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Old 04-04-2015, 03:01 PM   #1
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Run TT tires with less than max pressure?

We have many campfire discussions on this subject. My 95 34' AS is getting new axles, 3500#. The trailer loaded for the road weighs 9700# on the CAT truck scales. I have E rated tires on it (6X2800#=16,800#) therefore the load carring capacity of the tires is more than the trailer weighs.

What are the consequences of lowering the tire pressure to less than 80psi in order to soften the ride?

The new axles haven't been installed yet, but surely will dampen the road. The original axles are shot, no movement what soever.

Four of the tires are less than 6 months old, other two are 2 years old.

Are there advantages/disadvantages to using D rated tires at 60psi?

Welcome your input.
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Old 04-04-2015, 03:31 PM   #2
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I'll bet there is a load table somewhere on the manufacturer's website that would tell you the appropriate pressure for a given load. I would be very comfortable following those recommendations.

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Old 04-04-2015, 04:10 PM   #3
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We have the Michelin LT tires that AS ships on the newer higher-end trailers and the load tables indicate that we could inflate to 45 psi and still be safe. I inflate to 55 psi for a margin of safety. The benefit is a softer ride for the trailer which means fewer popped rivets and less wear and tear on the trailer and its cargo.

There are lots of threads on this subject in the forum. Some of the comments on those threads are by informed people and others are by less informed people. It's pretty easy to identify which type is making a particular comment.

I would use the "search" function and read up on this subject so you can feel confident in whatever decision you make.
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Old 04-04-2015, 05:00 PM   #4
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I just posted my experience with TTs, 80 PSI and heavier axles thought you might like to see along with evidence of how smooth it rides.

http://www.airforums.com/forums/f437...ke-133219.html

http://www.airforums.com/forums/f439...-133041-2.html
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Old 04-04-2015, 05:33 PM   #5
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David,

We've been running with 80 PSI with our 16" Michelin LTs and had similar experience as concerns leaving objects out on counter tops and were amazed to fnd that they did not move on a recent trip to Sebring. I do not know the rating of the original axles that my 2011 Classic 30 comes with. I can't help but feel that part of this is due to the adjustment of the WD bars on my Pro Pride. I would really be interested to find out what advice Switz would have on this subject.

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Old 04-04-2015, 06:19 PM   #6
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The per tire load on a tridem is quite different than for a tandem. E-rated really was overkill, assuming weight readings per wheel do not show large discrepancies.

A commercial LT tire such as the Yokohama RY-215 or Andrew Thomsons specific Michelin LTX recommendation would be better.

The load index would be more appropriate.

Full sidewall pressure is always best. The Load & Pressure Tables are not applicable to trailer use.
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Old 04-04-2015, 08:12 PM   #7
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Finally, someone who knows that to realize the capacity of a given load range tire, one has to inflate to the maximum pressure!
That being said, on our 30' Excella, with the original Goodyear Marathons, inflated to the magic 60 PSI, we have always managed to blow out tires, in fact, rather consistantly.

Since then with LR "E" Carlyles, inflated to 80 PSI, there have been no problems. I have an AirSafe system, which gives the AS a "soft" ride, and no problems with popped rivets, etc.

I just finished a 1996 34' remodel, also installed LR "E", on it, and will do the same thing. It's easy to "overthink" things. If it ain't broke, don't fix it.

Larry


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Originally Posted by slowmover View Post
The per tire load on a tridem is quite different than for a tandem. E-rated really was overkill, assuming weight readings per wheel do not show large discrepancies.

A commercial LT tire such as the Yokohama RY-215 or Andrew Thomsons specific Michelin LTX recommendation would be better.

The load index would be more appropriate.

Full sidewall pressure is always best. The Load & Pressure Tables are not applicable to trailer use.
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Old 04-04-2015, 08:20 PM   #8
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Larry - aren't those D load Marathons supposed to be at 65 (not 60) PSI? Those 5 lbs under could be connected with multiple failures, I think...

65 PSI to get the 2540 per tire and 65 MPH max speed limit (I know yo can go to 75 MPH with 10 more PSI but load does not increase...).
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Old 04-04-2015, 09:32 PM   #9
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Are you guys checking tire temps with infra thermometers. If they run hot they will blow.

If I remember correctly you don't want your tires getting over 135°F. As I remember in summer tire temps get to about 122° check temps on all tires, if one is getter significantly hotter than the rest you better check air pressure.
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Old 04-04-2015, 09:43 PM   #10
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I recently had 6 Commodore 225/75R15's on our 1987 Avion 34W. They achieve 2540 lbs per tire at 50 psi.

I look forward to seeing how these tires perform on the Avion.
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Old 04-05-2015, 05:24 AM   #11
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When in doubt, max the pressure out! Peace,jim
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Old 04-05-2015, 07:58 AM   #12
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I run Michelin 16" LT's on our 30' AS. Last summer I thought I would lower the tire pressure a bit in hopes of softening the ride. I dropped the pressure from the max 80 to 55 ( I think). For the first time ever I found severe sway at highway speed. Back up to 80 and as expected, no more sway. So 80 it is for me. I do still find a drawer or two opening and a few things shift around but not as bad as when I had the GYM LT's on it. Ironically we do leave some things on the kitchen counter and they usually stay put unless we are on some really rough roads.

See ya'll on the road sometime.
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Old 04-05-2015, 08:51 AM   #13
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My bad call re the 60 PSI, I found one of my old check lists, and they were inflated to 65 PSI. The real cause of the failures of the GYM's was poor quality tires. I've heard that they have finally solved the problem, I have no idea of what those problems were, but I'll simply not buy them anymore.
I've had excellent performance from the Carlyle "E" rated, so I'll stay with them....

Thanks for calling me on this mistake.

Larry



Quote:
Originally Posted by SteveSueMac View Post
Larry - aren't those D load Marathons supposed to be at 65 (not 60) PSI? Those 5 lbs under could be connected with multiple failures, I think...

65 PSI to get the 2540 per tire and 65 MPH max speed limit (I know yo can go to 75 MPH with 10 more PSI but load does not increase...).
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Old 04-05-2015, 10:23 AM   #14
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There is sound factual engineering evidence to support the need to

1. Get on a scale and using the appropriate worksheet learn the actual load on each tire with the RV at full load, to ensure no tire is in overload. I have read where more than 25% of RVs have more than 400# side to side un-balance. There are probably a similar percent with unbalance axle to axle.

2. Inflating trailer tires to the pressure on the tire sidewall is the best practice available to trailer owners to lower the "Interply Shear" forces on the tire belts. This force can be more than 20% higher in trailers than motorhomes or pickups when turning any corner or radius. It is this force along with the rubber being degraded from the heat from excess speed, low inflation and excess load that exceeds the properties of the belt rubber. This can result in the belt separations seen on many tires in trailer application.

If you want to understand why this "Interply Shear" force is important you can Google the term to read more. You can lower, but not eliminate, it with increased inflation.
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Old 04-05-2015, 10:32 AM   #15
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Thanks for the info. Peace,Jim
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Old 04-05-2015, 11:36 AM   #16
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I would think that a large percent of the people here were not born yet when radial tires first showed up.. The reason they were odd back then is they looked like they were almost flat with a fat wad of tire next too the ground.. They were made to run like that over a bias tire. One reason they got 2 times the tire life is the side walls could flex a little and offset tracking issues.

With that in mind and running Michelins LT on our old Overlander,, I carry about 1/2 the max pressure as the side wall states as they are carrying about 1/2 the rated load.. I want the tires to flex over bridge seams as much if not more than the torsion axles would have too..

If one followed the high pressure movement ,, it all got started with the EPA back in the mid 1970s to raise MPG that 1/100 of a mile per gallon.. For that reason I much better pump another gallon of fuel into the TV every stop than replacing a tv,,, microwave,, or beat out my new axles needless.. FYI I have almost 40k on my tires and they have worn about 30%.. Sodbust
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Old 04-05-2015, 02:36 PM   #17
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Quote:
Originally Posted by Hummer View Post
Are you guys checking tire temps with infra thermometers. If they run hot they will blow.

If I remember correctly you don't want your tires getting over 135°F. As I remember in summer tire temps get to about 122° check temps on all tires, if one is getter significantly hotter than the rest you better check air pressure.
That is interesting.

In the summer around here 120 air temps are not un-heard of during the early afternoons of late June. Getting another 15+ degrees into the tires I would think would be common place

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Old 04-05-2015, 02:47 PM   #18
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My infrared reads commonly 40* above ambient measured between tread blocks at shoulder.
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Old 04-05-2015, 02:55 PM   #19
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I took several tire temp measurements on a trip last year, and the trailer tires were consistently 10 to 15 degrees cooler than the truck tires.

I was at the time trying to determine if any of the six trailer tires were running any hotter than the others, and they were not.
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Old 04-05-2015, 03:09 PM   #20
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I have no idea if I'm running my 16" mich LT tires at the right pressure or not. I have them set to 65 psi cold. My TPMS system pressure increases to a it 75 when warm and the internal temp seems to stay within about 5-7 degree of ambient once it gets to 75 psi. Does that seem about right?
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