In today's racing world, we have pre-built shocks available with any number of combinations of disk designs and valving. Some types of designs provide the ability to adjust shock rates quickly at the race track. With all of these choices, we have what we need to choose the exact rate of compression and rebound necessary for a particular set of conditions. This can either be an advantage or the proverbial "enough rope to hang..." syndrome. The more we learn, the better we can make decisions regarding shock selection.
Performance gains are possible...
Performance gains are possible by knowing how shocks will affect chassis movement and weight transfer. It is important to know our shock rates and how different rates produce desired effects. Proper shock mainten-ance helps us to be sure that parts are working and our shock rates have not changed.
More and more, racers are being educated in all aspects of chassis tuning and they want to know more about shock technology. The more we know about each of these subjects, the less fear we have. It is what we don't know that we fear the most.
The information presented here is intended as a guide to help you understand the basic principles of shock technology and the art of track tuning with shocks. Exact rates for the shocks you need for your car will depend on how your car is constructed, set up, and driven, as well as factors such as weight distribution and race track characteristics.
We would really like to give you the exact shock values that will make your car as fast as it can be, but that would be impossible due to the many variables. Those variables are why you must work with your particular car and not follow what others are doing. Each car is a little different than the others and each driver has his/her own style of driving.
Part One dealt with the basic construction of the racing shock. We learned that the two strokes of the shock, rebound and compression, are looked at separately and perform functions related to different areas of track tuning. If we deal with rebound and compression separately, we need to be able to tune each independently. There are also different designs of shock pistons including the linear design and the digressive design. Again, we are able to achieve varying results by utilizing all of the variables of shock design.
When a shock is run on a dyno,...
When a shock is run on a dyno, it is cycled at different speeds and the resistance is accurately measured by load cells. It is important to go through this process to know the true rating of each shock, and to insure that every part is working properly. All shocks should be inspected, rebuilt and dyno'd at least once a year.
For some situations, we would use split valve shocks. Split-valving means we have different rates of resistance for rebound and compression because we need to tune each movement a little differently than the other. We can also rate the two movements differently for each corner of the car to further tune the setup. If we want, we can buy (at a greater expense) shocks that have external adjustments for rebound, compression, or both (called double adjustable). That way, we can experiment with different shock rates without removing them from the car. Regardless of how we arrive at different shock rates, we do need to know beforehand what we are looking for and how to get there.
Shock companies provide a system of numbers or letters to reference the rates of rebound and compression. Most of these companies try to provide a cross-reference so that their numbering system can be compared to the other systems used by competing shock brands. The ultimate match between shock brands is not exact due to differences in design of the valving and the fact that companies will rate shocks at a different shaft speed.
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 shock that moves in direct...
A shock that moves in direct proportion to the spring moves at the exact same speed as the spring. This is especially true with the coilover design. On some designs, the shocks and springs are mounted at different distances from the ball joint and move at different speeds in relation to the wheel speeds.
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.
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.