Suspension D.J. Conroy
Suspension
D.J. Conroy
Last year
• Designed with existing frame
• Did not use suspension analysis programming
• A-arms not easily adjustable
• Hard to assemble
This year
• Design frame around suspension
• Find optimum geometry using Lotus
• Make adjustment, machining, and assembly much easier
Geometry
• Analyzed using lotus software• Mounting points dictate much of the frame
layout
DifferentSet-ups
Most Important Aspects• Castor
• Toe
• Camber
• Roll center height
Optimum Settings• -1° camber (static)– 1° change per inch bump/droop
• Front toe– -1° toe in static (positive with lotus sign convention)– Minimal change in bump/droop
• 5° of castor– Minimal change in bump/droop
• Roll center height of about 2 in– Stay positive through bump/droop
• Converging A-arms
Mounting lower than 6in. (2in. shown)
6in. pentagon
Pentagon Specs:
6in. octagon
Frame sketch
Octagon Specs:
Octagon vs. Pentagon
• Advantages:– Lower and shorter (from bottom to top of frame)– Lower COG– Don’t need to worry about a raised front end– Better mounting of steering rack• Much less bump steer
• Disadvantages:– Heavier– More frame members
My opinion:
• The couple extra frame members and 5 lbs max additional un-sprung weight is worth it to have a much lower center of gravity and much less bump steer.
A arm Dimensions • Upper:– Forward arm 15.08in– Trailing arm 14.70in– Difference: .38in– Angle: 51.7°
• Lower:– Forward arm: 15.73in– Trailing arm: 16.09in– Difference: .36in– Angle: 48.2°
Materials
Manufacturing and Assembly
• Rod ends with built in spacers• Mill push rod mounts• Use steel or carbon fiber rods• Jig:– Accurate – 3 points– Could use mill table
Adjustability
• Exposed outer rod end:
Forces on Wheel
A-Arm Forces
• Breaking:– tyre: 217.7 lb– Top arm: 114.3 lb– Bottom arm: 332 lb
• Verticle:– tyre: 580.6 lb– Top arm: 290 lb– Bottom arm: 290lb
• Lateral: – Tyre: 290.3 lb– Top arm: 152.4 lb– Bottom arm: 442.7 lb