User Guide

10
11
29 INCH WHEELS
Bicycle wheel size changes
Why are bicycle wheels the size they are?
The first machine considered a true bicycle
was called a Draisienne, after the German
credited with inventing it. This embryonic
bicycle allowed the rider to sit between two
wheels, glide and steer. The propulsion was
provided by pushing along the ground with
one’s feet. Limited by the length of a man’s
legs, the wheels were not overly large, and
the rider sat near the ground. The Draisienne
set speed records during its day, and was
a highly efficient form of locomotion at the
time.
For the purposes of this discussion, the
next step in bicycle development was increas-
ing its speed by attaching pedal cranks. The
easiest method for attaching pedals was to
put them directly on the front wheel axle,
like modern tricycles. This put the pedals in
front of the rider, for both comfort and ease
of use. While pedaling increased the speed
of the bike, it quickly became apparent that
a larger drive wheel would make for further
increases. As the front wheel grew, the rear
wheel became smaller to reduce weight and
maintain the handling characteristics of a
shorter wheelbase. To maintain control over
the bike, the rider had to sit near the steering
axis, necessarily above the wheel. This new
design was known as the penny-farthing, or
Ordinary.
As the size of the drive wheel grew,
bicycle speeds increased. Wheels got big-
ger and bigger. The riders on these bigger
wheels got higher and higher off the
ground (Fig. A1). Crashes became common.
Remember, paved roads at that time were
rare. Special handlebar designs were devel-
oped to make it easier to dismount as the
rider flew over
the front wheel.
Even with the
many crashes,
wheel size
increased. The
limit on wheel size
was the rider’s leg
length. If the
wheel was too big,
the rider simply
could not reach
the pedals. Still,
riders wanted
more speed.
Several solutions were put forth, and the one
that succeeded was a chain-driven rear wheel.
With the introduction of chain drive, bicycles
acquired gears and gear ratios. By using cogs
attached to the cranks and rear wheel, with
different numbers of teeth, a single turn of
the cranks could mean multiple turns of the
rear wheel. This allowed a bicycle with small-
er wheels to travel greater distances with a
single revolution of the cranks. It also put the
rider as close to the ground as pedal clear-
ance would allow, and with two wheels of the
same size. With the lowered center of gravity
or these bikes, their riders weren’t nearly as
prone to pitching over the front wheel, and
thus the new bikes became known as “Safety”
bikes.
The wheels used on early Safety bikes were
made of iron, steel or wood, which were then
covered with a variety of materials. None of
these cover materials was particularly shock
absorptive, nor much help in achieving trac-
tion. However, they allowed a bike design
to utilize whatever wheel size its creator
desired. This was a time of experimentation,
and wheel size varied a great deal. Some
bikes had similar wheel diameters, others
had different front and rear wheel diameters,
and there was even disagreement on which
end of the bike got the bigger wheel.
One of the next significant development in
bicycle technology was pneumatic tires. This
truly was a revolution, allowing bikes to float
over small bumps, maintain traction, and all
with a great deal more comfort. Soon after
their introduction, pneumatic tires became
a requirement for any performance bicycle.
Tires, then, are what finally settled the
debate of wheel size. Wheels were thereafter
made in sizes to fit the tires available at the
time.
A brief review of the literature did not
reveal any specific reason why specific sizes
were selected. Instead, its probably a function
of tires being made to fit an existing wheel.
And that wheel size was determined to fit
within the existing bicycle design parameters
as they occurred at the time.
Later, a similar choice was made at the
birth of the modern mountain bike. When
pioneers like Gary Fisher were building their
clunkers for the famous descent of Mt.. Tam,
the available tire size in a balloon tire was
26”. Gary chose his rim size to fit the tires
which he believed would work the best. As
Fig. A1
Center of
gravity
Pivot