Cantilever Rear Suspension. Fab it for my 80 after my turbo build?

[Delancy]

It's a home-designed and built car. It was designed from scratch in solidworks

Beyond philanthropy, what role did you play in the project?

Yes, a very baited question, but ain't that lure nice and shiny?

 

[ChiTown]

There is an 80 over at racedezert that has cantilever front and rear suspension.
http://www.race-dezert.com/forum/threads/toyota-fj80-mid-engine-crawler-prerunner.118641/

 

[Heckraiser]

Beyond philanthropy, what role did you play in the project?

Yes, a very baited question, but ain't that lure nice and shiny?

Mainly scratching my head, turning wrenches and s***-talking the designer of the car. I gave my input where I could, but most of the design decisions came from reading books and doing math

 

[DylanICON]

I was saying if you engineered your own solution, the arms on the bell crank are a ratio of "being pushed/pushing" so if space requirements dictated that you could only use say a 3:1 ratio because you couldn't fit something else under there you would have to multiple spring rates by 3x.

If you did a 2:1 ratio it would be 2x, etc etc. But you obviously won't have the room for 1:1 or else you would just use the shocks as intended.

There are some serious mathematical equations that need to happen to calculate spring rate based off of corner weight and the simplest is based off of the degree of inclination of the shock attached to an axle and a frame:

Shock Angle Angle Correction Factor (ACF)
10° .95
15° .93
20° .88
25° .82
30° .75
35° .66
40° .59
45° .50

But once you start having the axle actuate a bell crank at an off angle which in turn actuates a spring through an arc in a ratio that has not be determined you have a whole lot of serious engineering or trial and error that is going to happen.

Actually the to get the equivalent spring rate in a leveraged situation it is the length ratio squared.
(L1/L2)^2
This is because you are loosing the force in the lever AND you are also loosing the displacement in the lever to build force in the spring.
3:1 lever ratio requires 9x the spring rate so 500lb/in would be 4500lb/in
2:1 would be 4x so 500 would be 2000
both are unrealistic springs
this is why you will rarely see ratios even close to 2:1 except on dirt bikes where the desired wheel rate is in the 20-50 ish range

The problem with ACF is that it changes when you cycle it through large amounts of travel. usually where you are able to package the components gives you a falling rate curve which is opposite of what we want. this actually happens in the stock rear shock placement on an 80 and is why we put a bump zone in the shock in the last couple of inches that bumps the valving up 20%

it is also very difficult to design a cantilever that does not have a falling rate also.

coil overs are not all they are cracked up to be if misapplied.

 

[freshspecbluegt]

There is an 80 over at racedezert that has cantilever front and rear suspension.
http://www.race-dezert.com/forum/threads/toyota-fj80-mid-engine-crawler-prerunner.118641/

I thought of this build right away. He started a post in the Hardcore section here too, think it also made it over to Pirate (hell if I built that I would show it off all over as well)

https://forum.ih8mud.com/threads/luxury-crawler-prerunner-fj80-mid-engine.743737/

That build is completely tube so the packaging wont work on a stock bodied truck but it looks cool

 

[Booger weldz]

Build it 1:1 with 12" shocks and deal with dialing in the camming action as Dylan mentioned.