Until the advent of the suspension cam on ESPN’s NASCAR Winston Cup coverage, suspension springs were almost entirely ignored by racing fans. For that matter, many racers are surprisingly uninterested in the actual specifications and quality of their springs, let alone the details of their design and manufacture. This seems a pity, For reasons of both convenience and operational efficiency, the vast majority of racing cars are suspended by coil springs-and the quality of the springs is crucial to the car’s speed, driveability, and consistency.
In addition to keeping the chassis off the track, race car suspension springs serve the same basic purposes as passenger car springs. The springs isolate the components (and the occupants) of the vehicle from road shock. They control the pitch and roll attitudes of the vehicle and, in concert with the shock absorbers, the rate at which these attitudes change in response to the forces of lateral, longitudinal, and vertical acceleration. Finally, again with the shocks, they keep the tires in contact with the road surface as constantly as possible. Actually, shock absorbers do not absorb road shocks the springs do. The shocks control the release of the energy stored in the springs when they are compressed. In the world of passenger cars, even high-performance passenger cars, production-quality coil springs fulfill these functions satisfactorily. Racing imposes more stringent requirements, which include better accuracy of manufacture, minimum practical size (where rules allow variability-Winston Cup does not), and weight, along with absolute consistency of performance. A passenger-car spring that is a bit off in rate, free length, or in load at a given height-or that takes a small set or a slight sag in extended service-won’t make a significant difference to the driver in performance or response. Not so in racing.
In racing, more than in most fields, time and money are interchangeable. We never have enough of either. We simply cannot afford the time to fuss around with any component that is not the very best of its type. No one argues with this point when it comes to the high-profile items: valves, crankshafts, connecting rods, rod bolts, ignition systems, shock absorbers, and so on. It is equally true of suspension springs. There are a couple of reasons.
First, both ride height and corner weight are functions of the load at height of the individual springs at each corner of the car (not, as is often supposed, of either the rate or the free length of the springs). If one or more of the springs sags or takes a set in use, the height at load- of the spring, the corner weights, and the ride heights of the car will change accordingly and the balance of the car will change with it. The change is seldom for the better.
We often hear a driver report that his race car either got loose or developed a push during a race. This is usually blamed either on changing track conditions or on a particular set of tires. The real culprit could well be sagging suspension springs.
Think about it. A Winston Cup Car on a super-speedway will be running a dynamic ride height so low that the frame can bounce off the track, sparking as it rolls along at, for example, a buck eighty-five at Charlotte. An IRL or CART car on a big oval will be running a dynamic ride height of less than X` with spring rates in the 2,500-5,000 lbs./in. range. One spring taking a very small set can alter corner weights enough to turn a perfectly balanced race car into an undriveable pig. The situation in stock cars (and in road racing) is less critical but only slightly so. Chasing this sort of thing wastes time, effort, tires, and engines and can drive sane crews mad.
But it doesn’t end there. During practice and testing, race teams change springs frequently. Every time they do, the car should go back on the alignment level pad and the ride heights and corner weights should be reset. But teams don’t have time for that. Have you watched a happy-hour show on TV lately? Everyone is in a thrash.
The closer to perfection the springs are, the less the margin for error and the less irretrievable practice time is lost.
Racing’s rapid growth has played an important part in the expansion of the racing-spring market. But the largest factor in the greatly increased demand for better-quality and more consistent racing springs has been fostered by the increasing sophistication, in all forms of racing, of racing shock absorbers. This sophistication is the result of fierce competition . At a recent Winston Cup race, 38 cars qualified within 0.3 seconds of the pole. As racing gets more competitive, engineers and crew chiefs are focusing more attention on optimum suspension performance and consistency in the search for the last Xoo or even Xo. of a second.The racing representatives of the high-tech shock manufacturers-Bilstein, Dynamic, Koni, Ohlins, and Penske-are teaching grassroots racers what the tip of the racing iceberg has known for decades. To realize the performance benefits offered by sophisticated shock absorbers, the springs must be absolutely consistent in load at height, rate, and linearity.
Reprinted from Stock Car Racing Magazine, 277 Park Avenue, New York, NY 10172 © General Media Automotive Group, Inc. 1998