Shock technology has evolved...
Shock technology has evolved and now includes designing for control of bump rubber spring rates. There is an art and science to developing the setups we now see where on asphalt the cars run on bump rubbers on both sides and on dirt on the right front, and possibly right rear.
Once you have evaluated all of the above and feel fairly confident that the car is set up correctly, you should then work to tune the transitions into and off of the corners with the shocks. The overall work that a shock does is to resist the rebounding of the springs and control the speed of compression. Since the spring promotes rebound and resists compression as inherent properties, then the shock rate of compression control must be less than the rate of rebound control.
The amount of difference you need is directly influenced by the installed motion ratio of the spring and the spring rate. A very soft spring would need more compression rate and less rebound rate, whereas a stiff spring would need a lot of rebound rate and much less compression rate.
These are the general rules and the exception would be when running on bumpstops or bump rubbers. The spring rate of these devices is quite high, and so the shock must be designed to control that high rate with equally high rebound resistance.
Shocks affect the speed of the motion of the corners of the car and therefore the placement of loads during transitional periods. If one corner of the car is shocked stiff, then as that corner desires to move in compression, more load will be retained by that corner as well as the opposite diagonal corner of the car during the compression cycle only.
If the same stiffly shocked corner is in rebound, less of the overall load will be retained by that corner, and its diagonal corner as well, during the rebound cycle only. That is the essence of shock technology related to handling influences. Plan your shock layout by comparing the stiffness of one to the other corners and to the spring stiffness at the corner you're trying to control.
Dirt cars show a lot of travel as they negotiate the four turns. This extreme amount of wheel travel means that shocks are able to do more work than with other types of race cars.
Each corner of the car might need a different shock characteristic. The amount of difference is directly related to the installed motion ratio of the spring and the spring's rate and amount of motion.
Research on shock influences in dirt racing have shown that there are a lot of gains to be had by concentrating on your shocks. This is evidenced by the influx of new designs of shocks into the dirt car market. The age old truth is that we need to perfect our setup first before working with the shocks.
Once the setup has been balanced and the shocks are decided on, we need to evaluate the turn entry characteristics and brake bias, a very important influence in this segment of the track.
Brake bias influence can be easily determined by entering the corner with medium to heavy braking first and then entering with light braking to see if there is a difference. If there is, try to adjust the brake bias to eliminate the adverse condition.
Once you have made the entry to the corner balanced, check to see if the adjuster is centered. If it's too far to one side, then changes to the brake master cylinder sizes and/or the pad compounds might need to be made in order to maintain a centered bias adjuster. Off-centered adjusters can be very inconsistent.
Turn entry on dirt is important and dictates how well we are able to negotiate the middle of the turn. So, we need to evaluate our turn entry characteristics related to brake bias. We may want to try to solve turn entry problems with the brake bias on dirt.
More and more drivers are using braking to slow the cars on entry on dirt. We have observed top Late Model, Sprint Car and Modified drivers who win a high percentage of the races they enter, entering the turns straight ahead and braking to slow the car.