Suspension - Part 2 - Ride and Handling

Measuring Handling

There are several ways to test handling, some more subjective than others. One of these tests, the skidpad, is a great place to measure ultimate “steady state” cornering ability. It’s a simple test, where you drive around a pre-measured circle at the very limits of traction. By steady state, we mean that we try to keep the conditions of the test constant, by keeping the throttle and steering wheel as steady as possible while trying to stay centered on the prescribed circle. Based on your elapsed time for one lap around the circle (with a running start), the lateral acceleration of the car can be determined. This quantity is expressed in terms of acceleration due to gravity, or “g”. One “g”, (1.0g) which is a benchmark of sorts, means that the car generates sideways grip that is equivalent to the weight of the car. I like to describe 1.0g by noting that if you were turning right at 1.0g with no seatbelt, the force pushing you against the driver side door would be enough to hold you up if the seat were removed from underneath you. Kind of like the amusement park ride that spins you around in a big drum and then drops the floor out from under you, leaving you pinned to the wall with no visible means of support.

Another test is the slalom, where cones are spaced at even intervals in a straight line. This is a great test of a car’s “transient” handling ability. By transient handling, we mean the ability of the car to transition, or change direction, in a controlled manner. The driver enters the slalom (again with a running start) and weaves back and forth through the cones as fast as possible without hitting cones or losing control, the time from the beginning to the end of the cones is measured, and an average mile per hour speed is determined.

A third test would be comparative lap times around a racetrack or other controlled course, which would create a combination of both steady state and transient handling conditions. The trick to getting good results in any of these tests, of course, is to have an experienced, consistent driver, otherwise, the results could be less than optimal.

Measuring Ride

Ride, being a more “subjective” subject, is a little more difficult to define, and each individual has his own perceptions. There are actually calculations that can be made, based on the weight of the car, the spring rates, and the shock absorber characteristics. The results of these calculations are compared to many years of data gathered by car manufacturers and testing facilities about what most people find to be comfortable or harsh. The most common calculation used to analyze ride is what’s referred to as ride frequency, which is actually a simple calculation that looks at the relationship between the spring rate and the vehicle weight. Ride frequency is usually expressed in terms of cycles per second (commonly known as Hertz, abbreviated Hz). If you have ever checked your shock absorbers using the “push down on the bumper and see if the car goes down and up more than once” test, you've taken a rudimentary step toward measuring your ride frequency. If the shocks are completely worn out, and the bumper goes up and down several times, it will do so at the ride frequency. This number is usually calculated mathematically, though, to eliminate other influencing factors.

While ride may be a personal preference issue, much has gone into the study of how the human body reacts to various inputs – certain parts of your body actually vibrate in harmony with certain frequencies that a car chassis can produce, sometimes with uncomfortable results. If you’ve ever been to a live concert and been close enough to the sound system that you really feel the music as much as you hear it, especially the heavy low notes that sometimes make your chest feel like it’s vibrating, you are experiencing the same kind of thing I’m talking about.