Years ago, when stock car racers needed shocks, they went to the local auto parts store, bought a set of heavy-duty passenger car shocks, and bolted them on. It was even a common practice to use pairs of shocks at each corner of the car for increased dampening. And back then, the only shock testing that racers did was to stroke the shocks in and out by hand and see how they felt.

Recognizing that passenger car shocks were far from ideal for racing applications, industry pioneers such as Carrera's Dick Anderson began producing shock absorbers specifically for race cars. Soon there were numerous companies producing racing shock absorbers. Like Carrera, some manufacturers were new companies concentrating solely on racing applications, while others such as Koni and Bilstein were already established OEM manufacturers. Racers soon had hundreds of different part numbers to choose from.

For the most part, however, racers still relied on simple hand stroking to evaluate the stiffness of their shocks. While this simple test can detect a totally worn-out passenger car shock, it offers no information about how the shocks will perform under high-speed racing conditions.

That did not escape the attention of the shock manufacturers. They knew they needed to test the performance of their shocks at much higher piston speeds than were possible by hand. That led to the development of shock dynamometers.

Early shock dynos were purely mechanical devices that stroked the shock at various speeds and recorded the forces required with moving pen plotters. More recently, shock dynos have become computer-controlled, and in some cases they can be programmed to emulate the on-track motions recorded by an in-car data-acquisition system.

While shock dynos were becoming more sophisticated, the effects on handling of different shock absorber dampening forces were becoming better understood - especially the forces that shocks produce at low piston speeds, such as those that occur while a car is rolling. This understanding led to a proliferation of shock dynos and dedicated shock engineers among high-dollar race teams everywhere.

Today, there are perhaps a dozen companies that manufacture shock dynos for sale directly to race teams. These laboratory-quality shock-testing machines typically start at over $6,000 and can cost well over $100,000 for more sophisticated models. As with engine dynos, high prices have kept shock dynos beyond the reach of most racers.

There are at least two companies, however, that are trying to change that by offering less expensive shock dynos built especially for low-budget race teams. These two manufacturers have taken different approaches to designing their shock dynos; each has its own advantages and disadvantages.

GOING IN CYCLES: The Brinn shock dyno uses a 2 HP electric motor to cycle the shock through alternating compression and extension motions while a load cell measures the peak shock forces in each direction.

Herb Brinn is best known for his patented two-speed racing transmissions with their internal clutches, but he also manufactures shock dynos - including the relatively inexpensive model shown here.

This machine is basically a bare-bones version of those that cost more than twice as much. It uses a bell crank driven by a two-horsepower electric motor to cycle the shock through bump and rebound. The bell crank has two shock mounting holes at different radial distances. Bolting the shock to the inner hole cycles the shock at a low peak speed of 4.7" per second, while mounting the shock in the outer hole cycles it at a peak speed of 13.3" per second. This allows shock data to be collected at a low piston speed and a moderately high piston speed.

As the electric motor rapidly cycles the shock through bump and rebound, a precision load cell connected to the other end of the shock continuously measures the varying compression and extension forces that it produces. The peaks of these two forces are then displayed on two digital readouts - one for compression and one for rebound.

We found that by cycling a shock at the high-speed setting for a couple of minutes, it became hot enough to fry spit. It also had significantly different dampening characteristics at that elevated temperature. The same thing can happen to the shocks on a car during a race. Testing your shocks at different temperatures can provide valuable data, especially if you know at what temperature your shocks operate under racing conditions.

CRANKING: As is the case with most shock dynos, a bell crank assembly is used to produce the required stroking motions. Moving the shock mount between two different holes in the crank changes the peak speed of the shock.

This 160-pound bench-top machine is built around a rigid welded-steel frame and will run on either 110 or 220 volts, single-phase power. We found it quick and easy to set up and use. It provided highly repeatable data at two shock piston speeds within less than a minute of testing time. It has a base price of $3,289 as shown, and a similar model that includes a continuously variable stroking speed control is also available at a substantially higher cost.

ND Tech's Leo Anderson has designed a shock dyno that uses a totally different testing technique. Rather than cycling the shock at predetermined speeds and measuring the forces that it produces, his dyno exerts a series of known forces on a shock and then measures how fast it moves. In a sense, this is the opposite approach taken by most shock dyno manufacturers, but it can provide exactly the same data.

This machine is powered by compressed air passing through a precision pressure regulator and a control valve, and then into a two-inch diameter air cylinder. The shock is secured to the dyno's frame at one end and to the air cylinder's piston rod at the other. When the compressed air enters the air cylinder, it produces a force that either compresses or extends the shock. Since the force acting on the shock is directly proportional to the set air pressure, accurately timing the motion of the shock (in seconds) over a known distance (in inches) will allow its velocity to be computed (in inches per second).

Using low air pressures will stroke the shock at low speeds, while higher air pressures will stroke it at higher speeds. By repeating this test in both compression and extension for a series of different air pressures, the shock's forces can be measured over its entire range of operating speeds.

At first it might seem time-consuming to test the shock at a series of different air pressures, but it actually goes quite quickly. I spent about as much time recording the results as I spent performing each test.

To expedite the data-collection process, Anderson supplies a handy notepad with a chart printed on each page. He also supplies a simple-to-use computer program for recording and plotting the data. I have been told that many of his customers just use the notepad to record their individual shocks' data, and that they do not bother plotting it. To be sure, the data points are all that is necessary to compare different shocks or to see if a given shock has changed its dampening forces over time.

While it is true that it takes a little longer to use ND Tech's shock dyno than to use a computer-controlled dyno, there is a big difference in cost. ND Tech's dyno (model E-5 as shown here) lists for $1,695, completely assembled and powder-coated. In addition, a kit is also available that includes all the required components. At $795, these kits are great for the DIY racer on a limited budget.

SOURCE

Brinn Incorporated
1615 Tech Drive
Bay City, MI 48706
989-686-8920