outlines modifications to two bicycles to provide an
enhanced seating position for cycleway riding.
This simple project was inspired by riding a borrowed "Courier" folding bicycle
around the Redway System of Milton Keynes. Surprisingly, the Courier
provided an extremely comfortable and enjoyable ride. On closer
inspection it was apparent that the relative positions of the crank
and saddle were somewhat unusual.
The Courier was compared with a number of bicycles (pictured
below). To quantify the crank/saddle layout for each bicycle a line
was drawn from crank-centre to saddle-fixing-point and the
angle between this line and the vertical was measured (as illustrated
in the adjacent sketch of a Raleigh Monterey frame).
The results are listed below. Angles of
16° to 18° are fairly typical for modern bicycles. The large
angle measured on the Courier indicates that, compared with
contemporary bicycles, its saddle is significantly further aft
of the crank.
27° - Courier
16° - Ammaco Nova
18° - Apollo County
18° - Mountaineer
16° - Trek 7.3FX
18° - Raleigh Monterey
Indeed, the relative crank/saddle position of the Courier makes its layout
more akin to that of a vintage bicycle. The overlay illustration below
shows how the 'Ordinary' Bicycle (1880) and 'Rover Safety
Bicycle' (1886) have near-identical saddle positions - as measured
from the crank location. These relative crank/saddle positions are
very close to that of the Courier bicycle.
The Courier's performance suggests that, with regard to
cycleway riding, some vintage design features are still advantageous.
it's easy to assume that modern bicycle design is a
well-informed, highly technical process, the reality is possibly closer
to 'rule of thumb' and fashion.
In the magazine 'New Scientist', 28th May 2011, a feature entitled
'Easy Rider' explained that a formalization of the mathematics of bicycle
design has occurred only fairly recently. In the article, Andy
Ruina of Cornell University stated, modestly, that "the equations
started being written in 1898 - we just finally wrote them down clearly
In the same article, Rob van Regenmortel, then R & D manager of Batavus
BV said he anticipated that the newly formalized mathematics would probably
lead to future changes in wheelbase, seat tube angle and head tube
The above research
is very interesting but is something of a digression from the project
in hand. Although bicycle handling and performance is influenced
by a number of factors such as wheelbase, steering axis angle, fork
offset, and trail it was decided to keep the project simple. The Courier
has demonstrated a very comfortable, upright riding position. It was
decided to take two existing bicycles and use different approaches
to replicate the Courier's relative handlebar, saddle and crank positions.
The first subject for
experimentation was the Ammaco Zone (pictured right), purchased from
Hawk Cycles. The saddle / crank angle was already 23.5 degrees and so
it could be modified relatively easily to achieve the desired geometry.
The major change for the Zone would be the handlebars. Due to the variety
of proprietary handlebars available it was considered probable that
a suitable unit could be purchased, however, the geometry must be known
to be correct. The solution was to manufacture prototype handlebars in copper using a copper pipe bender.
The photo above shows the prototype handlebars fabricated from copper
tube. It was not possible to bend the handles into their ideal position
since the radius of the required bend near the handles was smaller than
the pipe bender could produce, however, it was sufficient to indicate
the required geometry.
It was found that cut-down BMX handlebars (that is small BMX handlebars
with approximately 1" cut off each end) were a very close match
to the geometry of the prototype copper handlebars. The BMX handlebars have the advantage of handles bent to the correct position. With
suitable handlebars purchased the project became one of simple assembly.
The new components included a short-reach stem, new road tyres and a
By rotating the saddle clamp such
that the nuts were aft of the seat post and by sliding the saddle all
the way back along its rails, the
handlebar/crank/saddle could be made to match the courier's geometry
exactly (shown in yellow below).
The result - the finished bicycle is wonderful to ride with its upright seating
The second project used a Raleigh Monterey. Modifying the
frame by cutting and welding new tube was considered initially. The
proposed modified frame design is shown
in green in the figure
To test the design concept, the Zone's copper handlebars and
newly manufactured copper layback seat
post were fitted to the Monterey. The test showed that the
concept was a good one although the twisting moments that cycling would
the layback seatpost meant
that the fitting would have to be very robust. At this
point it no longer appeared necessary to modify the Monterey
frame. A purpose-built steel layback seat post and modified steel BMX
handlebars were used to create the required geometry.
The layback seatpost was cut from a scrap steel chair frame. Originally,
it was envisaged that the correct bend in this 1" steel tube would be
achieved by cutting a series of slots (see photo below), bending the
tube to the desired angle and then welding it using a MIG welding machine
However, the chair frame was cut in such a way that it made
use of a bend
already incorporated into the frame. As chance would have it the angle
was perfect for the Monterey's layback seat post.
The only downside to
using this pre-formed tube is that the metal is 'drawn' around the
bend (i.e. the tube is thinner in the vicinity of the bend).
This means that the seat post clamp is less effective and hence a
self-tapping screw was required to fix the post in the tube and prevent
the layback seat post from rotating. A second screw was used in the
saddle clamp to prevent the saddle rotating about the seat post. The
clamp itself had been cut to fit over the 25.4mm post (the
clamp was originally 22.2mm). The finished bicycle used a new
modified steel BMX handlebars and a new steel layback seat post
From the photo on the left it can be seen that the new Monterey layout matches
the Courier's geometry (in yellow) reasonably well. With the frame itself
unmodified, the handlebars are slightly too far forward, however, this
is more than made up for by the ease with which the task was achieved
and the fact that the original configuration can be regained with the
minimum of work.
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