Recumbent Racer Virtual Hub Center Steering Closeup with Video - Not your father's front suspension

Bob Horn taking a right hand turn at speed in his recumbent racer

Bob Horn taking a right hand turn at speed in his recumbent racer

After showing you Bob Horn's excellent recumbent racer project, the Kawasaki EXperimental500, some of you were curious about how the steering worked. It's far better to show it in action than try to explain it, so Bob shot this short video from several angles and you can see for yourself.

Closeup detail of the steering and front suspension in Bob Horn's recumbent racer

Closeup detail of the steering and front suspension in Bob Horn's recumbent racer

I will not attempt to do more than show it to you, Bob will have to be the one to answer any questions. So watch the video and ask away.

Closeup detail of the steering and front suspension in Bob Horn's recumbent racer

Closeup detail of the steering and front suspension in Bob Horn's recumbent racer

Link: Rohorn.com

Comments

  1. Old Guy says

    Is there any kind of trail or kingpin inclination on the fork? Very clever design on the lower struts using the heim joints instead of opting for a large diameter bearing with a slotted centre section. Does it cause any lateral side to side movement of the forks as the distance to wheel centre changes?

  2. says

    Trail is just over 4″ with a 19 degree steering axis angle. There is the usual side to side movement at the front end, even though the trail doesn’t move in the same arc that a steering head (Or “normal” hub center steering) would have.

    • Anthony says

      This seems to me like a very clever and well-considered (and constructed) advancement of the OEC duplex system. This design is far better in allowing variation of trail and a decent turning circle, both deficient in the OEC design. More strength to you, Sir!

    • Ken says

      The fork looks very vertical. Is the trail and steering angle achieved by virtue of the instantaneous center of the two bottom struts way ahead of the upper heim joint?

      Very ingenious stuff!

  3. Erik says

    I had a very similar idea but it never left my head. Props to Bob for taking it out of his head and into the real world.

    A further evolution of the design would be to adjust the angle between the upper and lower arms from the side view to build in anti-dive.

  4. Mark L. says

    How does it “feel” for steering? My guess is that you get some interesting wear on the front tire, but I would think the “feel” would be normalish….

    Kudos to you for an excellent solution to some expensive alternatives on the front end!

    Good luck!

    Mark L.

  5. Bob Horn says

    Erik, Mark,

    Thanks!

    The first bike I used a virtual pivot (The Harley project from over 20 years ago) had anti-dive geometry – it worked perfectly for the way I rode on the street, especially up in the mountains (Those were fun days!!!!). But for a lower CG bike with a longer wheelbase, I thought a lower “Pitch center” (Think “Roll center” dynamics used on car suspensions turned sideways) would let the brakes settle the front end to match the settling that naturally occurs under hard cornering – that works perfectly for the way I ride at the track.

    The front tire does wear a little differently with the steeper steering geometry. I initially had a lot of wear from too much trail braking after rolling into the corner and up to the apex. I reduced my lap times a lot by just cornering harder instead for now. Will revisit my cornering/braking technique when I get my speeds up and get more competitive.

    Feel? LOTS! One benefit that they never talk about with this configuration is that the handlebars are just that – bars for your hands – they aren’t used for immobilising or mobilising your body. And when you’re stretched out the entire length of the bike AND most of your body is in contact with it, you feel changes in traction at one end or the other vastly better.

    • Richard Thompson says

      Bob, due to the unusual geometry, do you get any excessive feedback or instability while cornering over bumps and irregular surfaces? Something like bumpsteer, but in this case due to dynamic side forces on the front wheel?
      I thought it might be so as the steering axis seems to slant sideways.
      Very interesting design.
      Thanks for your attention.

      • says

        I’ve never felt anything remotely disturbing about the front end’s feedback or tracking.

        The steering axis does move to the side with increased steering sweep – it eliminates much of the “Pendulum effect” that normally occurs with trail – and does a lot to lower wobble potential. That, in turn (hah), allows faster than normal steering geometry!

        Thanks for asking!

  6. Josh says

    Thanks for the vid! Now I can finally wrap my brain around how it all works together.. ;D

  7. Dr Robert Harms says

    Its an impressive piece of work I especially like the fact that he concentrated on the engineering and functionality rather than the aesthetics

  8. Paulinator says

    I used this type of mechanism on a couple of hand-cycles. The layout has inherent benefits regarding frame stresses – especially with a very light weight HPV that has to suffer the torture of hand-cranks in place of the handle bars. I dialed-in a ton of caster to put the front wheel on the “correct” side during a hard turn, greatly reducing any tendency to tip. I also reduced front-end drop to virtually nothing. The end result was an extremely stable three-wheeler with a 10 foot turning circle.

    I modified my second hand-cycle to “bicycle” configuration and had to dial back the caster, but the stability was still very good…until a bearing seized in one of the hand-grips. I had no sensation of the extra drag in the hand grip. I only felt the problem thru my ass as I slid down the road.

  9. says

    Bravo Bob
    A man after my own heart who breaks all the rules. And nicely done with it.
    My own attempt at a ghost point system, which I first saw on the BMW 7 series cars didn’t escape my drawing board. Do I see a rule breaking back end as well?
    Hats off to you.
    Norman Hossack

  10. dave woolard says

    Really nice to see an application of this! When braking in anything other than a straight line do you get a pull on the steering? and is it significant?

    DaveW

    • says

      No “Standing up in the corner” effect or any other weirdness noted. That said, only light trail braking has been done while cornering (The long wheelbase and low CG means the front tire doesn’t get as much weight transfer – so the front end tends to push a bit when only the front brake is used). The skinny front tire has something to do with the neutral steering while on the brake as well, I think.

      Thanks!