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