If, for example, a "3" shock or an "A" shock were rated by each manufacturer at 100 pounds of resistance, comparing them would depend on what speed of movement each company rated that 100 pounds. We know the rate of resistance is directly related to shaft speed. Company X might rate the 100 pounds at 5 inches per second of shaft speed where company Y might rate the 100 pounds at 10 inches of shaft speed. We can see where the two would not feel the same to the driver. The X shock might well be 150 pounds of resistance at 10 inches per second of shaft movement where as the Y shock might be only 75 pounds of resistance at 5 inches per second of shaft movement.
To simplify things, we will use the numbering system to relate to the amount of rebound and compression, the smaller number representing less resistance. Because we are not telling the exact rate in pounds of resistance for each number, the comparisons and trends will be good for either a dirt or asphalt stock car. Generally speaking, dirt cars require a softer overall package than asphalt cars.
A basic starting shock setup for a medium-banked race track might be a pair of "six" shocks on the front and a pair of "five" shocks on the rear. These would be true 50/50 shocks where the resistance in either direction, rebound or compression, would be equal. If the shocks were the split-valve design, each shock would be numbered as say a 6/5, which for our purpose means that the first number will represent the rebound resistance and the second number will represent the compression resistance.
Controlling wheel movement would be much easier if the shocks were all we had to work with. But in reality, our race cars are supported by a set of springs. If we wanted true equal resistance to wheel movement with the shocks installed along with the springs, we would want the rebound resistance to be greater than the compression resistance (reference Part One - July, 2003 issue - where we said that springs promote rebound and help provide resistance to compression). As we install stiffer springs, we will naturally increase the rebound resistance and decrease the compression resistance.
When a shock is run on a dyno, it is cycled at different speeds and theresistance is accurately measured by load cells. It is important to gothrough this process to know the true rating of each shock, and toinsure that every part is working properly. All shocks should beinspected, rebuilt and dyno'd at least once a year.
The more balanced shock layout might look like this: Front shocks = 6/5, rear shocks = 5/4. The greater rebound helps control the force of the preload on the spring as it is released and the softer compression works along with the resistance to compression provided by the spring.
High-Banked Setups
For a setup that uses higher-rated springs in the front and rear for a higher-banked race track, we might use a pair of 6.5/4.5 shocks on the front and a pair of 5.5/3.5 shocks on the rear. That is because the higher rating in the springs promotes rebound and therefore we increased the rebound resistance. The higher spring rates also resist compression and so we can reduce compression resistance in the shocks.
When the banking of the race track is very high, say 18 degrees or more, we need split valving, but we would go up on both the rebound and compression rather than up on rebound and down on compression. The reason is that the turn speeds are much higher on the very high-banked tracks and the shocks will move much faster in both the transitional areas of entry and exit, and also as the car goes over bumps and dips in the race track. Without the higher level of control, the suspension might bottom out with obvious negative results.