Monthly Archives: February 2013

BRZ/FR-S/GT86 Rear Lower Control Arm Design

There are two major problems with the OEM rear lower control arm on the BRZ/FR-S/GT86:
1. It doesn’t offer any camber adjustment
2. It is very weak under longitudinal loading

OEM LCA

Originally, I was going to try a shim stack design for the rear lower control arm.  However, I was unsatisfied with the design because it would either be too heavy or too soft.  So, I went back to the drawing board and started from scratch.  This time I went with a threaded rod adjustment rather than shim stacks because the shims were adding too much mass.  This is the design:

LCA V4

With a threaded rod design, we were able to reduce the mass of the arm while increasing stiffness. Here you can see the stress plot side-by-side.  The OEM arm:

OEM Stress

Note how twisted the arm becomes where the arm tapers.  Under extreme loading, the arm is likely to break at the welds.  Our arm:

LCA V4 Stress

Our FEA results show that stress is reduced in the arm by 900%, and stiffness is increased by 1100% while maintaining the same mass.

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BRZ/FR-S/GT86 Rear Toe Link

How hard could it be to design a toe link?  Not very if you just want something to “get the job done.”  However, we believe in being thorough, so we have spent nearly a hundred hours thinking through all the details.  These were our design objectives:

1. It had to be adjustable.  Changing the car’s ride height changes its static toe setting.  The adjuster was also placed in a location the user can easily access at all times, because nothing is more frustrating than struggling to fit a spanner to make adjustments.  So it could work with any ride height, it was designed to fit a modular shank to adjust the ride-steer curve for any height.

2. It had to be strong.  We created a list of over twenty potential rod ends and our toe links were designed around the rod ends, which means they can handle over 7000 lbs of load without failure.

3. It had to be stiff.  While others may discuss strength-to-weight ratio in design, when it comes to suspension, the stiffness-to-weight ratio is the key to better driving feel.  By increasing the stiffness over OEM, there is less compliance in the suspension, and less compliance means more feedback for the driver.

4. It had to last.  We selected materials that would be corrosion resistant for low-maintenance.

5. It had to be light.  It needed to be lighter than OEM and every ounce was accounted for.  We ran through multiple design iterations using multiple materials to produce the lightest product that met our design requirements.

This is the rendering of our BRZ/FR-S Rear Toe Link design

Rear Toe Rod
This product was designed with the end user in mind, so the user can “set it and forget it.”  The materials were carefully chosen for maximum performance and longevity.  The assembled toe rod should weigh just under 1.5 lbs.

The toe rod and rod ends are made of aircraft grade aluminum for its stiffness-to-weight and strength-to-weight.  The shank and bump steer shims are made of stainless steel for its strength.  Even the nuts are made from stainless to ensure the part never seizes, especially important for people who live in the salt belt that daily drive their car.

Our parts are made in the US by ISO 9001 certified manufacturers to ensure quality.  We expect to receive our first prototype by the end of the month.  Stay tuned.