Introduction to Formula SAE® Suspension and Frame Design
Edmund F. Gaffney III and Anthony R. Salinas
University of Missouri - Rolla
ABSTRACT This paper is an introduction to Formula SAE® (FSAE) suspension and frame design based on the experience of the design team at UM-Rolla. The basic theories and methodologies for designing these systems are presented so that new teams will have a baseline for their first FSAE design. Examples will be given based on UM-Rolla’s 1996 FSAE entry. INTRODUCTION Formula SAE® is a student competition, sponsored by the Society of Automotive Engineers (SAE), in which students design, build, and compete with a small formula style race car. The basis of the competition is that a fictitious company has contracted a group of engineers to build a small formula car. Since the car is intended for the weekend autocross racer, the company has set a maximum cost of $8,500. The competition rules limits the race car engine to a maximum displacement of 610cc with a single inlet restrictor. Other rules require that the car must have a suspension system with a minimum wheel travel of 50mm and a wheelbase greater than 1524mm. The car must also satisfy safety requirements such as side impact protection . The competition is separated into static and dynamic events. The static events include the cost analysis, sales presentation, and engineering design. The dynamic portions of the competition are the 15.25 m diameter skid-pad, 91.44 m acceleration event, 0.8 km autocross, 44 km endurance race, and fuel economy. The FSAE competition was established to provide an educational experience for college students that is analogous to the type of projects they will face in the work force. To participate in FSAE, student groups work with a project from the abstract design phase until it is completed. Aspects of engineering design, team work, project management, and finance have been incorporated into the basic rules of 1
Formula SAE®. This paper covers some of the basic concepts of suspension and frame design and also highlights the approach UM-Rolla used when designing its 1996 suspension and frame. The suspension section addresses the basic design parameters and presents specific examples. The frame section discusses how to achieve a compromise with the FSAE design constraints. Finally, the design section gives a brief overview of the design methodology used by UM-Rolla for the 1996 race car. The 1996 team finished 12th in the engineering design event, while the overall finish was 19th out of 77 competing teams. 1 SUSPENSION GEOMETRY
The suspension geometry section concentrates on some of the basic areas of suspension design and highlights what the UM-Rolla design team selected for its 1996 race car suspension geometry. FSAE suspensions operate in a narrow realm of vehicle dynamics mainly due to the limited cornering speeds which are governed by the racetrack size. Therefore, FSAE suspension design should focus on the constraints of the competition. For example, vehicle track width and wheelbase are factors governing the success of the car’s handling characteristics. These two dimensions not only influence weight transfer, but they also affect the turning radius. Not only does the geometry have to be considered for FSAE suspension, but the components must also be reasonably priced for the cost analysis and marketable for the sales presentation. For example, inboard suspension could be a more marketable design, while outboard suspension might cost less and be easier to manufacture. UM-Rolla chose to use a four wheel independent suspension system with push rod actuated inboard coil-over
shocks. This decision was mainly due to packaging constraints. Furthermore, the appearance of inboard suspension was considered important for both the design judging and the sales presentation because of its similarity to modern race cars. Although this discussion is of short-long arm suspension systems, many of...