Tow rig suspension geometry

Stuntman Autoworks

Stuntman Autoworks

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May 6, 2010
Location
Sanford NC 27330
I have a project in mind for a tow rig which involves a parallel 4 link with panhard bar and airbags.
Suspension gurus I can search all day and find info on geometry numbers for offroading or drag racing but I can't find any good numbers or info to go off of for a good handling suspension when hooked to a trailer. I don't want the rear to rise or squat while accelerating or braking due to bad geometry.
Any help is appreciated.
 
If you want the vehicle to stay flat you need 100% antisquat/dive. Something in the 90s will get you very little movement.

Most people want to set things up for less AS/AD and use socks to control movement. Many factory vehicles are setup with 40-60% AD so that drivers "feel" the movement of the car.
 
The (loaded) trailer has a vertical tongue weight, and a horizontal tow weight, and a CG height, and a horizontal distance from that CG to the hitch and from that CG to the trailer axle. The hitch is at some distance vertically and horizontally on the tow rig, which is where the point of application of all the trailer forces obviously is. All of those things affect dynamic weight transfer from the trailer into the tow rig..

All of those things can be fed into the suspension calcs for the tow rig, but I can't quite wrap my head around how to go about that. I believe you would just need a second set of forces and coords for the trailer weight, so you have your forces that are based on the CG and CG coords of the tow rig, and then forces that are based on the trailer CG and CG coords with respect to the trailer hitch application.

I honestly don't know what good geometry for a tow rig is, I'm just thinking about it in terms of physics and vehicle dynamics and how the trailer forces would affect things.
 
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I’d say get the instant center as far out in front of the vehicle as practical so the line of action slope is pretty flat. AS below 70%. This will make the bumps and inputs from road be put more through the shocks where they can be tuned vs through the links.

Then getting creative with shock valving can help a bunch.

I would say coilovers with air bags.

Set the coilover spring rate for 2” preload for correct ride height when empty, then air bags just to keep at correct ride height and add some spring force when loaded
 
Mac5005 said:
I’d say get the instant center as far out in front of the vehicle as practical so the line of action slope is pretty flat. AS below 70%. This will make the bumps and inputs from road be put more through the shocks where they can be tuned vs through the links.

Then getting creative with shock valving can help a bunch.

I would say coilovers with air bags.

Set the coilover spring rate for 2” preload for correct ride height when empty, then air bags just to keep at correct ride height and add some spring force when loaded
Click to expand...

This was my thought process also, for a future rear suspension. Coilovers with bags. Or large bags and 2.5" tuneable shocks. I like the idea of a metal spring being their incase the bag or line busts when towing.
 
Damn! You beat me to it! I was just gunna say they spelled leaf springs wrong :D
 
Mac5005 said:
I’d say get the instant center as far out in front of the vehicle as practical so the line of action slope is pretty flat. AS below 70%. This will make the bumps and inputs from road be put more through the shocks where they can be tuned vs through the links.

Then getting creative with shock valving can help a bunch.

I would say coilovers with air bags.

Set the coilover spring rate for 2” preload for correct ride height when empty, then air bags just to keep at correct ride height and add some spring force when loaded
Click to expand...

paradisePWoffrd said:
This was my thought process also, for a future rear suspension. Coilovers with bags. Or large bags and 2.5" tuneable shocks. I like the idea of a metal spring being their incase the bag or line busts when towing.
Click to expand...




No coilovers, I want the ability to dump the air so the rear squats for easy trailer hookups or if i'm working off the back of the flatbed I can lower the work height.
 
Stuntman Autoworks said:
No coilovers, I want the ability to dump the air so the rear squats for easy trailer hookups or if i'm working off the back of the flatbed I can lower the work height.
Click to expand...

bags and tuneable shocks should be you net a good ride both loaded and unloaded.
 
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