Steering Design

The lean-steering illustrated here was based partly on the Varna trikes that use a principle also found on the humble skateboard. Tilting a skateboard causes the front axle to pivot (the wheels remain parallel to each other). The degree of this effect depends on the angle of the pivot relative to the ground. If the angle is such that a line extended through the pivot would touch the ground at a point where the rear wheel contacts the ground, there would be zero steering effect. A steeper angle, bringing this point forward, gives a stronger steering effect. The composite picture shows the main tube and cross-beam seen from directly above. The cross-beam remains parallel to the ground but turns to the left or right while the main tube swings below it as the rear wheel leans over to the left or right.

Because the rider's body leans into the turn, the CENTER OF GRAVITY moves to counteract the cornering forces that cause the inner front wheel to lift off the ground. This is shown in the following two front-views:

For the purpose of experimenting, I have made the angle of the head tube adjustable. In the following pictures and the picture on the previous page the angle is such that the axis meets the ground at the same point as the rear wheel. However, when the angle is very small the minimum turning circle is very big. So, to gain more steering effect I have combined the skateboard principle with a set of conventional kingpins and link rods in such a way as to increase the degree of steering when you lean in to turn. Details are seen in the following views of the mechanism. The second shows the frame upside down:

With this design a very small turning circle is possible without having to lean very far over. The degree of this compounding depends on the distance between the axis of the pivot and the attachment point of the link rods. This point can be adjusted using the holes drilled in the mounting plate seen in the second illustration above.

The kingpins are linked horizontally by the cross-beam seen in the pictures above. The following picture shows the kingpin sub-assembly without the cross-beam attached to the hoop which serves as hand-hold for the rider and which passes over the rider's legs. This is an essential structural component, made of 3/4" square steel tubing. It takes a lot of the braking torque, and when leaning at low speeds the rider exerts a great deal of force onto this hoop to keep from falling over sideways. The brake lever is also visible here (front view):

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(1 February 1998).