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Old May 20th, 2019, 12:54 PM   #7
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ursle's Avatar
Join Date: Jun 2009
Location: NH
Posts: 1,871

Originally Posted by Mort View Post
Changing the height of the plate side cushion will make differences to how the plate steers. This is because of the way the compression starts to be applied to the truck yoke by the plate side cushion.

What's a side cushion?
What's a yoke?

Personally think this has a lot less to do with the pivot pin and more to do with the truck yoke ange vs the plate. By adding or removing height of the plate side cushion you will make the yoke sit either dead flat on the cushion and be on the same angle as the kingpin.

Decreased height will effectively reduce the kingpin angle. As well as make a small gap between the kingpin and the ivor pin, which changes the room/resistance there and doesnt allow the truck to turn as much.

What's an ivor pin?

When you increase the height over the point of where the yoke sits flat on a cushion it will effectively increase the angle the yoke sits on because it will begin to tilt the other way on the kingpin compared to a decreased height. Additionally there will be slightly more room on the other side of the truck yoke this way. This will allow the truck to twist more on the assembly as well. So the steering for given plate lean will increase.

This is considering you aren't cranking cushions WAY down which would practically negate any shimmying effect one would do. I know you don't, just saying if someone did, their results wouldn't be the same as yours.

Pivot angle is barely a difference when you consider the other conditions you are changing in a plate assembly when shimming cushion being up or down.

What's pivot angle?
Either the pivot pin is seated properly or it isn't, using shims to raise the hanger or removing urethane from a cushion to lower the hanger to adjust a non adjustable pivot pin is pretty basic, or to aid adjustment to an adjustable pivot pin.

The other thing I would guess is after you get past a certain amount of plate lean the plates will turn more like a unchanged cushion height(where unchanged means level and yoke is perpendicular to the kingpin). I don't know how much lean that would take before they started to turn the same though.
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