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Old 05-16-2016, 11:14 AM   #15
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I sincerely thank all that have posted and commented.
My run up to 80 was brief and in a section of road that was open and flat.

I keep a good eye on my tires and look for signs of delamination, body ply separations, tread separations and other sources of failure in tire design, manufacturing and operation.

What I would like is a straight up answer about how much PSI a tire should contain a cold temp. I understand that running at max inflation decrease sidewall flex but that may be at the cost of tread life at the center of the tire and a stiffer ride than is necessary.

I would love to find a local RV dealer that can weigh each tire load and then reference a chart and make an informed suggestion as to cold pressure.

I have gone to the "Tire Blog" and found it informative, will spend some more time there trying to figure out my PSI.
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Old 05-16-2016, 11:31 AM   #16
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Just for the fun and not to poke a stick in anyone's eye here is a tire pressure setup based on my trailer.

My TT weighs 6500 loaded to go.
My truck supports 720 of that due to tongue weight.
Ergo my travel trailer tires are supporting 6500-720= 5780

I have four tires, if each tire were to be equally loaded (function of weight distribution in TT and how well the WDH is performing) each tire would be supporting 5780/4=1445.

My tires are Trailer King ST 225 75R15 D. Max load is 2540 at 65 psi cold.

H2OSki was kind enough to attach a chart from Goodyear that has a tire rating that matches what I have. Using that chart I get that my tires should be able to support the load at between 25-30 PSI. I have never seen a common use trailer tire inflated below about 45 PSI so what gives?
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Old 05-16-2016, 11:50 AM   #17
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Tireman9, a tire engineer, has told you that with an ST tire, you run the max inflation on the sidewall. I would hope you don't think you know more about this topic than he does.

If you have the exact tire that the Goodyear or Michelin inflation table is designed for, then at least you can complain to Goodyear or Michelin you were following their advice. If you don't, do you think Goodyear will care at all about your tire failure?

You may need to do a lot more reading at the RV Tire Safety Blog before you start trying to do math that just isn't necessary at all.

You do understand that in operating a vehicle on the public roads with possibly under-inflated tires you are putting more than just yourself and your own personal property at risk?
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Old 05-16-2016, 01:05 PM   #18
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Dude! You opened yourself up to the tire police and the truck police all in one thread, gutsy move!!


Anyway, congrats on getting real world weights. As far as the tires, I run mine at the 65 PSI max listed on the sidewall. It makes sense to me, dragging these things sideways against their will in tight corners makes me think so. I am not concerned about tread wear, three years from date of purchase they will be replaced, and with my usage they will probably look pretty new when that happens (assuming they don't explode for one reason or another before then).


I am not a tire engineer (or any other kind of engineer) or even all that smart, so take that for what its worth!
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Old 05-16-2016, 01:27 PM   #19
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If suggesting listening to an engineer over opinions on the internet is considered policing, then please tell me where to go pick up my badge.
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Old 05-17-2016, 12:26 AM   #20
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In reading Tireman9 post on this thread he makes no recommendation about running the maximum inflation on the sidewall of the tire. His post does mention maximum speed ratings. I agree strongly with his advice.


If you go to his blog and kick around you will find this post on his blog site.

RV Tire Safety: What should trailer owners do?

In the above blog he pretty much describes the method I was mulling over plus adding 10% additional pressure. It goes without saying you should not exceed the maximum inflation but I will say it. You should not exceed the maximum inflation.

As for the method of just running full max air pressure I don't have a problem with that. In that case you maybe trade off tread life for a bit of an easier time hossing the trailer around tight quarters. Most trailer tires age out, not wear out, seems to be a common mantra. Having tires that skid sideways easier will help out the bearing life.

Also tires that are inflated to their max may be less likely to inducing trailer sway.

I have always figured that trailer tires, since they are poorly warranted and seem prone to a much greater degree of carcass failure, must be a way that rubber and tire companies work off their misbatched or improperly compounded rubber. Stuff you don't want to put in a passenger tire, light truck tire or other product would be perfectly acceptable in a product no one expects to last anyway. Saves you dump fee at hazardous waste dumps.
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Old 05-17-2016, 10:41 AM   #21
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To be clear. I read the initial question as referring to tire loads and inflation on the TV. Motorized vehicles such as MH or TV can adjust tire inflation with the tire loading part of the consideration.

TT are COMPLETELY different topic. There are structural forces that TT tires are subjected to that can be 24% higher simply because they are on the TT axle rather than on a motorized vehicle. The technical term is Interply Shear. Now for those that want a brief understanding you can read my post on that topic. If you want some more detailed info can read this graduate paper. or simply Google "Interply Shear tires" to see what you find.

TT still need to be weighed to confirm that your unit is not in the majority of trailers with one or more tires or axle in overload. Having confirmed you are not carrying more than 85% of the max load capacity of your tires you can then simply set your cold inflation to the pressure molded on the tire sidewall that is associated with the max laod. This will lower, but not eliminate, the excess interply shear.

The Shear force is a major reason TT tires have a shorter life than tires on a motorized vehicle.

Hope this helps clarify the topic at hand.
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Old 05-17-2016, 11:32 AM   #22
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Thanks for the correction, Tireman9.

I'm guessing my TT front axle is carrying more weight than my rear axle.
From my previous calculations I would have to estimate the front tires are carrying about 1650 pounds.

That works out that my front tires are at 65% of capacity.

I sure wish there was a RV dealership that could weigh tires independently, sure seems to be a need for it.

Would tire construction method play a part in mitigating "interply shear"? The tires on my trailer are built with a nylon cap strip, I am assuming that would be between the belts and the tread cap.
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Old 05-17-2016, 12:38 PM   #23
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RV dealers seem to have a mindset of "the less we tell the buyer, the less we help them make informed decisions, and the quicker we get them out of our hair, the better." Combine that with an attorney somewhere telling management not to do anything that would expose the business to any kind of potential liability risk, and it's a wonder we can even walk the lot before we buy these things.
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Old 05-18-2016, 10:52 AM   #24
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Quote:
Originally Posted by Parrott_head View Post
Thanks for the correction, Tireman9.

I'm guessing my TT front axle is carrying more weight than my rear axle.
From my previous calculations I would have to estimate the front tires are carrying about 1650 pounds.

That works out that my front tires are at 65% of capacity. GOOD

I sure wish there was a RV dealership that could weigh tires independently, sure seems to be a need for it.

Would tire construction method play a part in mitigating "interply shear"? The tires on my trailer are built with a nylon cap strip, I am assuming that would be between the belts and the tread cap.
Check this site for more info on how and where to get individual tire loads.

Yes Nylon cap ply (on top of belts) can reduce the failure rate but does not lower the shear force, just makes the tire more able to tolerate the extra loading. Keeping the inflation up does reduce the forces.
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Old 05-18-2016, 03:01 PM   #25
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Thanks for the link.

In another month or so I will weigh again. Wife and I are still adding/subtracting the things we are hauling.

I messed up and weighed my truck on the steering axle pad and left the drive axle pad unloaded, trailer was where it should have been on the third pad.

I will weigh again correctly, then change the number of links I have in my WDH and weigh again. I am at 11% tongue weight and could easily shift more to the tongue, if that proves beneficial.

I will probably lower the tire pressure to 60 psi front, and that much or maybe a bit less on the rear axles. I tow in Oklahoma and we really get toasty down this way, with lots of old, black, rough asphalt roads.

Lots of geometry and theory to play with.

I need a better hobby....
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Old 05-20-2016, 11:11 AM   #26
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" I understand that running at max inflation decrease sidewall flex but that may be at the cost of tread life at the center of the tire and a stiffer ride than is necessary.

I do not believe that running a tire at designed max inflation would result in increased tread wear at the center area of the tread. Running OVER the max inflation pressure would result in increase tread wear at the center. Might be wrong on this, but its only my opinion...

Joe
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Old 05-21-2016, 10:09 PM   #27
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Well I bled out the air to put all four tires at 60PSI, tires have just a bit of "Radial Bulge" to them, nothing like a TV tire.

On the plus side the LED replacement bulbs came in. I replaced all the overhead lights with warm LED's with the exception of the reading lights which I installed the cool LED's.

Now when I turn on all my lights the cooling fan for the inverter doesn't even come on. Before if you turned on three lights the fan would come on and as you added more lights it sped up. Kind of annoying if you are playing cards.
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Old 05-24-2016, 08:17 AM   #28
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Well I bled out the air to put all four tires at 60PSI, tires have just a bit of "Radial Bulge" to them, nothing like a TV tire.

On the plus side the LED replacement bulbs came in. I replaced all the overhead lights with warm LED's with the exception of the reading lights which I installed the cool LED's.

Now when I turn on all my lights the cooling fan for the inverter doesn't even come on. Before if you turned on three lights the fan would come on and as you added more lights it sped up. Kind of annoying if you are playing cards.

Why are you lowering your tire inflation?
Didn't you understand the post on Interply Shear? I understand that that topic got pretty technical but that's why I offered the summary that the best practice for towable RVs is to run the inflation marked on the tire sidewall that is associated with the MAX load. Anything less will increase the destructive forces experienced by the tire structure.

Visual inspection of sidewall bulge to establish an inflation level is definitely not the proper way to determine tire inflation.
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