JBarca wrote:
.......A take away on my part is to get actual individual wheel position loads.......
Exactly!
JBarca wrote:
.......I need to get actual weights and go from there. If this camper setup needs an ST tire capacity of 2,834# or 11,336# total for all 4 tires, there is a large miss in the design. And this is then an industry wide problem.......
This is the conclusion many have reached.
JBarca wrote:
.......This is what I had prior thought, correct or not. This camper is at least built from the factory to have the running gear that will support the entire GVWR of the camper. The GVWR is 10,000# and the tire capacity at max is 10,160#. The truck holds 15% of this weight on the tongue. And if I ever had a 10,000# GVW and 15% is on the tongue, then the running gear should have 15% extra capacity.......
I have made a conservative estimate that individual tire loads vary up to 15% - and if that is the case, then the worst loading on a tire would have NO reserve capacity
JBarca wrote:
.......I was loaded to 7,926# on the axles and my tongue weight is 1,375# for a GVW of 9,301#. So I made a bad assumption I still should have had reserve as I should be able to add still 699# more cargo to reach the 10,000# GVWR. Some split on the tongue, some on the axles.
I am not contesting the fact I need to get individual wheel loads. I will do this and report back. However my camper is at least built with running gear to handle the entire GVWR......
That's not good enough if the individual tire load vary - which we know they do - and that should be factored into the design.
JBarca wrote:
.......Many brands cheap out and declare the truck is going to hold part of the GVWR so they install lighter running gear. If my setup is over, those poor folks do not have chance of not being into issues with ST tires.
In my case you have accurately pointed out a miss in my assumptions and I need to base this on actual wheel loads. Again, I will rectify this. Thank you for showing me this. I see the light!!
Question: Where does the 15% variation in loading addition by wheel position thought come from?.........
I tried to find some data to back this up, and only found a smattering. It's based on a guesstimate on my part - a conservative one, such that I will be on the safe side. I could be wrong and the actual value could be lower, but until I find solid data that contradicts it, I'm sticking with the value.
JBarca wrote:
.......You added the entire water weight to the front axle not accounting for any of it to be spread by the equalizer. I could not follow how you came up with this.....
Again, I was being conservative. I really really don't want to give advice that contains a fatal flaw just because I underestimated some value.
Besides, if I over estimate the size needed, then it's just a bit more expensive - as opposed to a failed tire and the damage that it makes.
JBarca wrote:
....... This is like an additional 15% extra. Maybe I will figure this out this weekend when I weight each wheel location. I have a force jack and can do this here in the yard. With and with out water......
Yes, definitely do that. Actual values always trump estimates.
JBarca wrote:
.......Yes, I know the cost of lab work. I buy forensic metallurgical analysis along with FEA failure analysis often and your $2K is a lot cheaper… LOL However on the private sector $2K is a lot and I can buy a few sets of tires for that cost. Me being me however, I have to at least search this out to make sense of it in my own head before I buy new anything.
Did I understand this correctly, you are thinking the tire loads are what caused the tire bulge?......
There are 2 different questions here. What caused the tire to fail and what can be done to revent a reoccurance. I'm asnswering the second one.
To answer the first one, I would really want to closley examine the tire in question.
JBarca wrote:
....... I respect your opinion and I’m trying to understand that I have not somehow else created a situation other then weight to cause this failure. When a tandem axle TT turns the tires are doing some really strange twisting in the side walls. My thought was that somehow this twisting may have upset the inside of the tire in the tread area or would side turns more affect the side wall construction?.........
If I were confronted with the tire in question, the first thing I would do is have the tire examined with a Shearograohy unit.
Shearography is a non-destructive test where the tire is placed in a sealed chamber and phtotgraphed in an unmounted, un-inflated state. Then a small vacuum is applied to the chamber and the tire is photographed again.
The photos are superimposed over each other (in a computer) and areas of movement are identified. Any area that moves is an area with air trapped inside the tire - a separation. That gives a clue as to what areas are failing.
The normal follow up is to cut the tire in the separated areas to see what components are involved. This might reveal the starting point of the separation.
Typically radial tires fail at the edge of the belts and not the center of the belt.
You mentioned the turning action that takes place in trailer tires and I don't think this would cause any issues with the sidewall - and I'll explain why.
There is a test that the company I work for uses to evaluate belt edge durability. It consists of heat aging a tire (placing a tire in an oven for a period of time) then tesing the tire on a pulley wheel (standard tire tesing equipment), then cycling the tire with varying degrees is slip angle. This stresses the belt edges.
Without the slip angle cycle, the tire doesn't experince belt edge separations, but the varying slip angle does.
So I think this is more a belt edge phenomenon.
I haven't seen anyone report any sidewall failures - except for those normally associated with run flat (air loss) situations.
