Steering geometry theory

Discussion in 'Recumbent bicycles' started by John Riley, May 7, 2003.

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  1. John Riley

    John Riley New Member

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    I spent some time on a Stratus last summer. When I was slowly grinding up steep hills, the bike felt quite wobbly to me. I haven't had the opportunity to spend equal time on a TE, but the TE has a rep for the best LWB direct steer handling. Some of the Strat people claim big improvements with different bars, but I felt there was more to it than that.

    I did some rough measuring at a dealer (me: old guy crouching uncomfortably on the floor with a yard stick and an angle finder). I looked at a GRR EX and a Stratus. These numbers are not precise, but here is the deal: both the Stratus and GRR seem to have 60 degree head angles. But the GRR has about a half an inch less fork rake, so the GRR ends up with about 3" of trail and the Strat has about HALF that. The differences in rake and trail are substantial. A bike shouldn't _need_ 3" of trail, so the extra rake may actually be the issue.

    If you could stick a fork from an EZ sport on a Strat (don't know if it would fit) that would tell the tale. The EZ has a 20" fork, as does the Strat, but the EZ fork has a lot less rake than the Strat fork.

    BTW, the EZ has a steeper head tube, but less rake than the GRR, so the trail seemed similar. For some reason the EZ feels like it has a bit more flop than the GRR when you ride it, even though it has a steeper angle (about 62) and less rake.

    Again, my numbers may be off, but I think the directions of the differences are correct. Or I could be all wrong ;-)

    johnriley1 (at) rogers.com
     
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  2. Tom Sherman

    Tom Sherman Guest

    John Riley wrote:
    >
    > I spent some time on a Stratus last summer. When I was slowly grinding up steep hills, the bike
    > felt quite wobbly to me. I haven't had the opportunity to spend equal time on a TE, but the TE has
    > a rep for the best LWB direct steer handling. Some of the Strat people claim big improvements with
    > different bars, but I felt there was more to it than that....

    I remember someone (Eric Vann?) reporting that putting Easy Racers handlebars and an Easy Racers
    fork on a RANS Stratus made the handling of the Stratus almost identical to the Easy Racer.

    Tom Sherman - Various HPV's Quad Cities USA (Illinois side)
     
  3. PaPa

    PaPa New Member

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    First, it’s important to remember that “steering geometry“, is only part of the equation. CG, wheelbase, tire choice (and pressure) and host of other factors need to be considered too. At the risk of being toasted, I find it a little disturbing that a handful of homebuilders seem to be advocating zero, or minimal trail (less than an inch), on LWB machines. Yes, the owner/builder/pilot may rightly prefer those settings, but certainly not all.

    Altering trail from, say 2” to near zero on a LWB machine increases input sensitivity. Some like this “sports car” feel. Many do not. A reasonable amount, say an inch or two of positive trail not only acts as a centering force, but also helps to absorb sudden changes in the steer wheel’s direction (such as off-center pebble strikes). Substituting trail for tiller (eliminating one for the other) doesn’t work for me.

    Plugging in a crude GRR side-view, I estimated 1.5”- 2” inches of trail. Knowing that, it’s becomes very difficult to ignore the thousands of happy TE/GRR owners. And Bob Bryant of Recumbent Cyclist News seems to agree, “You don’t know how many times I’ve heard people say that they didn’t believe me—until they finally experienced it for themselves. The handling of this bike is perfect.”
     
  4. John Riley

    John Riley Guest

  5. Tom Blum

    Tom Blum Guest

    Mark Stonich presents his theories on Recumbent steering geometry here. He feel that trail should be
    minimal to keep overall handling balanced. He has stated that large trail figures (2 inches +) only
    balance other shortcomings and cause problems, typically with fork flop or other slow speed
    characteristics.

    Read his method here: http://www.bikesmithdesign.com/Design/10Steps.html

    This method is specifically for Long Wheel Base bents. I don't know if it applies to SWB.I kind of
    think it does.

    I altered the steering set up on my Tour Easy Clone toward his recommendations and the results were
    very good. I still need to increase the fork rake to reduce trail a bit, but the reduced tiller
    improved handling a lot. Start up in noticeably improved.

    --
    Miles of Smiles,

    Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone

    www.gate.net/~teblum
     
  6. Hi, John, the last time I built an Easy Racer style machine I used a head angle of 58.7 degrees,
    rake of 3 1/4" and the trail was 2 7/16".

    It handles very well but I am currently building a frame that will only have about 1/2" of trail.

    I got this idea from Mark Stonich, who is a clever and successful builder, so I wanted to try out
    his steering geometry theories.

    Lewis.

    ...............

    John Riley <[email protected]> wrote in message
    news:<[email protected]>...
    > I spent some time on a Stratus last summer. When I was slowly grinding up steep hills, the bike
    > felt quite wobbly to me. I haven't had the opportunity to spend equal time on a TE, but the TE has
    > a rep for the best LWB direct steer handling. Some of the Strat people claim big improvements with
    > different bars, but I felt there was more to it than that.
    >
    > I did some rough measuring at a dealer (me: old guy crouching uncomfortably on the floor with a
    > yard stick and an angle finder). I looked at a GRR EX and a Stratus. These numbers are not
    > precise, but here is the deal: both the Stratus and GRR seem to have 60 degree head angles. But
    > the GRR has about a half an inch less fork rake, so the GRR ends up with about 3" of trail and the
    > Strat has about HALF that. The differences in rake and trail are substantial. A bike shouldn't
    > _need_ 3" of trail, so the extra rake may actually be the issue.
    >
    > If you could stick a fork from an EZ sport on a Strat (don't know if it would fit) that would tell
    > the tale. The EZ has a 20" fork, as does the Strat, but the EZ fork has a lot less rake than the
    > Strat fork.
    >
    > BTW, the EZ has a steeper head tube, but less rake than the GRR, so the trail seemed similar. For
    > some reason the EZ feels like it has a bit more flop than the GRR when you ride it, even though it
    > has a steeper angle (about 62) and less rake.
    >
    > Again, my numbers may be off, but I think the directions of the differences are correct. Or I
    > could be all wrong ;-)
    >
    > johnriley1 (at) rogers.com
     
  7. Lewis Campbell wrote:

    > It handles very well but I am currently building a frame that will only have about 1/2" of trail.

    The Kingcycle Mango had 15mm of trail, and look what happened to *that*... They have since modified
    it to give more - I don't know preciselt how much - and Young Master Robert reports that it felt
    much better in Manchester back in March.

    Dave Larrington - http://legslarry.crosswinds.net/
    ===========================================================
    Editor - British Human Power Club Newsletter
    http://www.bhpc.org.uk/
    ===========================================================
     
  8. Tom Sherman

    Tom Sherman Guest

    Dave Larrington wrote:
    >
    > Lewis Campbell wrote:
    >
    > > It handles very well but I am currently building a frame that will only have about 1/2" of
    > > trail.
    >
    > The Kingcycle Mango had 15mm of trail, and look what happened to *that*...

    But Rob English has the honor of having taken the record for fastest human powered crash at
    an estimated 70-mph (~110 kph), or about 10% faster than Fred Markham's [1] (Gold Rush)
    fastest crash. :)

    [1] He reported that the fairing shell became too hot to touch where it slid along the pavement,
    when he crashed at 60+ mph.

    Tom Sherman - Various HPV's Quad Cities USA (Illinois side)
     
  9. Tom Sherman wrote:

    > But Rob English has the honor of having taken the record for fastest human powered crash at an
    > estimated 70-mph (~110 kph), or about 10% faster than Fred Markham's [1] (Gold Rush) fastest
    > crash. :)

    Yes, I was there. It's probably the fastest *unpaced* human-powered crash, but... I don't have the
    reference here - does anyone have Issue 71 of the BHPC Newsletter to hand? - but a French rider
    crashed at a higher speed while going for a motor-paced record in, I think, the 1950's. No
    fairing. Ouch.

    Dave Larrington - http://legslarry.crosswinds.net/
    ===========================================================
    Editor - British Human Power Club Newsletter
    http://www.bhpc.org.uk/
    ===========================================================
     
  10. In an earlier lifetime, I owned a business building roadracing motorcycles. We specialized in
    chassis measurement and alteration, there were many aspects to the system, but trail was crucial to
    front grip. The GMDComputrack.com site will have some info, but for a true explaination, call one of
    the shops for more details.Wwe could measure a chassis and find the actual geometry in about an
    hour,this included rake, trail, swingarm downslope, clamp offset and others.
     
  11. If my memory is correct, John Howard (John Howard, Olympian and world speed record holder (155MPH!)
    ) crashed at a pretty high rate of speed when he was preparing for his record attempt.

    Lewis.

    ..................

    "Dave Larrington" <[email protected]> wrote in message
    news:<[email protected]>...
    > Tom Sherman wrote:
    >
    > > But Rob English has the honor of having taken the record for fastest human powered crash at an
    > > estimated 70-mph (~110 kph), or about 10% faster than Fred Markham's [1] (Gold Rush) fastest
    > > crash. :)
    >
    > Yes, I was there. It's probably the fastest *unpaced* human-powered crash, but... I don't have the
    > reference here - does anyone have Issue 71 of the BHPC Newsletter to hand? - but a French rider
    > crashed at a higher speed while going for a motor-paced record in, I think, the 1950's. No
    > fairing. Ouch.
    >
    > Dave Larrington - http://legslarry.crosswinds.net/
    > ===========================================================
    > Editor - British Human Power Club Newsletter
    > http://www.bhpc.org.uk/
    > ===========================================================
     
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