This modified has a "four...
This modified has a "four link" left rear suspension linkage and a Z-link swing arm on the right rear. Note the high angles (the rear axle is resting on a jackstand) of the links. This causes the axle on this side to roll under the forward mounts and load the left-rear tire under acceleration.
If you were to run different length steering arms to create Ackermann, turning one way might produce positive Ackermann and turning the other way would produce Reverse-Ackermann. This is unacceptable for any race car. So, other means (such as is done with stock passenger cars) must be employed to create Ackermann.
4. Alignment Alignment issues present just as serious a drawback for a dirt car as an asphalt car. There really is no reason to misalign the rear end. In tests we've participated in, we have run the same lap times with the car "sideways," due to excess rear steer, and when running it straight ahead with no rear steer.
We believe the rear end doesn't need to be any different in alignment than at 90 degrees to the centerline of the chassis and/or to the right-side tire contact patches, and those patches need to be inline, even on dirt.
It is difficult to maintain a correct driveshaft alignment on a dirt car. We should nonetheless try to start out with something that's close to ideal. The commonly accepted rule is, the angles between the driveshaft and both the pinion shaft and transmission-output shaft need to be equal and in opposite directions. This creates the lowest loss of power and the fewest vibration problems, which translates to longer U-joint/seal life.
The driveshaft doesn't care which view these angles are resulting from, only that they are equal and opposite. If we have a top view differential in alignment between the engine (crankshaft and transmission output shaft) and the pinion shaft and they are parallel, the angle created by that misalignment might be sufficient to provide needed angular differentials to load and lubricate the U-joint bearings.
A 1 1/2-inch misalignment with a 44-inch driveshaft results in nearly a 2-degree angle at both the tranny and pinion shafts. The engine should always be aligned perpendicular to the rear end and/or parallel to the centerline of the car.
5. Setup Balance Does a dirt car really need to be balanced? Of course it does. The balance, though, must be adjusted for the track conditions. If the track is tacky, the balance should be more like what we would do for asphalt, which is to match the desires of the front and rear suspensions.
The term "balance" means that both ends of the car have the same tendency to roll. The truth about setup dynamics is that at mid-turn, each end will want to roll to its own degree of angle. The relationship between those desired angles determines the balance of the car. On dirt, we can manipulate that balance relationship to adjust the car to different conditions.
Greatly unbalanced setups exhibit certain characteristics, such as an unusually high degree of wear and temperature on one tire versus the other tires, and an unwillingness to turn the corner. The unbalanced car will have less bite off the corners, and the handling will not be consistent.
The setup for slick tracks is with a controlled difference in balance in the front-to-rear relationship with the rear desiring to roll more so than the front. This provides more rear traction to give us more bite off the corners. If our MC design is correct, the car should still turn through the middle but have better traction off the slick corners.
This car is equipped with...
This car is equipped with sliding clamps mounted on square tubing. Adjustments to the link angles and J-bar heights can be made quickly and infinitely with this design.
6. Shocks Research on shock influences on dirt have shown 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 in the dirt-car market. The age old truth is that we need to perfect our setup first before working with the shocks.
Dirt cars show a lot of travel as they negotiate the four turns. This extreme degree of wheel travel means that shocks get to do more work than with other types of race cars. A shock does not have any influence if it is not moving.