My front suspension is a tubular double A-Arm and uses a Wilwood ProSpindle based on Mustang II front ends, The Mustang II is a common aftermarket front end used on a variety of hot rods. This makes the componets easy to acquire and relatively inexpensive. The Wilwood spindle was my starting point for the A-Arm design as I wanted "off the shelf" components where possible. While not a true Mustang II spindle geometry, it does accept standard wheel hubs and bearings and the updgraded Wilwood brakes that I intend to use.
The front wheel track of the RT is much wider in stance than the Mustang II so using standard A-Arms would not provide the correct geometry for the suspension travel. I made this an educational section of the build so I bought some books, did tons of research and learned much about suspensions. One thing I learned right away is that suspension design is a compromise and there is no single "correct" design geometry. The balance between toe, camber and castor is based on the type of ride experience desired and constantly changes as the car accelerates, steers and bounces. Keeping the feel and experience the same throughout suspension travel is the key parameter.
Keeping this in mind I chose to purchase a suspension design software that I could use to "tune" my design to the experience I was looking for and to match the geometry of the RT. The software is called "Suspension Analyzer" from Performance Trends . I know this will be a learning experience and expect to make changes as the RT is driven and I take data on the handling parameters, but I want to start with a goal in mind and design the components as close to that goal as possible from the start.
The software starts with the basic three dimensional coordinates of the moving suspension parts; upper a-arms, lower a-arms, tie rods, shocks, springs, etc. Tire and wheel parameters are selected as well and all components can be tweaked to see the desired results as you "move" the suspension through its range of motion. All pretty cool to an engineering guy like me who wants to know how things work and how changes will alter behavior of the suspension.
After getting some basic geometry by reverse engineering some info on the T-Rex, I started to lay out the design and test the geometry. I settled on a good compromise that met my design goals. I was fortunate early on in my research to find a lower a-arm from Chris Alston's Chassisworks that was nearly identical to the dimensions I desired. I really didn't want to fabricate the a-arms from scratch and this was a nearly perfect fit. I altered my design to fit this lower a-arm and along with the Wilwood spindle I only had to fabricate the upper a-arms. As I began my search for how I was going to build the upper a-arms I stumbled upon Victory Circle Chassis and Parts who had 2011 IMCA approved modified a-arms that were also very close to what I needed geometry-wise so I ordered a couple and it was almost too good to be true - they fit perfectly! I designed the a-arm to use Heim style joints allowing easy adjustment in all three dimensions to fine tune the suspension.
Here are a couple of pictures of the front suspension as it is going together.