- From: Frank Bokhorst BOKKIE@psipsy.uct.ac.za
Date: Tue, 13 Jul 1999 10:08:22 SAST-2
Just recently I built a parallel link front suspension
for my trusty old upright commuting bike. It also
includes a disk brake. At first it seemed scary to
attempt such a seemingly high-tech project, especially
for the FRONT of an UPRIGHT bike! However, it was
successful, and now in daily use, and I am very happy
with it. Can do low-tech!
A detailed description of the suspension/disk brake is at:
- http://www2.bitstream.net/~mstonich/MNbikes/pix/brick11s.jpg & http://www2.bitstream.net/~mstonich/MNbikes/pix/brick05.jpg
- From: Rick
Subject: [trikes] Rear suspension/pogo chain line
I have read this thread with much amusement. Currently,
I'm making last minute changes on a rear suspension
system I am building for a trike. I've experimented with
a couple of prototypes and have recorded some raw data
concerning the tension of the chain in relationship to
the vertical wheel force. However, this data is not at my
disposal at the moment, but I do have some conclusions
that may be of interest.
As many people have noted, the active chain line should
intersect the pivot axis of the swing arm. Ideally this
is true, as any chain line deviation from the pivot axis
produces a non-linear vertical force to the rear wheel.
The good news is that the chain can wander off this
intersection by a few degrees with minimal consequence.
Having a large or small tooth count on the rear cluster
does not affect the suspension as long as the chain
intersects the pivot axis.
Recumbent rear suspension is not as critical as a
mountain bike suspension. Remember that on a mountain
bike, the bottom bracket and cranks are placed generally
below and in close proximity to the swing arm pivot axis.
Consequently, when pedaling is applied, the bike has a
tendency to pogo. A recumbent has the bottom bracket out
forward and away from the pivot axis. Therefore, the pogo
effect is minimized. However, there is always exceptions.
let's say we want 15 cm(6 inches)of travel on our trike .
Well, the deflection rate is simply Kg per cm. On an
undampened, linear steel spring suspension system the
back-end is going to pogo regardless of the conditions.
However, if we restrict the amount of suspension travel
to 7.5 cm (3 inches), have an axle deflection rate of 80
Kg per 2.5 cm of travel (175Lb. per 1") and use some
type of viscous dampening, the rear end becomes
increasingly stable, hence no pogo.
Another question I noticed was why would the pulley or
mid drive be mounted on the swing arm pivot axis. Using
the swing arm pivot axle is a practical approach. If the
pulley (or mid drive)were placed in an optimum location,
the cost and weight of the vehicle would increase. The
increase in weight and cost may not justify the minimal
improvement in suspension performance. Of course the
conclusion is left to the designer.
From: Carey Chen
'How can I attach a
aluminum hub, probably with compound curves to a cro-mo hub?'
Bolt it to the frame, on the first big WHIRL ride in 1998, there
was a home build that used such a setup. It used a rear hub which
also had the intermediate drive as part of it.
'Better yet, how can I
reproduce the necessary structure to support the bearings for the
This bike had the hub bolted to the frame by drilling out the
spoke holes, for I guess 5mm bolts.
And maybe, how to make the
rear arm rigid, since its hinge end is "open" like
forks. This is probably not an issue, just make it long enough
and run some cross pieces.
On Alan's Outlander 22 the rear swing arm pivot is the rear axle
assembly from a Suntour Grease Guard hub. This has a 10mm axle
with sealed cartridge bearings. The cartridge bearings are held
in the frame by a tube that looks like a BB shell. The swing arm
is adjustable in the horizontal axis and the longitudinal axis.
The horizontal axis is done with what looks like forward facing
track drop outs. The other is done with shims and set screws. The
swingarm it self is made of 1" square steel tube with 2
cross members, plus a plate on which the elastomer pushes on. It
is very rigid.
At first thought the normal bike bottom bracket
would be the obvious choice for a suspension
pivot. The difficulty I have with it is I haven't
found an easy way to make it so the bearings can
be serviced and the rear forks removed.
a simple to build suspension joint that can
easily be removed for bearing adjustment and is
made with normal bike steering head parts. To get
a symetrical joint 2 threaded fork stems will
need to be butt welded together if you can't
thread the tubing.
2 bike steering head stems are cut down so
both sides can fit inside the pivot. A washer is
welded to the end of the head stems for the bolt
to pass through.
Thursday, 29 January 2009