This dirt car has the battery...
This dirt car has the battery mounted high and just to the left of the center of the car just in front of the rear end. A high center of gravity helps provide more load transfer on dry, slick tracks. This promotes better side bite and quicker turn speeds.
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. 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.
Shocks affect the motion of the corners of the car and therefore the placement of wheel loads during transitional periods, and dirt cars are almost always in transition. If one corner of the car is shocked stiffer, as that corner desires to move in compression, more load will be retained by the tire on that corner as well as the opposite diagonal corner of the car during the compression cycle only.
If the same stiffly shocked corner is put in rebound, some load will be lost by that corner, as well as its diagonal corner, during the rebound cycle only. That's the essence of basic shock technology related to handling influences. A coilover shock mounted on a swing arm will move less than the chassis and therefore would need to be rated higher than if it were mounted to the axle or birdcage.
7. Brake Bias 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.
Brake-bias influence can easily be determined for any race car by entering the corner with medium to heavy braking first, then entering with light braking to see if there is a difference in the car's attitude. If there is, try to adjust the brake bias to improve the entry conditions under heavy braking to what it is under light braking.
With the pull bar third link,...
With the pull bar third link, you can usually mount the bar in several locations left to right to adjust the placement of load on the rear tires upon acceleration. Moving the link to the left adds load to the left rear tire when we accelerate and loosen the car on entry.
Once you've made the turn entry better, check to see if your brake adjuster is centered. If it's too far to one side, changes to the brake master-cylinder sizes and/or pad compounds might be necessary in order to solve the bias problem and still maintain a centered bias adjuster. Off-centered adjusters can be inconsistent.
8. Bite Off the Corners When on dirt, we could always use more bite off the corners. The exit portion of the track provides little traction, and most corners are usually more flat. We almost always need to develop more rear traction upon acceleration. To give the car more rear traction, we need to understand a little about the dynamics at work on the car when we are accelerating.
We should work to develop ways to create more rear traction on acceleration only so we don't ruin mid-turn handling. There are several ways to do that without changing the handling at other points around the racetrack. One way is to reduce the "shock" of sudden application of throttle and torque to the rear wheels.
We can use lift arms and pull bars with various stiffness of shocks and springs. More and slower movement is needed for slick conditions and much less movement for the tackier conditions.
Another way to gain bite involves the use of a spring-loaded pushrod that allows a certain amount of forward right-rear-wheel movement to steer the rear end more to the left. As the car accelerates, the right-rear wheel moves forward, creating a slight amount of rear steer to the left. This points the forward thrust to the left of centerline and propels the car more efficiently, much like a sprint car.
9. The "Anti's" Anti-dive and anti-squat are mechanical influences that can help our transitional phases of entry and exit. We can regulate the amount of both depending on the need.
Chet Fillip shows me a remote...
Chet Fillip shows me a remote adjustable shock at PRI last December. This design makes the changing of the shock rates easy, even if you must, by rule, keep the adjuster out of reach of the driver. The car can come into the pit, and the crew can quickly make a shock change without having to jack up the car.
A small amount of anti-dive on our dirt cars can help prevent sudden nosedive on entry by utilizing mechanical resistance to the downward motion of the suspension. We do this by using the rotational forces created through braking.