A stonger and lighter fork

For a negative steering axis design, the fork needs to be stronger than when the fork points forward in the conventional manner. The old steering tube design was replaced with a sturdy custom-built fork that pivots on an industrial strength needle roller bearing close to the point of maximum stress, and a ball bearing located at the top of the tube to take axial (vertical) loads.

The fork was designed with dropouts and mounting lugs for the Rohloff 14-speed hub and Magura Louise disk brake caliper. It is shown below in a semi-finished state, with the chain idler pulley in place. Lugs for the steering linkages are also visible.

The old bottom-bracket, pirated from a conventional bike, was replaced with a custom-built sub-frame designed for the loads encountered with the recumbent pedalling position. Here the new subframe is shown attached to the older mid-section of the bike. The picture also clearly shows the cups into which the lower needle bearing and upper ball bearings on the fork tube will be fitted.

Emergency Roller

This is a useful precaution against the possible collapse of a backward-leaning front fork. If the fork were to bend backward, for example from a bad pothole, the front tyre would be pushed against the fairing and bring the bike to a sudden halt! To allow the wheel to continue turning in this event, a small but sturdy roller was fitted to the frame just where the tyre would hit it, as shown in the picture below.

Hope I never need it!

Rohloff hub gear

Below you can see the Magura disk brake and external shifter box with dual cable routing for the Rohloff hub. Note the quick-release dropout designed for the Rohloff OEM version that requires no torque arm. Transmission torque is taken by a small stub that slots into the left dropout. Note: the front of the bike is to the left in this picture.

In the next picture you can see the small "crash bar" made from 1/4 inch thick stainless steel welded to the fork to protect the gear change mechanism and brake hydraulics. If the bike falls on its side, this crash bar and a steel bar projecting from the rear tailbox fairing, together also ensure that and fragile parts of the very costly hydraulic brake lever do not contact the road surface.

The Rohloff dual-cable twist grip shifter is shown below. Note that it has been modified to suit the steering controls. Both sticks are fitted with knobs on their ends since mostly the rider's hands do not grip the sticks but rest on their ends. The Rohloff twist grip shifter has an extra large wooden knob, fitted into a short section of rubber radiator hose that caps the relatively tiny Rohloff shifter. Unfortunately, the nature of the parallel stick steering controls is such that twisting the shifter tends to upset the steering. The much larger diameter of the modified grip makes gear shifting lighter, even with only one hand on the controls. The Magura hydraulic brake lever is on the left side (as is the disk itself). Also visible are the short projections extending from the fairing at the level of the seat, which are part of the "crash bar" design.

Chain routing

Click on the picture below to download a short Quicktime video clip (approx. 700k bytes) showing how the chain twists with the steering.


Creted: March 2001