "passenger" cars and most vans and light trucks will use 'P' series tires, although some may use a heavier tire designed for light trucks (.LT.)
  • 215 . the width of the tire from sidewall to sidewall in millimetres
  • 65 . the aspect ratio (sidewall height divided by tire width) in percent
  • R . radial construction
  • 15 . the diameter of the wheel in inches
B. Service Description:

The combination of the speed symbol (rating) and the load index moulded on the side of a tire is known as the service description. (Figure 2 "89H"). Because the maximum tire load capacity is also moulded on the sidewall, the load index is used as a quick reference.
Individual motorists who think that their driving characteristics vary considerably from the average should consult a tire professional who can advise on alternative tire choices for any vehicle. There is no fuel economy benefit in going to a higher load rating - in fact the added weight of the tire can increase fuel consumption. Don't economize on the load rating either - overloading the tire may reduce vehicle stability during hard cornering or stopping. The tire will also wear out prematurely. Also, when replacing speed rated tires, the same or higher speed rating tires should be used. The driver's safety could be compromised by the choice of tires with a speed rating less than what the vehicle was originally equipped with.
C. Load Index

The load index (Figure 2 "89") is an assigned number ranging from 0 to 279 that corresponds with the load carrying capacity of the tire; that is, how much weight it is certified to carry at maximum inflation pressure. Most passenger car load indexes range from 75 to 105, although some tires carry more. The rating can be matched against a load index chart to determine corresponding maximum weights. A load index rating of 89 indicates a maximum load of 580 kg. (See Table 1.)
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Old 02-01-2014, 05:17 PM   #24
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Vehicle manufacturers set tire pressures. Tire retailers/dealers are allowed to set tire pressures for plus sized replacement tires. However, their reference for doing so is the vehicleís federal certification label/tire placard. Therefore the minimum tire pressure for replacement tires is that pressure required to obtain a load capacity from the replacement tires equal to or greater than that provided with the OE tires.

Remember, the DOT, via regulations, directs vehicle manufacturers to set recommended (cold) tire pressures and put those recommendations on the Federal certification label.

Thatís how itís supposed to be none. Many owners follow the directions of others that donít support their own vehicle manufacturers knowledge and authority to set tire pressures. Under inflated RV trailer tires are the primary cause of early failures. Right up there with under inflation is over loading.

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Old 02-02-2014, 08:29 AM   #25
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Follow the charts

I'd suggest following the load charts for ST type tires which should be used on trailers for the safety they were engineered to deliver. The use 5 psi more to allow for regular pressure loss.
It is the air in the tires that's carries the load so more load more air, less load less air. Ride should correspond accordingly if charts are followed. The tire only provides traction and the ability to hold the air required to carry the load plus come specialty jobs such as stable side walls to improve straight pull and prevent fish tail. In the case of the LT or P type on the tow vehicle the softer sidewall engineered for smooth ride is not always safe if used on the trailer. Also for some that may attempt to use the P type on a trailer (I'd not recommend this considering it unsafe) the load charts of the P must be de- factored by 10% when used for anything other than passenger service.
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Old 02-03-2014, 06:17 AM   #26
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I'd suggest following the load charts for ST type tires which should be used on trailers for the safety they were engineered to deliver. The use 5 psi more to allow for regular pressure loss.
It is the air in the tires that's carries the load so more load more air, less load less air. Ride should correspond accordingly if charts are followed. The tire only provides traction and the ability to hold the air required to carry the load plus come specialty jobs such as stable side walls to improve straight pull and prevent fish tail. In the case of the LT or P type on the tow vehicle the softer sidewall engineered for smooth ride is not always safe if used on the trailer. Also for some that may attempt to use the P type on a trailer (I'd not recommend this considering it unsafe) the load charts of the P must be de- factored by 10% when used for anything other than passenger service.
I'm going to disagree.

If you are going to use the load tables for tire pressure, keep in mind what is posted is a MINIMUM (even says so!). Good practice is to use MORE pressure than the minimum. I recommend 15% more.
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Old 02-03-2014, 06:56 AM   #27
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Maximum sidewall pressure is the single "safe" number from which to work (given that the wheel is a match). Any trailer has the tendency to try and tear the tire from the wheel; more so with tandems and tridems. This is the inherent dilemma we face in trying to find the most reliable trailer tire, that the load index can be higher than needed (actual load + 15% or so) and pressures seem excessive for replacements to ST tires.

I'd place a trailer being rattled as a concern of little weight versus the loss of one or more tires at speed. Those consequences involve life & limb, first, and loss of one or both vehicles, second.

Weigh it. Adjust loads as well as possible via wheel position weight scale values. See to the running gear balance, and that torsion arm axles aren't worn out as well as having dead-certain trailer axle alignment. Ideal bearing pre-load. Get the maximum almount of WD onto the trailer that good practice allows. Stick to premium tires.

But respect that the brand or tire type has nothing to do with the need for maximum sidewall pressure when in trailer service.

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Old 02-04-2014, 07:11 AM   #28
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Caprisracer and my viewpoint may not be far apart if the charts show 50 psi is required, the 15% is within 2 pounds of the extra 5 I use.
My suggestion agrees with slowmover that without weighing first the proper air pressure could be a mute discussion.
If you don't know your trailer weight the safest pressure is the max as shown on the tire's sidewall....but why would someone not want to know the weight?
An industry like trucking pays very close attention to this.
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