How Do Cyclists Reach Super Fast Speeds?
Even though spoked wheels and pneumatic tyres were invented
in the 1880s, bicycle design hasn’t really changed a great deal in the time
since – at least, at face value. However, look closer and around a hundred
years of research or development has taken the humble bicycle from boneshaker
to a speed machine.
The
basics
A modern bicycle is still made up of a double diamond shaped
frame, two wheels with air-inflated tyres and a chain-based drivetrain – the
mechanism through which the whole system runs. Though we’ve stuck to the
basics, man and his machine have increased in speed from the 14.5 km per hour
reportedly achieved by Karl von Drais in 1817 to a mind-blowing 55km in a Tour
de France time trial nearly 200 years later.
The ability to improve speed on a bicycle comes down to two
fundamental factors: you either increase the power that propels the rider forwards
or you decrease the resistant forces that are holding that rider back.
The rider’s ability to produce power is generally down to
their physiology and biomechanics. The resistant forces that slow a cyclist are
mainly air resistance, total mass and any frictional losses, such as the
drivetrain or the rolling resistance of the wheels against the ground. If every
athlete has an equal chance of winning the challenge for engineers and
scientists then is to focus on the technology the cyclist uses to obtain a
competitive advantage.
The
trouble with air
It has been demonstrated that
once a cyclist travelling outdoors gets past speeds of 25 miles per hour,
around 90% of the force holding them back will be air resistance. But the
relationship between speed and air resistance is not a linear one. It can, for
example, take twice as much human power to ride a bicycle at 30 miles an hour
as it does at 20 miles an hour.
As a result, reducing air resistance has become a top priority
in professional cycling technology in recent times. At the London 2012 Olympic
Games, Team GB’s track riders were using bikes, helmets and clothing solely
designed to help contribute to the optimisation of each rider’s aerodynamics.
Team principal, David Brailsford, has referred to this process as the
“aggregation of marginal gains”.
To achieve this, wind tunnels are now used by both
professional and amateur athletes to analyse the aerodynamic drag, then work
out how to get the rider and machine working together optimally. There is a
complication in this process, though, in that the best aerodynamic solution is
typically specific to every rider, so each needs to make individual choices
about their helmet and bicycle and especially their riding position.
The second problem is that wind tunnels are few and far
between and are by no means cheap to access. Thankfully, alternatives for those
without an Olympic-sized budget are emerging. You can now use computational
fluid dynamic software which can be, in essence, a virtual wind tunnel. This
software allows an engineer to simulate a variety of air flow conditions on a
new bicycle design, therefore cutting down the time and costs of prototyping
and testing. There is now also
published research which allows riders to assess their aerodynamics out in
the field rather than in a wind tunnel.
Mark Cavendish famously
won his Tour de France world title in 2011 wearing a skin suit and an
aerodynamic helmet while the majority of his competitors were still wearing
baggier jerseys and heavily vented helmets. Team GB had realised that even
though a rider may be sheltered by 200 others during a road stage, when
Cavendish sprints for the finish line, he is alone in undisturbed air for
around 200 metres at speeds well above 40 miles an hour. Every small advantage
at this point converts into winning millimetres.
Tinkering
with the tech
Racing bicycles themselves have been subject to a tremendous
amount of aerodynamic refinement over the last five years. Braking systems have
been positioned so as to be sheltered from the main airflow and gear cables are
now run on the inside of the frame. Wheel designs have not only improved in
reducing aerodynamic drag, but are now being optimised to provide benefits such
as increased rider stability from crosswinds. Innovations like these have
traditionally been directed towards making better bikes for either time trials
or triathlons but is now spreading towards the road bikes used in mass start
racing.
The mechanical properties of the racing bicycle have also
evolved. Like computational fluid dynamic software, finite element analysis
allows us to optimise the design of bike components to simulate the stresses
and strains that they will face when in use. This has allowed us to develop
composite frames that weigh as little as 800g but are still stiff enough to
sprint for a stage win and comfortable enough to be ridden for five hours or
more, day after day.
Even the humble gear derailleur, relatively unchanged in
principle since its original invention in 1951 has lately begun to shape shift.
The most advanced systems are now electronically powered and triggered. This
has allowed for smooth gear changes requiring only thin wires and a small
battery as opposed to having a frame design compromised by the limitations of
needing cable runs for mechanically actuated gears.
All these improvements have enabled us to morph the humble
bicycle into a speed machine without tampering with its basic design. So where
does this all lead next? In competitive sport, the technology is typically
regulated by its governing body. In the case of cycling, this means that the
equipment is currently limited in both its size, nature and weight, so we are
more likely to see more incremental improvements than a radical shift away from
the bikes we use now.
The average leisure cyclist is not limited by such
constraints allowing us to benefit from any level of innovation. For example,
if you look at bicycle land-speed records, recumbent cycles – which are unique
in the way they position the rider lying down – can move at far higher speeds
than a conventional bicycle. And for enthusiastic amateurs, new bicycle designs
are continuing to become lighter, faster and ultimately more efficient. Anything
could happen.