Suspension (23-24)

This will be an overview of everything I worked on during my time as suspension lead from 2023-2024. My projects during 2021-2023 is a separate section as it would be too much to put all on one page. If you'd like more information, please contact me!

Background Info

Using the info I learned from the 2022-2023 car, the 2023-2024 car builds on a solid foundation using the same 16x7.5-10 R20 tires, similar kinematics with small tweaks, and lots of setup changes based on the vehicle dynamics tool I made as well as testing.

Toe change

In my suspension (21-23) page I mention a flaw I discovered while mounting the inside tab for rear the tie rod. This flaw is the sensitivity of the global placement of the inside rear tie rod point.

Instant center diagram

In order for there to be zero toe change, the axis of the tie rod must intersect with the instant center. Because of this, any tolerance in mounting of the inner tie rod tab will cause the actual toe change of the vehicle to be different than the calculated toe change. Due to the geometry of the chassis, it was very easy for there to be tolerance stack up during the drilling of the holes for the tab.

Designed toe change graph in bump

Inner tie rod point moved down 0.050"

As you can see from the graphs above, changing the inside tie rod point location has a huge effect on the toe change of the rear suspension.

To eliminate this possibility of tolerance stack up, I mounted the tie rod on the same plane in front view as the upper A-arm. This keeps the tie rod at the exact same angle as the upper A-arm at all times, keeping the bump steer at zero.

Rear Damper Packaging

For the 2023-2024 car we decided we wanted to run a larger rear sprocket for a shorter gear ratio. Because of this the rear damper configuration needed to be changed as the sprocket would have gone right through the damper.

Due to time constraints, we could not change the chassis design. To work around this, about the only other option for damper configuration was pull rod. The pull rod configuration packaged very nicely, keeping a 1:1 motion ratio for easy tuning, easy adjustment, and serviceability.

2023-2024 Damper configuration

Stress Analysis

The prior method of determining load cases was very crude napkin math. In order to design all components of the suspension to meet the load cases the vehicle sees I made a spreadsheet based on an article on FSAE wiki to calculate the load in each link based on lateral and longitudinal accelerations.