4. Alignment

It has been found that the misalignment of your tires/wheels present serious drawbacks to a finely tuned chassis and setup. Alignment issues are defined as: A. rearend alignment, B. contact patch alignment, C. driveshaft to pinion/transmission alignment, and D. front and rear toe.

The rearend needs to be aligned at 90 degrees to the centerline of the chassis and/or to a line through the center of the right side tire contact patches. The right side tire contact patches will also need to be inline with the right front tire pointed straight ahead.

The driveshaft alignment is critical from the standpoint of mechanical efficiency. Loss of efficiency can rob power from the drivetrain due to the generation of vibrations and harmonics that are also damaging to the bearings.

The overall general rule is that the angles between the driveshaft and both the pinion shaft and the transmission output shaft need to be equal and in opposite directions. The less angle the better.

The driveshaft doesn't know which view these angles are resulting from, just that they are equal and opposite. If we have a top view difference in alignment between the transmission output shaft and the pinion shaft and they are parallel, then the angle to the driveshaft created by that misalignment might be sufficient to provide the angular differential needed for loading the U-joint bearings and reducing negative harmonics.

A 11/2 inch top view misalignment with a 44-inch driveshaft results in nearly 2 degrees of angle at both the tranny and the pinion shafts. The engine should always be aligned perpendicular to the rearend. This would mean we could align the driveshaft from a side view inline with the tranny shaft and the pinion shaft with no angular deflection.

5. Setup Balance

Balance is spoken of in all types of motorsports these days, even F1. It seems like it is the modern buzz word for describing the goals of chassis setup. Here is an explanation of balance related to the dynamics of the race car.

The setup we choose needs to be arranged so that the dynamics are balanced between the front and the rear suspensions. Each suspension system desires to do its own thing when lateral forces are introduced from the car going through the turns. These desires are directly influenced by the spring stiffness, location and spring split, the sprung weight the system has to support, along with the moment center locations and other settings.

Each end of the car has its own moment arm length and resistance to roll as well as other factors. The bottom line is that at mid-turn, each end will want to roll to its own degree of angle. That is the best description of the result of the dynamic force that influences each system. If those desired angles are different, then we term the setup unbalanced.

Unbalanced setups exhibit easily observed characteristics, such as unusually high degree of wear and temperature on one tire versus the other tires. The car may or may not be neutral in handling, but the handling will not be consistent. You must try to determine if your setup is balanced and then if not, make the necessary changes to bring it into a balanced state.

6. Shocks

Once you have evaluated all of the above and feel fairly confident that the car is setup 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 unless you are running on a bump fixture, then you need to match the shock rebound to the spring rate of the fixture, which is much higher than the ride spring rate in most cases.

Shocks affect 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 are trying to control.

7. Brake Bias

Once the setup has been balanced and the shocks are decided on, we need to evaluate the turn entry characteristics and brake bias is a very important influence at this segment of the track. We do not want to try to solve turn entry problems with the brake bias, we only need to make sure the car stays neutral in handling when the brakes are applied.

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 is 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.