Suspension

Suspension in Frame

Features


Minimum bump-steer design
7075 Aluminum adjustable bell cranks in front and rear
Reverse thread adjustable A-arms
Pushrod-style actuation
Non-invasive front suspension design allows more legroom
5/16” ball joint inserts for strong connections

 

Rule Analysis

Rule #

Rule

Analysis

4.2.1-3

A free vertical cross section, which allows the template shown in Figure 9 (See Formula SAE Rules) to be passed horizontally through the cockpit to a point 4 in. rearwards of the face of the rearmost pedal when in the inoperative position, must be maintained over its entire length.
The only things that may encroach on this area are the steering wheel, steering column and any padding that is required by Rule 5.7 "Driver's Leg Protection."
For 2009, teams whose cars do not comply with 4.1 or 4.2 will have 35 points deducted from their Design Event score.

This is one of the main challenges facing the 08-09 design team. This rule forced us to move our front hoop bracing and clear the area over the driver's legs. In order to meet clearance requirements, the coilovers will run along the length of the body, rather than meeting at its center. Great care must be taken to ensure that the springs, bell cranks, and all their shielding are wide enough to permit passage of the template in Figure 9.

5.7.1

To keep the driver's legs away from moving or sharp components, all moving suspension and steering components, and other sharp edges inside the cockpit between the front roll hoop and a vertical plane 4 in. rearward of the pedals, must be shielded with a shield made of a solid material. Moving components include, but are not limited to springs, shock absorbers, rocker arms, anti-roll/sway bars, steering racks and steering column CV joints.

Placement of the front suspension members (esp. coilovers and anti-roll/sway bars) must be covered.  Therefore we must leave ample space for the protective shielding when considering placement for these members.  Designing with the template in Figure 9 in mind will be imperative.

5.7.2

Covers over suspension and steering components must be removable to allow inspection of the mounting points.

Expendable zip ties or screws may be suitable for this requirement.

6.1.1

The car must be equipped with a fully operational suspension system with shock absorbers, front and rear, with useable wheel travel of at least 2 in. (1 in. jounce and 1 in. rebound), with the driver seated. Judges reserve the right to disqualify cars which do not represent a serious attempt at an operational suspension system or which demonstrate handling inappropriate for an autocross circuit.

The formula car is already equipped with a suspension that meets these standards. Our goal will be to improve the design without losing performance.  A good math model and some drive time will be necessary to verify compliance with this rule.

6.1.2

All suspension mounting points must be visible at Technical Inspection, either by direct view or by removing any covers.

Body shell must be easily removable or mobile.

6.2

The ground clearance must be sufficient to prevent any portion of the car (other than tires) from touching the ground during track events, and with the driver aboard there must be a minimum of 1 in. of static ground clearance under the complete car at all times.

Because much of our geometry is staying the same and the car currently has much more than 1 in. of clearance, this is not a large concern.

 

 

Suspension Parameters
Front
Rear
Suspension Type Double unequal length, non-parallel A-arm. Bell crank actuated spring and damper w/pushrods. Double unequal length, non-parallel A-arm. Bell crank actuated spring and damper w/pushrods.
Tire Size and Compound Type 20x7-13 R-25A (Dry) 20x6.5-13 (Wet) 20x7-13 R-25A (Dry) 20x6.5-13 (Wet)
Wheels 7 inch x 13 inch Al Billet 7 inch x 13 inch Al Billet
Design ride height (chassis to ground) 4.5 in 4.5 in
Center of Gravity Design Height 12.00 in above ground
Suspension design travel 1.63 in jounce/1.16 in rebound 1.4 in jounce/1.1 in rebound
Wheelrate (chassis to wheel center) 149 lb/in 213 lb/in
Roll rate (chassis to wheel center) 0.65 deg/g
Sprung mass natural frequency 3.5 Hz 3.8 Hz
Jounce Damping 98% of critical damping at 2 in/sec 75% of critical damping at 2 in/sec
Rebound Damping 98% of critical damping at 2 in/sec 75% of critical damping at 2 in/sec
Motion ratio 0.93/linear 1.12/linear
Camber coefficient in bump (deg/in) 1.07 deg/in 1.13 deg/in
Camber coefficient in roll (deg/deg) 0.5 deg/deg 0.28 deg/deg
Static Toe and adjustment method 0", adjustable via steering rod 0", adjustable via adjustable tie rod
Static Camber and adjustment method -3 deg, adjustable via adjustable upper a-arm -3 deg, adjustable via adjustable upper a-arm
Front Caster and adjustment method 6 deg, adjustable via adjustable upper a-arm  
Front Kingpin Axis 3 deg  
Kingpin offset and trail 1.25 in offset, 0.85 in trail  
Static Ackerman and adjustment method 45% at max steer angle, non-adjustable  
Antidive/Anti-Squat 0% 0%
Roll center position static 1.9 in above ground 1.98 in above ground
Roll center position at 1g later acc 1.702 in above ground, 1.404 in toward unladen side 1.792 in above ground, 1.09 in toward unladen side
Steer location, Gear ratio, Steer Arm Length Front steer, 4.25"/revolution, 3.19 in steer arm

 

Detailed Design