How to make an In Head Suspension for an HPV or recumbent bike
Headshock V2

By Warren Beauchamp

This version of the headshock is much simplified and lightened, and utilizes an Polyurethane elastomer for it's bounce. It is much more robust than the Headshock V1 (below), and is easier to build. As elastomers are self-damping, the rebound present in some spring based systems is eliminated. The elastomer used in this design is available in 40A or 60A durometer. 40A is about the consistency of a pencil eraser, and 60A is about the consistency of tire rubber. This system fits in a standard 1" steerer tube, making it easy to retrofit existing bikes. Also see FWD Suspension.

Click on the image for a larger view
Notes: 
  • The steerer tube is bored to a unform 7/8"ID, and 7/8" OD press fit sleeve bearings are pressed in. 
  • A 3/4" OD chrome moly tube is welded to the fork. This tube slides freely in the sleeve bearings
  • The Polyurethane rod is cut to the desired length (depending on amount of travel desired) and a 7/8" clearance hole is bored through the center. 
  • 1/16" flanges are braised to the tubes to support the elastomer.
  • A 7/8" OD tubing clamp is used on the top of the fork to limit the suspension top-out, and to attach the handlebar riser. (Yes it's shown sideways in the drawing). This means that the road shock will be transmitted to the handlebars, but this will not affect the ride quality or handling.
Parts and suppliers listed below:
Part Quan Description Distributor Part Num Cost
1 2 Bronze plain sleeve bearing McMaster-Carr 6391K207 $0.97 ea
2 1 40A or 60A durometer 1-3/4" dia by 6" long Polyurethane rod McMaster-Carr 8695K182 $21.94 ea
3 1 ft .075" x 1.5" - .049 wall chrome moly rectangular tubing Wicks Aircraft RC3/4x1-1/2x049 $7.13/ft
4 3 ft 1.180" x .5" - .035 wall streamline chrome moly tubing Wicks Aircraft SL11-50-3 $9.90/ft
5 1 foot 3/4" OD - .120 wall chrome moly tubing Wicks Aircraft R3/4x120-41 $3.20/ft

HeadShock V1 or How to make an In-head front suspension
By Warren Beauchamp
After a discussion on the low-racer mail list, I decided to diagram how to build a front suspension similar to the one currently used in the WISIL Missile, which was built by Rick Wianecki and Bill Murphy. This suspension design is very compact, being entirely inside the head tube. The travel of this type of suspension is limited to about 2 inches, but that is all that is needed for on-road, or racing applications. The knee joint in the drawing below allows an up and down motion while transferring steering force to from the steering tube, to the fork. The handlebars need to be clamped or welded to the outside of the steerer tube. The Pre-tensioner bolt should be tightened to provide the proper amount of travel. Bronze bushings are press fit into 1" steerer tube, these bushings have a 3/4" ID. A 3/4" OD, 0.092" wall thickness chrome moly tube is braised to the fork (green tube below).  A certain amount of stiction will occur with this design, which in operation works quite well to provide needed dampening. A custom knee joint based system similar to this has been used by Lightning and BikeE for their front shock. 

headshock1.jpg (41969 bytes)

 

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