The goal of vehicle design is to keep all four wheels planted if possible to maximize grip, so placing all parts in the car at their lowest possible location will help lower the CG height. Placing an engine higher off the ground raises the CG, and forces larger amounts of weight to transfer when cornering, accelerating, or decelerating. The further from this ideal point, the more one end of the car acts like a pendulum, and the more difficult it is to optimize handling. Placing the CG fore or aft or left or right of this point means that weight transfers unevenly depending on which way the car is turning, and whether it is accelerating or decelerating. The ideal place for the CG is absolutely between the front and rear wheels and the left and right wheels. Maximize CG placement and vehicle balanceĬenter of gravity affects the car like a pendulum.
The first forces which come to mind are suspension mounts, but things like the battery and driver place stresses on the spaceframe structure. Load paths are defined as the forces resulting from accelerating and decelerating, in the longitudinal and lateral directions which follow the tubing from member to member. When considering placement of tubes, visualize the “load paths”, and consider using FEA (Finite Element Analysis software) to help analyze load scenarios. See our “Designing Your Own Race Car” section Consider the load pathsĪ chassis is not about “absorbing” energy, but rather about support.
It is much easier to design a tentative suspension according to the rules and good geometry, and then build the chassis to conform to suspension mounting points and springs/damper mounts. The great thing about these materials is that they don’t have a lot of strength and so the deformations that loads create can be easily seen when loads are applied. Likewise, using cardboard, paper and glue to build model monocoques can be a very rewarding and low cost learning experience as well. His recommendation is for a 1/12 scale model. Herb Adams, in his book “ Chassis Engineering” provides a whole chapter on chassis modeling using balsa and paper. Modeling a spaceframe chassis with balsa wood sticks enables you to see firsthand the differences triangulation makes to the stiffness of a chassis. Sometimes lowering the vehicle while using the same suspension pickup points will create poor handling. If the changes involve the suspension, such as lowering the vehicle, model the new suspension first.
Identifying the correct parts of the chassis structure to cut or modify is critical.Ĭonsider using scale models of the vehicle (if plastic models were made), to mockup the changes, or 3D modeling software to do the same. The structures formed by the manufacturer’s chassis designers have strong areas intended for loads and weak areas not intended to carry loads. When considering modifying a production-based chassis to mount alternate suspension, engines or drivetrain, spend time studying the unibody (newer vehicle) or ladder-frame (older vehicle) structures. In areas where tubing sees compression loads, a heavier gauge or larger diameter tubing may be better to use.Ĭhassis Design Tips (1/2) Modifying Production Chassis As tubing in tension provides higher strength than compression, a lighter gauge tubing may be used in tension loaded areas to save weight. The key aspect of spaceframe design is to identify and analyze the loads that are to be expected, and design the frame and triangulation to handle those loads in an optimized fashion. Round tubing does not butt up against other round tubes well, and therefore requires a special tube notcher to cut round shapes into it.
Square tube is easier to work with because cutting it involves straight cuts at a particular angle. Spaceframes usually use square or round tubing. The diagram also shows suspension and other mounting brackets. Returning to diagram SF1, there are numerous examples in this diagram of how open box tube structures have been triangulated to create a much more rigid chassis. The force applied to the box compresses the cross-member, potentially buckling it if the force is sufficient.