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So far I've found two types of steering aside from the classic direct steering ( Handlebar->Stem->Fork->Wheel rotating in head tube bearings (headset)) that eliminate the head tube, used in a few cargo bikes:

  1. Hub-center steering moves the bearings inside the hub, compact and thus elegant, but requires complicated parts (Elian, Dan Titchmarsh, Bastiaen, machined parts)
  2. A four bar linkage that is big(ger) but easy to build, with the tradeoff that there is no constant "virtual" axis of rotation, i.e. the wheel moves relative to the frame, depending on the linkage geometry (Escargo, XYZ Cargo Bike(steering, video), Catan, Veloader, Cargonnect).
    Of course that depends on the linkage - a design with more links allows a fixed pivot.

A simple sketch, top view:
enter image description here

It seems I got lucky there, the cyan trace shows that the motion is less than the tire width.

Youtuber erik warnerin gambalgembelart has collected a few more:

Questions:

  • Is there a name for this type of steering system?
  • Are there more implementations / specimen of this?
  • What are the design considerations / optimal geometry for this (zero displacement or is some displacement actually advantageous?)?
  • Are there other designs (to eliminate the head tube bearing)?
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    Actually, I've come across another, from the maker of the Escargo: the Y-Cycle with 56 degrees of rake (horizontal fork).
    – handle
    Commented Apr 26, 2022 at 11:07
  • Reer wheel steering linkage (video) on a recumbent, a comment calls it "trapezoidal steering linkage".
    – handle
    Commented Apr 27, 2022 at 7:25
  • From your question I can not work out whether you indicate the steering of a Flevo bike/trike/high racer, where the front wheel is fixed into the front part of the frame and the frame has a pivot point in the middle of the total length. Here is a link to a picture of one of those bikes: nl.wikipedia.org/wiki/Bestand:Flevobike-air.jpg
    – Willeke
    Commented Apr 27, 2022 at 9:21
  • @Willeke No, I don't mean center / articulated steering. Have a look at one of the examples listed in the 2nd bullet point, e.g. the Catan, especially the section "Leading linkage arm steering system". The "arms" are shown in red in my sketch.
    – handle
    Commented Apr 27, 2022 at 14:47
  • Might I suggest calling this "headless steering"?
    – handle
    Commented Apr 27, 2022 at 17:19

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