Hi CapriRacer, Finally getting this this response. Thank you for your thoughts on the tire bulge. I’ll comment below on the loads.
CapriRacer wrote:
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I am also going to take issue with your math - AND EVERYONE PAY ATTENTION!! I have seen others do this type of math and I think there is a hidden pot hole there.
The principle is that for tire loading you want the absolute WORST loading. The load an individual tire experiences is NOT the average. Tires don't average out the load and neither should you.
Yes, you are correct. I made an assumption, bad this I know, that I had enough reserve and I may not. I will correct this. A take away on my part is to get actual individual wheel position loads. I will do that this weekend as I need to hook up the truck to get the WD effects on included.
CapriRacer wrote:
First you said the axle loads were 7660, but added that the water tank adds 266# more axle load. Why didn't you add that to the axle loads? Why did you use the 7660# for your calculation as is when you already know the side to side loading is different? What about the front to rear loading difference?
There is a slight misunderstanding from my post based on your response. Sorry I was not more clear. I stated this.
JBarca wrote:
- Axle weight scaled at 7,660# with no water. When I fill the fresh tank over the front axle it adds 266 # more axle load.
My statement was meant that I have a weight slip at 7,660# which includes WD transferred from the truck. Not included is when I carry fresh water which is over the front axle which adds 266# more. The equalizer moves some of this but I do not know yet what that is.
I then stated this which you may have missed:
JBarca wrote:
- LRD tires have 2,540# load at 65 psi. X 4 tires = 10,160# of tires against a scaled axle weight of 7,926#. Or 2,234# of reserve capacity.
Here I did include the water weight. 7,660 + 266 = 7,926# as I expressed above against 10,160# of tires. So yes, I did include the water. However regardless, I do not yet have individual wheel location weights and I need to rectify this.
CapriRacer wrote:
OK, so I'm going divide the axle loading by 4 to get 1915#. Add 133# for the water = 2048. I estimate that there is a 15% variation in loading by wheel position, so the worst case is 2409# - and I recommend a 15% reserve, so the tire should be capable of 2834#
That mean an ST225/75R15 Load Range D is about 12% under that value.
I'd recommend going up to a Load Range E and 80 psi as the inflation pressure.
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 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 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. 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? 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. 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.
CapriRacer wrote:
JBarca wrote:
......Before I buy anything new, I need more research into why my tire failed and what to buy to help not have the same problem then next time.........
To do that you'll need to take the tire off the vehicle and PAY a tire forensics specialist about $2K. That's the going price.
But if you are willing to accept educated guesses that are worth the price you paid - tire is too small (based on my analysis earlier)
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? 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?
Thanks for your time on this. Greatly appreciated.
John
