While chief engineer Carroll Smith was traveling the world at road races I was able to engineer and detail design the torsion bar/subframe system for the 1984 PPI Toyotas. The 3-stage torsion bar system used 3 bars in series ... one longer main bar, and two shorter segments. All segments could get swapped out for varying primary, secondary, and tertiary rates. Adjustable stops at each bar transition allowed tuning of where each progressive rate began in the travel. The extra-long total bar length was accommodated by running the torsion bar through the LCA pivots attaching to the anchor at the front of the control arm. Naturally, all of the T-bars were hollow for the lightest weight design! Did you know that a hollow torsion bar is one of the most weight efficient steel spring designs? A coil spring is essentially a solid torsion bar winding up in a less efficient manner. In the 1984 Toyotas the rules dictated torsion bars due to the stock configuration, but I prefer them anyway when using a steel spring due to their mass efficiency as well as the ability to place the relatively heavy steel spring mass at the very bottom of the vehicle.
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