1. Suspension
D.J. Conroy

2. Last year Designed with existing frame
Did not use suspension analysis programming
A-arms not easily adjustable
Hard to assemble

3. This year Design frame around suspension
Find optimum geometry using Lotus
Make adjustment, machining, and assembly much easier

4. Geometry Analyzed using lotus software
Mounting points dictate much of the frame layout

5. Different Set-ups

6. Most Important Aspects
Castor
Camber
Toe
Roll center height

7. Optimum Settings -1° camber (static) Front toe 5° of castor
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
Roll center height of about 2 in
Stay positive through bump/droop
Converging A-arms

8. Mounting lower than 6in. (2in. shown)

9. 6in. pentagon

13. Pentagon Specs: 1° roll: 6.5° Roll Center: Toe: Static: 0.8in
1 in bump: -1in
1 in bump: -12°
1in droop: 0.7in
1in droop: 14.5°
Camber:
1° roll: 6.5°
Static: -1°
1 in bump: -2.05°
1in droop: -0.25°

14. 6in. octagon

18. Frame sketch

19. Octagon Specs: 1° roll: + 2.5° Roll Center: Toe: Static: 2.7in
1 in bump: 1in
1 in bump: -5°
1in droop: 4in
1in droop: 7°
Camber:
1° roll: + 2.5°
Static: -1°
1 in bump: -2.2°
1in droop: .1°

20. Octagon vs. Pentagon Advantages: Disadvantages:
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

21. 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.

22. A arm Dimensions Upper: Lower: 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°

23. Materials Steel Carbon Fiber Good: Bad: Easy to weld Light weight
Cheap
Bad:
Expensive
Heavy
Hard to bond to steel

24. 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

25. Adjustability
Exposed outer rod end:

26. Forces on Wheel

27. A-Arm Forces

28. Breaking: Verticle: Lateral: tyre: 217.7 lb Top arm: 114.3 lb
Bottom arm: 332 lb
Verticle:
tyre: lb
Top arm: 290 lb
Bottom arm: 290lb
Lateral:
Tyre: lb
Top arm: lb
Bottom arm: lb