Spindles come in all shapes...
Spindles come in all shapes and sizes. This 31/44-scale race car has spindles fabricated out of steel tubing and uses Heim joints for the ball joints. The ball joint heights are adjusted by spacing the Heim joints off the tubing.
We speak as often as we can about the moment center (MC) and its importance to the dynamics of the front of our race cars. It has been proven by countless racers on dirt and asphalt that this one invisible point can cause more headaches than most settings on the car. It is literally the center of the race car chassis universe.
The problem arises in knowing how to properly make changes that will move the MC to the desired location. Changes can be made in several different areas, or a combination of areas, to manipulate the location of the MC. Let's take a look at the various areas in which we can usually work and see exactly what we would need to do to affect our MC location. If for some reason you cannot work with any of these areas, work where you can, but try to move your MC to a position where it will do you the most good.
There are three main areas where we can work to change the arm angles. These are the chassis, the control arm lengths, and the spindle. The spindle may be easier to change than the chassis in most cases, especially when working on a stock clip car with rules that don't allow changes to the chassis mounts.
The relationship of the upper...
The relationship of the upper and lower control arm angles produces an invisible point called a moment center. The position of the spindles and the chassis attachment points determine the angles. The location of these points is extremely important to the car's turning ability.
Many times we're faced with incorrect arm angles because of a spindle that is either too short (usually) or too tall. If we can find a spindle with different dimensions, we may be closer to having the correct arm angles than if we move the chassis points. Besides, there are mechanical restrictions to moving certain chassis points, such as the lower chassis mounts.
In many cases, a car will have too little upper control arm angle and too much lower control arm angle. This is a result of having a spindle that is too short. Remember the spindle pin or hub is always in the same place vertically if we use the same tire circumference. We can change the height of the spindle so we can move the upper and/or lower ball joints to affect the arm angles.
If we change from a 731/44-inch-tall spindle with an offset of 311/42 inches from the bottom of the spindle to the center of the pin to an 811/42-inch-tall spindle with a 311/42-inch offset from the bottom to the pin center, then we have raised the upper ball joint by 31/44 inch and not changed the lower control arm angle.
We can install a 911/44-inch-tall spindle with a 411/42-inch offset from the bottom to the pin and gain 11/42 inch of height on the upper ball joint while lowering the bottom ball joint by 1 inch. This increases the upper control arm angle and also reduces the lower control arm angle.
For stock applications, the...
For stock applications, the upper control arm angle may well run uphill from the ball joint to the chassis. This is terrible for moment center design as well as for camber change. We need to lower the chassis mount and find a longer "stock" spindle to take this spindle's place.
The type of ball joint we use can affect the control arm angles. A standard K-6141 press-in lower ball joint is 31/48 inch shorter than a K-6117 press-in lower ball joint. Using the longer part reduces the lower control arm angle. There are also aftermarket ball joint manufacturers who offer different-length ball joints.
For years, Coleman Racing Products has offered a mono-ball replacement for the upper and lower ball joints. These units are adjustable in height by moving spacers above and below the mono-ball. Howe Racing Enterprises offers its precision ball joint replacements that are interchangeable with the upper and lower ball joints. You can order longer replacement studs for Howe's ball joint in plus lengths from +0.1 inch to +0.5 inch in 11/410-inch increments.
Spindle Quality Control
Another factor concerning spindles that goes unnoticed is in the way the builder of the spindle taps the tapered holes that the ball joint stud goes through. To date, we have not heard of anyone checking the depth of taper on each spindle. If this dimension is not kept consistent, each spindle may be of a different length between the centers of rotation of the upper and lower ball joints. You conceivably could install two 911/44-inch-tall spindles on your car and one might be longer, ball joint to ball joint, than the other