At the museum we have a great exhibit with two racing bikes along a simulated course; this has sparked a range of questions on the topic of cycling, from the physics of riding a bike to the most popular question;
how can we cycle faster?
How do we master the art of balancing on two wheels?
Of course in order to ride a bike quickly, we must master riding a bike slowly. You may have wondered why it is so difficult it is to keep the bike upright when stationary or going very slowly, but this becomes much easier as soon as you start to pick up speed.
Almost everyone can ride a bicycle, yet apparently no one knows how they do it.
(Jones, D. 1970)
The first theory proposed is that the bike is able to stay upright due to the skill of the rider. For example, if the rider feels the bike falling to the left, they turn the handlebars to the left so the bike begins to move along a circular path. This generates a centrifugal force that pushes the bike and the rider back upright.
As the bike picks up speed, the front wheel starts to act like a gyroscope which helps even more. The video below has some nice explanations of bike balance:
Now we’ve got the bike moving the next stage is to keep the bike going at speed. Cycling is known for being an efficient mode of transport but there are a number of forces trying to slow us down as we pedal, and these forces can get bigger as you go faster. The main contributors are:
1. Mechanical resistance
2. Rolling resistance
3. Aerodynamic resistance
The force from mechanical resistance comes from friction as the chain and other parts of the bike move. A badly maintained bike has high mechanical resistance so make sure your bike is oiled and greased regularly.
Rolling resistance is a result of the friction between the tyres and the road. High pressure tyres have a lower rolling resistance because they deform less as they roll. If you want to go fast, keep your tyres pumped up!
As cyclists, we want to try and reduce this drag force. We don’t have any control over the density of the air, but by trying to reduce our frontal area and drag coefficient we can start to cycle faster! One key way to do this is using a technique called drafting. A great example where drafting can be seen in action is in the team pursuit event in track cycling.
Team pursuit cycling event (Image courtesy of Arc_of_Marc, Flikr)
What is the science behind drafting?
As the air flows over the front cyclist it becomes disturbed and chaotic (turbulent). The air behind the first cyclist drops in pressure and density and begins to change direction . All of these effects mean that the second cyclist has a much easier job, they only have to create about 70% of the force of the first cyclist in order to travel at the same speed. This is why cyclists will often take turns at the front of a group in order to share the effort. The video below shows the British team working together to win a gold medal at the Track Cycling World Cup
Another effective way to reduce our drag force is to change our position when we ride. The human body is not very streamlined, so your position on the bike plays a very important role.
Graeme Obree’s crouch position was used to break world records.
Next time you are out cycling with a friend; See if you can feel the difference when cycling behind compared to taking the lead. See if you notice the difference sitting upright to crouching down in race position.
How fast can we go?
The fastest cycling record (on a production bike) was set on a mountain bike in 2007 by Markus Stöckl. He descended the snow covered ski slope of La Parva in Chile on an Intense M6 mountain bike setting the record of 130.7 mph (210.4 kph)!
The fastest human powered vehicle record was set by Sam Whittingham in 2009, reaching 83 mph (133 kph) along the flat. Sam was riding a recumbent style bike where the pedals are positioned out in front of the rider, helping reduce the frontal area, lowering the effect of the drag force. The video below has some great description of the bike he used and the science behind it.
The fastest a human has ever travelled on a bike is 167 mph (268 kph); this was set by Fred Rompelberg in 1995. This speed was achieved by using the principle of drafting we discussed above, Rompelberg was initially pulled along by a dragster and then when released, used the wake created by the dragster to lower his drag force and reach that record speed (video below is subtitled)
To answer the question, how fast will we be able to go on a bike, is tricky. Perhaps combining all the techniques above together (drafting, low frontal area and gravity assisted) the 200 mph mark may one day be achievable!
Example of a recumbent bicycle designed for high speed. (Image courtesy of Greg Kolodziejzyk, Flikr)