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HOT ROD Suspension Tech 2008/07/08

The "S-pattern" 600-foot slalom course has become the standard for measuring a vehicle's transient response.

In my last blog we discussed skidpads, the basic tool for measuring a vehicle's steady-state cornering ability. But in the real world, cars usually don't continuously turn only in one direction. Instead, most driving involves a succession of corners, often requiring the vehicle to turn in the opposite direction from the previous corner. A slalom course has become the baseline test for what is known as "transient response," or the vehicle's ability to recover from one corner and set up for the next corner.

In competitive slalom racing no two courses are alike; they're like miniature road-race courses and are limited only to the available space and the designer's imagination. However, for engineering and magazine test purposes the standard "baseline" course configuration is simply seven cones placed in a straight line 600 feet long with each cone 100 feet apart (as shown in the diagram; click to enlarge). There is no magic to these dimensions--they simply conformed to the available room in the original parking lot when this type of testing first began back in the 1950s.

In this standard slalom, cars go through the course in an alternating left/right "S" pattern. The 100 foot cone separation distance is about equal to five average car lengths. Cars are still leaning from the previous turn before entering the succeeding turn, thereby providing the ideal evaluation of transient response. Timing begins when the car crosses the plane of the first cone and ends when the car crosses the plane of the last cone. Run-up and exit areas should be as long as possible, with entry speeds appropriate to the type of vehicle being tested (a Corvette naturally should be tested at a higher speed than a cargo van).