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Topic ClosedGVWR>GAWR and Stabilizer Issues
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Topic: GVWR>GAWR and Stabilizer Issues
    Posted: 09 Jan 2019 at 3:15pm
I’ll take a look at mine and see what it’s crown is. My trailer is more or less empty right now too.

Just to be clear deflection is a different analysis from yield stress. Beams will deflect under load and return to their original positions. Think jet aircraft wings. The reason the axles are crowned is so the wheels don’t end up with too much negative camber when loaded. If a beam doesn’t return then it has been overstressed. I’ve not yet looked at the axle deflection calcs yet.
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
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Posts: 5290 		Direct Link To This Post Posted: 23 Jan 2019 at 3:53pm
Things finally warmed up and dried out enough out here on the OBX for me to crawl under my rPod and measure the crown in my 179 axle for comparison to StephenH's new axle. 

I have a definite crown in the axle center too, about 1/4 inch, so my crown is a little less than StephenH's. I probably have a bit more weight in mine that StephenH does (mostly some canned goods), or it could be that my axle has started to fatigue a little bit, or it could simply be measurement error. 

I took a look at the deflection calcs and get about 0.1 inch for an unloaded trailer and 0.14 inch for a fully loaded trailer, so there really isn't a whole lot of change as the axle loading changes.  

Based on this I think if we did proceed to add reinforcing angle to the bottom of our rPod axles we probably should try to get the angles made up with a 3/8 inch crown in them to match StephenH's axle. That way there would be no impact on a new axle's crown or bending stress under light load conditions when we clamped the angle to the axle.  But in reality the deflection changes are going to be small enough that if the crown ends up slightly off its probably not a big deal. 

StephenH, what are your thoughts. do you want to proceed? We live close enough to each other that we might get a benefit by finding a shop to make up two angles for us. 
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Posts: 144 		Direct Link To This Post Posted: 14 Mar 2019 at 6:21pm
Fellas, I have tried to speed read seven pages of axle bending.  Sunday I had my 172  home to spring flush and noticed the tires, both sides wearing on the inter part.  Taken trips from Charleston SC to SD, CO, and three to GA.  Not a whole lot for 2017.  I use equalizer sway bars and carry a heavy suit case, a Cushman Scooter, 2 alum ramps, 2 Hyd. Jack, 2 tool boxes, lawn chair, food for 2 weeks, CD and DVDs.  I know I am transferring some of the weight in the pickup back to the camper. What you have said, if I read correctly, I shouldn't have used the equalizer bars because FR didn't build a sturdy camper.  WinkOne thing bothers me.  No one has said the rubber in the axle is bad.  Rubber doesn't become dis-formed around the inter part of the axle? Wink Second, How do you measure the hump in the axle? 
Thanks to all of you,
Happy Traveling,
Tom
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michaeln View Drop Down
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Posts: 40 		Direct Link To This Post Posted: 14 Mar 2019 at 8:02pm
I am betting that reinforcing the axle is just going to transfer stresses to some other part, and that will end up bending or breaking.
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Posts: 966 		Direct Link To This Post Posted: 14 Mar 2019 at 8:06pm
You guys got me curious, so I went and looked and the axle on my new 171 actually has "CAP 3500#" printed on the label.

The sticker on the trailer has 3000 for the GAWR.
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Posts: 5290 		Direct Link To This Post Posted: 15 Mar 2019 at 1:43am
Originally posted by SC for Huskers

Fellas, I have tried to speed read seven pages of axle bending.  Sunday I had my 172  home to spring flush and noticed the tires, both sides wearing on the inter part.  Taken trips from Charleston SC to SD, CO, and three to GA.  Not a whole lot for 2017.  I use equalizer sway bars and carry a heavy suit case, a Cushman Scooter, 2 alum ramps, 2 Hyd. Jack, 2 tool boxes, lawn chair, food for 2 weeks, CD and DVDs.  I know I am transferring some of the weight in the pickup back to the camper. What you have said, if I read correctly, I shouldn't have used the equalizer bars because FR didn't build a sturdy camper.  WinkOne thing bothers me.  No one has said the rubber in the axle is bad.  Rubber doesn't become dis-formed around the inter part of the axle? Wink Second, How do you measure the hump in the axle? 
Thanks to all of you,


Sorry to hear your having axle problems. 

When you say equalizer bars I assume you mean a weight distribution hitch? If so then possibly you could have transferred more weight back to the trailer axle than you really should. It would depend on how much tension you put on the wdh bars. I suggest that you load up, tension your bars as you normally do, then run through a public scale and get the individual axle weights. That way you'll know exaclty what you're putting on the trailer axle.

To measure the crown/arch/camber on your axle, run a string line between the ends of the axle tube along the bottom of the tube from one side of the trailer to the other and measure the gap between the string line and the tube in the middle.

Yes, I've read that the rubber cords on these torsion axles can get flattened and go bad. But, this would make the wheel on one or both sides sit low, it shouldn't change the wheel camber angle, so shouldn't cause the inside of the tires to wear more, which indicates you have negative camber. That's most likey to be a bent axle tube.  
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Posts: 5290 		Direct Link To This Post Posted: 15 Mar 2019 at 1:47am
Originally posted by podwerkz

You guys got me curious, so I went and looked and the axle on my new 171 actually has "CAP 3500#" printed on the label.

The sticker on the trailer has 3000 for the GAWR.

Yep, makes sense. I'm pretty confident that the lighter rPods are using 3500 lb rated axle just like the heavier ones, they've just derated them to 3000 lbs to limit the total published load you carry. Consider yourself lucky to have some extra margin we don't have on our heavier ones. 
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Posts: 5290 		Direct Link To This Post Posted: 15 Mar 2019 at 1:59am
Originally posted by michaeln

I am betting that reinforcing the axle is just going to transfer stresses to some other part, and that will end up bending or breaking.

How much do you want to bet Tongue?

Seriously though, in this particular case it doesn't work that way. The axle loads are proportional to the distance between the wheels and the axle mounting points, meaning that if you can support the axle tube farther outboard things get better for the axle tube.  That includes the section of axle tube between the supports. 

That's not going to change the loads on the spindle or torsion arms, or rubber cords or any other parts outboard of the axle tube supports, which will see the same loads as before. So if any of those were the failure point before (and they for sure could be in some cases) then they still would be after reinforcing the axle tube. 
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