topics: |  bicycling | design

Mike Burrows is a legendary bicycle designer with a wide range of credits
from the recumbent Windcheetah and Ratcatcher to the LotusSport time trial
bicycle monocoque frames, and the sloping down-tube innovation on the
canonical diamond frame, to the 8-freight delivery bicycle.

The book is written in a lively style, but sometimes the arguments are not
fleshed out enough.  Uncovers the many intricacies of bicycle performance
and design, and demolishes many myths along the way.

BIO: His father ran an aeromodelling shop, and as a child he got involved in
building model airplanes from an early age.  Eventually he dropped out of
school and started riding and designing machines, and turned to bicycle
racing.  He designed the recumbent tricycle Windcheetah which became a
landmark in Human Powered Vehicle design.  Subsequently he became partner in
a firm making packaging machines, but eventually joined Lotus and created the
LotusSport Pursuit bicycle which was ridden to a gold medal by Chris Boardman
at the 1992 olympics.  Subsequently he also worked with Graeme Obree who
broke several one hour records.  Was hired by the leading
Taiwanese firm Giant cycles, for whom he built the MCR racing bicycle with a
monocoque frame.   He also pioneered monoblade design where the wheel is
cantilevered from an aerodynamic strut on only one side (e.g. the Ratcatcher
recumbents).

Who invented the bicycle?

 
  The Laufsmaschine (Running machine) designed by Karl Drais in 1817, is
  considered to be the first vehicle to demonstrate the idea of two-wheel
  balance

Baron Karl von Drais ... took the most remarkable first step when he
discovered that a vehicle with a pair of in-line wheels does not necessarily
do the obvious and fall over.  [laufmaschine - running cycle].
[This design] has no natural forerunners.

[Wonders about the forerunner of the idea of a bicycle. Suggests that
rather than going down from four wheels (e.g. French
celerifere) to two, which would obviously appear unstable, the evolution may
have been that of adding a wheel the wheelbarrow which has been around a long
time].
[Leonardo's drawing showing something like two wheels may have been something
quite diifferent; he was more "a draughtsman than a tinkerer"]

1 The (human) engine

[Human beings and IC engines both consume fuel and rely on oxygen to "burn"
it and convert it into useful energy and surplus heat.]
Both work at remarkably similar levels of efficiency, with some 30% ending up
propelling our respective vehicles. 16  
    [steam engines run equally efficiently at different RPMs, not so IC or humans]
IC engines need to be running nearly flat out to achieve these efficiency
figures; we clever apes still do quite well even on tick-over.

The energy ends up in the muscles, which can do only one thing. They can
shorten momentarily when signalled to do so by the brain.  But the fibers
cannot sustain this contraction, so sustained force is generated by firing
individual fibers in a sequence.  That is why we can punch harder than we can
push.  [? jerk > pull in weight lifting?]

White muscles produce most of our short
term sprnting or 'anaerobic' energy.  Mostly uses energy stored in the fibers
themselves - generally used for seconds, but can be sustained a few minutes.

The dark 'aerobic' fibers are the ones we use for continuous effort.  rely on
blood to replenish chemicals constantly, ultimately relying on the heart and
lungs for this flow.  Ratio of white and dark is mainly genetic, though
training can affect it.

Muscle tissue (both types) work best in a cyclic manner - contracted and then
relaxed and allowed to recover at short even intervals rather than trying to
exert a constant pressure.  The transfer of chemicals from the blood is a lot
easier when the muscle is relaxed.

Pedalling Cadence

The magic number [in the 1970s] was 100 rpm.   Some 25 years and a lot of
research later I see no reason to argue with this figure.  For a rider of
average height and build interested in maximum power output over short to
medium distance, 100 rpm is close to the optimum.

However, in track racing, for some reason, everyone gears down [no hills, no
wind].  Some athletes use a larger gear (Obree:110").  18

Table: Pedalling speeds

Power output (0.05-0.4hp): can be upto 1.6 hp for 11 seconds to about
   1 hp for 1 minute.  Road racers can put out a sustained output of about
   0.6 hp or 460W for 1hr (Eddy Merckx) or 0.5hp (4h).  For Most of us it's
   about 75-100W or 0.1hp (10-12mph) - 0.2hp (16mph).  More athletic types
   may manage upto 0.3hp sustained (18mph). 17
   Figure: Graph of power vs rpm, p.18 :
	0.4hp - about 10sec - max power at 100rpm
   	0.2hp - about 30sec - max power at 80rpm
   	0.1hp - about 2min - max power at ~70rpm
   	0.05hp - indefinitely - max power at ~60rpm
   seems to suggest that 60rpm is ok for sustained power.  The figure cites
   no source nor the kind of subjects used in the study.  I presume these
   numbers apply to the average bicyclist, and not to top athletes as in
   earlier table. 

Cadence (100rpm): Spinning up is a better way of getting maximum
   power than pushing with higher force.  This is because over time, it is
   easier to refuel muscles that are not running near their limits.  
   What is the best cadence?  Open to much debate.  The best evidence
   suggests that our bodies are quite happy with 100 rpm and tolerant quite
   a bit on either side.  Time triallists stick to around this number.
   However, when it comes to track racing, people tend to use a higher rate
   (they gear down). 18
	For 1hr runs paced by motorcycles or trains, gearing is much larger,
	and speed may be as much as 76 miles over 1hr.  p.17

Ratio of power to rest:  relates to muscle contraction / relaxation
   time more than anything else. Attempts to increase productivity by
   using elaborate contraptions that utilize power for 180 degrees etc are
   motivated by the fact that the typical 
   stroke is only effective for about 60 degrees of the cycle, so we are
   idling for 120 degrees or 2/3d of the time.  But utilizing this 2/3ds
   may not be optimal for the human body, since it needs longer to refuel
   the muscles than to activate them.  This refuelling ratio is in fact,
   6:1.  Thus, the 60 degree cycle is pretty close to optimum.  18-19

   Using both arms and legs will not improve power output - runs into
   capacity limits for lungs / heart. 19
     (also, elliptic chainrings give no advantage due to higher torque arm)

Pedal pressures are 10-30 kg, a fraction of body weight.  Also, avoids shock
loads and sudden reversals, rather more benign than running or even walking. 19

Saddle shape: Matter of personal taste.  Wide saddles, comfortable for
upright posture, are not good for long rides; pedalling rubs less on narrower
saddles.  
    My only advice is that they should be thinner and harder the further and
    harder you plan to ride. 23

Error in figure: on p.91 showing the lighter weight obtained by tensioned
spokes (as opposed to compressed tri-spokes, say) - shows the tension as
arrows on the spokes below the hub; in fact it is the spokes above the axle
that are in tension.  The spokes below the hub are neutral.  p.91

Tyres

Solid tyres - terrible - a) throws away the suspension, b) higher rolling
friction, c) less grip on road. 161-2
   [It] will take away something you prob didn't know you had : your
   suspension.  ... You thought only mountain bikes had suspension - but you
   were wrong.  Any rigic bike can have anything upto 45mm of travel at each
   end.  And very efficient suspension - isolates frames from high freq
   vibrations that would dramatically reduce its life expectancy.  ... So
   resign yourself to the inevitable and carry a spare inner tube. 162

8 Testing rolling friction

Do-it-yourself instructions: 
a) inflate wheels to same psi
b) start without pedalling from top of gentle slope, mark start and end point
	(say six meters apart - results in ~ 30 sec rolling time)
c) see time at final point. 100

Generally thinner tyres, or smoother tyres (slicks) have lower resitstance
and best grip.  High pressure reduces rolling res; but above 100psi just
makes them stiffer. 102