Figuring out Long Travel Suspension - Part 1: Front Bulkhead
The stock suspension on the 150R is comfortable, but not very capable over rougher terrain in my opinion. Suspension travel at the wheels is about half of what I want for this build.
The stock control arms use unsymmetrical pivot points, with heim joints to compensate for the misalignment. I can see the reasoning behind this design. It's an inexpensive and easily manufacturable way to put the front tires where they need to be, while giving extra foot room, with decent travel.
I'm not worried about making more of these, or getting costs down. So I'm free to overcome some of the stock limitations and make this a true long travel system.
Design Parameters:- Target pivot range: 45°
- Target vertical travel: Between 12" to 16" (Stock around 6")
- Maximum overall width: 57"
- Ground clearance: 12" with 225lb driver at 15° rest angle
I own my own private riding properties, so I'm not worried about trail regulations on width. But, I want to be able to trailer the buggy, so I need to keep total width below 57" maximum.
Mocking it up
Keep in mind that everything in this post is "mock up". I'm working out the dimensions and geometries first, and will come back later to make final reinforcements, bushings, and hardware.
Modular Bulkhead:
I'm a big fan of modular design. I want to avoid welding to the frame as much as possible, mostly for convenience and ease of mocking things up and making changes later. Let's work out a bulkhead design that can be easily removed and upgraded later if need be.
Didn't take long. This is just one plate of 4 that will make the bulkhead, but for now will work well to confirm dimensions.
The stock control arm pivot points are 10" top and 12" bottom, and spaced 4.5" vertically. We'll use the existing control arm pivot points as our mounts for the bulkhead, and relocate the new A-Arm much closer to the center. 4" horizontally, and maintain the stock 4.5" vertical.
The purpose of moving the pivot points closer to the center is to allow us to make the A-Arms as long as possible. Longer A-Arms result in more travel at the wheel for every degree of pivot.
Cutting it on the CNC plasma looked like this:
Cooked up in 1 minute and 14 seconds.
The mounting turned out as expected. The bulkhead plate bolts right into place, no welding.
18" A-Arms:
After a little math, I decided I wanted to try 18" A-Arm length. A-Arms on 150's are usually less than 13".
The mock A-Arm was made from American 1.5" cold rolled DOM tube with 0.120" wall thickness. It's some heavy stuff. I plan to do the same for the final A-Arms.
I turned down an insert from 1.125" round as a bung the temporary heim joint. This is just to mock up, as I'm not a fan of heims and don't want to use them on this build. I'm going to replace the heim joint with something more robust in the next update.
For now, I just want to see how I like the 18" A-Arms.
Testing:
- 15° Angle | 12" Ground Clearance | 58" Width
- 25° Angle | 16" Ground Clearance | 54" Width
- 35° Angle | 18" Ground Clearance | 52" Width
So it turned out that the 18" A-arm length is just a little too long. But I'm going to keep it. I figured out a way to cheat the width by making a suspension lock at 25° (54"). Just lock it and load it into the trailer like normal.
Front suspension part 2 update coming next.