Holy Axle Overload Batman!?

[Gyro Gearloose]

I was asked (MidwestCamper) to take a look at why it seems that the more weight is being transfer to the rear axle on a 5'er/trailer.

This has actually been on my mind for awhile so I decided to give it a shot.

I have been doing a lot of CAD drawing of my Reflection 303RLS suspension and saw some strange things when doing some shackle length simulations for Rob F. and some Panhard Bar simulations, as well as a video I saw on YouTube, that seemed to prove what I was seeing in CAD. I am amazed at how it seems that our rear axles are potentially overloaded on a regular basis.

The attached .PDF document is my interpretation of my CAD drawings and what I saw on YouTube. I did not take the YouTube video so I can't totally vouch for what I've seen, you decide.

Braking Action .PDF: YouTube: Lippert Components Equa-Flex and Correct Track in Action!


Please don't shoot the messenger, just trying to put some complex actions together into words and a drawing.

Pat

[howson]

...I am amazed at how it seems that our rear axles are potentially overloaded on a regular basis...

Pat,
To quote the rvtiresafety.net article again, Tire failures usually occur because of cumulative internal structural damage from heat and time. The excess heat comes from the combination of speed/inflation/load.

If what you suspect is true (weight is being shifted back to the rear axles on a regular basis) this could explain some tire failures, too. (Before anyone responds that tire x has less blowouts, etc., let's assume the Westlakes are good at their load ratings but with no safety factor while the other brands do.) The extra load experienced slowly and methodically tears apart the internal structure until the tire structurally fails (comes apart).

Howard

P.S. Impressive work. Glad you're a member of this forum!

[MidwestCamper]

I was asked (MidwestCamper) to take a look at why it seems that the more weight is being transfer to the rear axle on a 5'er/trailer.

This has actually been on my mind for awhile so I decided to give it a shot.

I have been doing a lot of CAD drawing of my Reflection 303RLS suspension and saw some strange things when doing some shackle length simulations for Rob F. and some Panhard Bar simulations, as well as a video I saw on YouTube, that seemed to prove what I was seeing in CAD. I am amazed at how it seems that our rear axles are potentially overloaded on a regular basis.

The attached .PDF document is my interpretation of my CAD drawings and what I saw on YouTube. I did not take the YouTube video so I can't totally vouch for what I've seen, you decide.

Braking Action .PDF: YouTube: Lippert Components Equa-Flex and Correct Track in Action!


Please don't shoot the messenger, just trying to put some complex actions together into words and a drawing.

Pat

Pat,
I've been theorizing this for some time and your mechanical drawings puts this into perspective nicely. Really nice work. I do not have access to programs such as solid works which can show this dynamically with an add on module. Do you have access to such a program?

Those that would be willing to part with the funds to correct this issue, would invest in an independent suspension or a version that uses slipper springs. Its the transfer of forces through the equalizer that raises the front axle and is the primary issue here. Also not only is the rear axle, hangers and springs bearing this excessive load but so are the tires. Would by chance most tire failures be on the rear axle?
The key here since this would be an expensive fix is to keep a reasonable distance to vehicles in front and do not do panic stops. Do not do heavy brake applies in testing your brakes.

[Country Campers]

Pat
Very interesting and informative work. This further peaks my curiosity that I posted in the "data" post about all the years and miles traveled with no such problems.
What has changed?, cheap materials, shotty workmanship?

Brian

[Gyro Gearloose]

Pat,
I've been theorizing this for some time and your mechanical drawings puts this into perspective nicely. Really nice work. I do not have access to programs such as solid works which can show this dynamically with an add on module. Do you have access to such a program?

Those that would be willing to part with the funds to correct this issue, would invest in an independent suspension or a version that uses slipper springs. Its the transfer of forces through the equalizer that raises the front axle and is the primary issue here. Also not only is the rear axle, hangers and springs bearing this excessive load but so are the tires. Would by chance most tire failures be on the rear axle?
The key here since this would be an expensive fix is to keep a reasonable distance to vehicles in front and do not do panic stops. Do not do heavy brake applies in testing your brakes.

Jim,

I am using an old version of Solid Works, but my skills are still not the greatest and doing dynamic simulations especially with the leaf springs could be quite painful. So I just adjust the different springs Loaded Arch manually (just change a number) and do different simulations manually, not to difficult.

Yea, it would be a complete suspension redo to correct this. It would be interesting to see how hard you need to brake to lift the front tire to where it no longer has traction. 50%, 75% etc. ? What this tells us is, that when you really need the brakes, you will probably only have the two rear tires on the ground. and that sucks more if you were in a turn.

[Cate&Rob]

Nice Work Pat!!
This really helps to fit some engineering explanation to the video clip that started this discussion.

There is a slipper spring suspension system created by Sonny Dismuke http://www.rvimprovementsystems.com/...stallation.pdf that isolates one axle from the other. Sonny was at the Elkhart Rally and at least one member of this forum purchased this suspension system. Perhaps those with more specific knowledge on this system will jump in here . . .

Rob

[Gyro Gearloose]

Pat
Very interesting and informative work. This further peaks my curiosity that I posted in the "data" post about all the years and miles traveled with no such problems.
What has changed?, cheap materials, shotty workmanship?

Brian

Brian,

With data collection, it would be interesting to know what tires are wearing first, front or rear? I think I read that Rob's rears were wearing faster and that would make sense. Brakes wearing faster, front or rear etc.

They have been doing this style suspension for years as you indicated. What has changed may not be the issue, but how they are used. Heavier trailers and suspension on the edge of their limits (no designed in overload)? Poor Engineering? Maybe with the Correct Track and the EquaFLex they changed the angles enough to where this problem occurs? Or maybe its just showing up now because of cheap Chinese low quality steel being used and it fails. Or like you are indicating shotty workmanship? Because of such mass of these trailer being produced?

So many variables....

For me I think it's a some of the stuff above, but another part is the old school mentality and changing how things are done to improve the newer designs. Another part is the trailer manufactures don't get a high enough percentage of issues to change and they have to keep the cost of manufacturing down.

If enough data could be collected as you are attempting to do (thanks), maybe a picture can be painted. If you can keep people like me from inadvertently taking it off track.

[Cate&Rob]

I think I read that Rob's rears were wearing faster and that would make sense. Brakes wearing faster, front or rear etc.

Hi Pat,

Actually the other way around. My front axle tires are showing slightly more wear than the rears. I thought that this was counter to our current logic, but Jim (Midwest Camper) suggested that this could be because the front tires are sliding more because they are being lifted. This also makes sense.

I can't see any perceptible difference in trailer disc brake pad wear. All trailer wheels show similar accumulation of brake dust after long distance towing. My trailer brakes are definitely doing their share of the total rig braking. I think the thing we don't know is how heavy does the brake apply have to be to lift the front axle? It seems that most of the time, the trailer braking is shared between the axles.

Before the trailer disc brakes, I would notice that the truck rear wheels would have disc brake dust only when towing. (The truck fronts always accumulate brake dust whether towing or not.) Since adding the trailer disc brakes, there is very little brake dust on the truck rears, indicating that truck front/rear brake balance is not a lot different towing vs not towing.

Rob

[MidwestCamper]

Jim,

I am using an old version of Solid Works, but my skills are still not the greatest and doing dynamic simulations especially with the leaf springs could be quite painful. So I just adjust the different springs Loaded Arch manually (just change a number) and do different simulations manually, not to difficult.

Yea, it would be a complete suspension redo to correct this. It would be interesting to see how hard you need to brake to lift the front tire to where it no longer has traction. 50%, 75% etc. ? What this tells us is, that when you really need the brakes, you will probably only have the two rear tires on the ground. and that sucks more if you were in a turn.

Pat,
One way to do this is to measure the voltage to the brake system and install a string pot to the equalizer or axle. Since this could get expensive, we could make up a scale to install on the equalizer, and record the deflection with video. For the brake percentage, we have the gains so we would need the relationship between brake position and voltage and this relationship to lift.
So at a certain brake position, we could record the lift or rotation of the equalizer. We would then need to measure the voltage at each brake position to nicely fill out a table of voltage to lift. Based on the gain this could be converted to brake position versus lift for a specific vehicle.

[jkwilson]

The weight transfer in that video doesn't worry me nearly as much as watching the spring hanger flexing from side to side. No wonder they break.