Suspension Design

Well, it’s been another month since my last update.  Once again I don’t have anything big to show.  Just incremental progress in several different areas of the design.  First off: I have been finishing up a lot of the little details on the frame.  Things like suspension pickups, bellcrank mounts, and various gussets.  Here is where it’s at as of this morning:


Second: I am almost ready to call the suspension totally finished.  I just need to finish up the Anti-roll bars and their mounting points and add a few little details to the Bellcrank assemblies.  Here are a few pictures:



The shock assemblies are all inboard and actuated by pushrods and bellcranks.  This was done for a couple reasons.  Most obvious is the aerodynamic benefit of getting the dampers and springs out of the air flow to reduce drag.  Going along with that, all of the control arms, tie-rods, and pushrods will be made of airfoil section Streamline Tubing.

Streamline Tubing

Another benefit of the inboard suspension is that the bellcrank geometry can be set up such that the Motion Ratio increases as the suspension is compressed.  This works to increase the effective spring rate (or suspension stiffness) as the wheel travels upward relative to the chassis.  Of course, it is possible to get progressive rate springs that produce similar results but the progressive rate bellcrank has the advantage of also increasing the damping rates as the spring rates increase keeping the damper settings closely matched to the spring throughout the suspension travel.  Linear springs are also cheaper and much more commonly available in hundreds of different rates.

The last inboard suspension benefit I’d like to talk about is the ability to achieve fairly high motion ratios (even >1 if you want) by using bellcranks.  If I were to use outboard shocks on the TT1, they would be laid over so far (probably around 30 degrees from horizontal) that the highest motion ratio I could get would be around 0.5.  That means that for every inch the wheel moves, the shock only moves 0.5 inch.  It also means my Spring and Damper Rates need to be 4 times my desired wheel rates (adding weight and probably increasing cost).  It also makes the dampers less sensitive to small displacements due to small bumps and dips since the shock only sees half of the movement the wheel sees.

I ended up with front and rear Motion Ratios starting at around 0.85 at full droop, increasing to .92 at nominal ride height, and topping out at 1.05 at full bump.  I’m not sure if that will be too progressive or not progressive enough, but it would not take much work to machine new bellcranks with slightly different geometry to experiment with if I need to.

Okay, enough about suspension.  I have also made a bit more progress on the bodywork design.  I’m fairly happy with the direction most of it is going but I haven’t come up with a design for the nose that I like yet.




Oh, and an engine arrived last week.  I need to take off the parts I won’t be using (Intake and Exhaust Manifolds, A/C Compressor, Power Steering Pump, etc.) and get it modeled up to make sure it’s going to fit in the frame.  Then I can start on designing the motor mounts and the engine / transmission adapter plate.  It’s slow going but I am hoping to be able to start building the frame within the next couple months.  Thanks for reading.

  • Mickey Oswald

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