custom built spec lift trailer build/calculations

[fattyJr]

Hello out there,

I have accessed this website from time to time when I have been bouncing ideas around for things I am building.

Anyway, I have a question/problem I am trying to work out in my head prior to building.

I am building a spec lift for use by my father to recover/transport vehicles behind his silverado truck. He only plans to use it from time to time, but would be a god send when he has it.

I have got a purpose built spec lift OFF an retired recovery vehicle that has hydraulic lift and powered in and out to assist loading.

I have got 2 rubber torsion suspension axles I plan to use that are rated for 4000lb each.

spec2.jpg

The pointed end is the hitch to the truck and is 60" to the centre of the load path. the opposite end (rear) is where the vehicle wheels sit which is 60". the lift it's self is a inverted T shaped arm hanging off the the bottom of the T. One side is extended back for the vehicle wheel to sit on and the other side is connected to a hydraulic ram to raise or lower arm.

I worked it it out I have about 6600lb suspended on the pivot. I would like to run 95% of the weight on the axles with 5% transferred to the truck for stability and due to max weight by tow rules. where would you position the axles under the load path to get this 5% transfer.

If you require more pics, Let me know and I'll send them as I am using google sketchup to rough draw

[PinkertonD]

Hi, I am a little confused on where you are measuring from and to. Can you provide a sketch showing a typical vehicle wheel loaded on to the trailer.

The 6600-lbs is based on what?

Is that the max rated load?

Do you have any pics or websites of an actual trailer you are trying to emulate?

If the loaded-vehicle wheels are positioned behind the trailer wheels, I can't see how you will ever get a positive weight at the hitch end. Maybe I am not understanding what you are trying to do and a few pics of an actual trailer would help immensely.

[fattyJr]

Yea it's rather awkward to explain really. I have some pictures below of a similar spec lift to what I have
spec1.JPGspec2.JPGspec3.JPG

in the pictures the lifting ram (multi stage) is mounted at the bottom. I worked out (might be wrong) that a 3300lb load at the closed lifted position of spec lift IE like below

spec4.JPG

I would have a downward load on the pivot of 6600lb (might be wrong). The lifting ram thrust/load will be into the drawbar of the trailer. If I mount the pivot pin directly over the centreline of the tandem axle Or slight forward of the CL of the axles, 95% of the weight should be taken on the trailer axles and not the towing vehicle. By the way this in not my first trailer.

here is one of my other trailers It's a 6 ton 3 way tipping trailer
trailer1.jpg

I will get my sketch book out and do some drawings as a picture speaks a million words.

[PinkertonD]

OK, I will await further sketches. But making assumptions on your later description, the lifting ram pivot or mounting point will not transfer the load on to the vertical center line between the trailer wheels, just by lifting the vehicle.

While any load that is positioned behind that vertical center line will still see the trailer wheels as the effective fulcrum point. That will always provide and upward reaction at the hitch end. The opposite of what you need for safe towing.

For the sake of better understanding, you can ignore the lifting mechanics and just view the entire trailer as seesaw. Unless you can move the towed vehicle front wheels forwards of that vertical center line, there will always be an upwards reaction at the hitch.

[RWOLFEJR]

Sounds like maybe a tow dolly that incorporates a lift? Maybe to save winching it up on?

Attachment 332

Stumbled on this and had to share... How crazy is thin nutball?

Attachment 333

"Jane...!!! Stop this crazy thing...!!!"

[PinkertonD]

Bob, that is from a company in Germany. They apparently have a small fleet of Goldwings thusly outfitted. The trailer folds up into the nacelle on the back and they can get through choked freeways because it is all so narrow until deployed.

Also, good point with the dolly. Instead of lifting the disabled vehicle, just winch it up onto the dolly until the front wheels are a little forwards of the dolly-axle. When I load heavy stuff (lathes, mills, cars) on to my car hauling trailer, I measure the gap from the hitch-tongue to the ground. Then push/drive/whatever the load is until the hitch-tongue has dropped by 2". Works out pretty close to the desired 10%.

[fattyJr]

I got a rough drawing for you guys to look at

test1.jpgtest2.jpgtest3.jpg

[PinkertonD]

Re-read post #4.

[fattyJr]

I know exactly where I am heading with this now.

Now I have done the drawing, I can see the load paths and how to deal with them.

Will post up pics when i build it