Testing, Testing 1,2 ...

[DougMilliken]

Have you seen this presentation I had Pat post on the Facebook FSAE site ?

Thanks Bill, those are great slides. In my FSAE lecture I try to cover some of the same ground. After an overview of tire force and moment properties, applying the tire data to a vehicle model requires operating conditions--what is the load on each tire and where are the tires pointing. That is where K&C comes in because it's not at all obvious how a suspension is going to deflect in operation.

I strongly recommend that anyone planning to use K&C data witness a test in person. There is a lot going on during the test and there are many detail differences from one rig to the next--some machines (ABD, MTS, original Chevrolet VHF) are comprehensive, others test piece-wise and may not cover every combination of loads and deflections.

For example, John Ellis* built an early rig which applied horizontal force to move a vertical axis pivot laterally, this pivot supported a pad under the tire contact patch. To apply varying amounts of aligning torque resulting from the applied force, he would move the pivot point (and wheel pad) away from the contact patch center. Of course this meant that he wasn't applying a pure moment (the way it's commonly done now). From memory he developed a clever way to separate the two effects(?) and his machine was much lower cost to build. *https://www.worldcat.org/title/vehic...oclc/655191086

At the Chrysler Proving Ground, they used to have two separate axle testing rigs, one capable of heave & roll for kinematics, the other for compliances.

Before designing their SPMM, ABD used their 4-post ride rig with additional fixturing/actuation to measure partial K&C properties for their customers.

Lotus built their own low cost rig in house, it took multiple setups to apply forces in different directions. They may have sold some copies (not sure).

The history goes back a good ways. Maurice Olley at GM had a clue. Here's a short quote from our book, "Chassis Design" which is based on his notes from the early 1960s,
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3.7 Lateral Deflection Steer

In addition to the changes in the pointing of the wheels (relative to the median plane) due to the roll of the car, there are sometimes appreciable changes due to deflections in the suspension mechanism under lateral forces. These have been less thoroughly studied than roll steer effects, partly because they are more difficult to measure accurately.

Probably the only realistic way of measuring them is by instrumentation on the road. However static shop tests give clear indications that lateral deflection steering effects exist. Their importance became apparent with increasing use of rubber bushings.
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-- Doug Milliken