[PVD] pivot bearings

[Peter Verdone]

The ground effect racing truck uses two flanged cylindrical plane bearings to facilitate its pivot action. These are the best choice of bearings for a skateboard truck since the motion is only along a single axis and merely needs to be supported along it. They provide considerable amount of surface area for support. They are cheap, provide very little frictional resistance both about and along the steering axis and they are very light.

Other high end manufacturers of trucks have decided to use paired spherical plane bearings other wise known as Heim bearings (they have decided to call them knuckle bearings!?!?). While a pair of these bearings can be used to establish a single pivot axis, they are not ideally suited for this task. Spherical bearings are meant to be used when motion and forces are directed about many axes with a small amount of rotation. They are not only heavy and expensive, but they have relatively poor bearing qualities when high loads and fast speeds are concerned. They are also extremely prone to contamination when not sealed. When configured in a perpendicular fashion, the angular limits are restricted by bearing lying down, between 7.5 and 10.5 degrees (for a 3/8 bearing) depending on how the bearing is seated.

Just about everyone else establishes an approximate axis by holding the hanger between grommets. Not only is this a very crude way of establishing this axis but it is prone to shifting and storing twisting forces not associated with control. Also, other than Randal, some gullwings and old trackers, the pivot cup is not lined up with the axis at all. This would be to build vertical strength into their design at the expense of steering quality.