[python] Re: Evij-trike with suspension forks - conclusion: bad idea
- From: Patrick van Gompel <patrick_van_gompel@xxxxxxxxxxx>
- To: <python@xxxxxxxxxxxxx>
- Date: Fri, 5 Aug 2011 11:46:18 +0200
A different point of view...
Although it might seem logic that the rear wheel moves up and backwards when
hitting a bump, the Cane Creek manufacturer of seat post suspension puts it
another way.
Quote:
"Thudbuster
Technology
The Key: Working in the direct path of the natural travel of the rear wheel.
The inherent dynamics of a bicycle create a rocking motion, meaning each end
arcs around the other end. Specifically, the rear wheel moves on an arc that
has the front axle as its center, and the front wheel moves on an arc that has
the rear axle as its center.
As a bump lifts the rear wheel, the rear wheel pushes the saddle up and forward
into the rider. The Thudbuster compresses along the exact opposite path
(downward, rearward) to absorb force. The Thudbuster moves down and back at the
same rate as the bump comes up and forward, so the net movement of the saddle
is zero.
Telescoping suspension seatposts have a compression stroke in the vertical
plane. As the bump force travels up and forward through the rear wheel, the
seatpost suspension is more than 50 degrees out of line with the bump forces.
Since 90 degrees out of line is complete mechanical lockout, telescoping
seatposts are halfway to lockout by design. This is much less efficient than
the fully active Thudbuster design."
My personal point of view for a recumbent is that a rear or forward directed
seat suspension will always work against your pedal input which is in the same
direction (as Uipko already said). So I guess you would want it to be vertical
for seat suspension. But, seat suspension is different from wheel suspension.
Using suspension forks like in the mentioned picture
(http://en.openbike.org/wiki/File:Evij-trike.jpg) doesn't seem like a problem
to me. There won't be much negative pedal input, since the suspension is
attached to the wheels, not the seat. And the direction of suspension travel is
in the right direction according to Cane Creek's description. The only problem
I could think of, is that when the fork suspension is too soft, you might get
difficulty while cornering. Leaning of your body might be more important as the
natural direction of leaning of the trike is the wrong way.
I am not at all an expert, but I thought a second opinion would add a few cents,
Patrick
> Date: Fri, 5 Aug 2011 09:07:50 +0200
> From: bnmm@xxxxxxx
> To: python@xxxxxxxxxxxxx
> Subject: [python] Re: Evij-trike with suspension forks - conclusion: bad idea
>
> Uipko,
>
>
> > would it be possible to use suspension forks with a design like
> > this? (using python steering)
> > www.openbike.org/wiki/File:Evij-trike.jpg
> >
> > It seems that the forks are inclined ca 45°, would there be too much
> > shearing strain? Else, if it works ok, is it a good idea in the
> > first place or would it be better to suspend back rest or seat
> > instead?
>
> >> If I look at the picture my guess would be that the suspension
> >> will manly work to absorb you put on the pedals and not flatten out
> >> the bumbs in the road. This because they are pointing back instead
> >> of forward. If you imagine a bumb hitting the back wheels where do
> >> they want to go? The wheels want to go up and to the back and not
> >> to the front.
>
> Yes, I agree with both objections, seems like a bad idea after all.
>
>
> Cheers,
> Marek
>
>
> --
> Marek Möhling
> Naunynstr. 82
> 10997 Berlin
> Germany
> Tel: +49 30 347 676 95
> Fax: +49 30 484 988 218
>
> On 05.08.2011 08:43, Uipko Berghuis wrote:
> > Hi Marek,
> >
> > On Fri, Aug 5, 2011 at 12:56 AM, bnmm@xxxxxxx <bnmm@xxxxxxx> wrote:
> >> would it be possible to use suspension forks with a design like
> >> this? (using python steering)
> >> www.openbike.org/wiki/File:Evij-trike.jpg
> >
> > If I look at the picture my guess would be that the suspension will
> > manly work to absorb you put on the pedals and not flatten out the
> > bumbs in the road. This because they are pointing back instead of
> > forward. If you imagine a bumb hitting the back wheels where do they
> > want to go? The wheels want to go up and to the back and not to the
> > front.
> >
> >
> > Uipko ============================================================
> >
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