The science of faster bicycles
This week marks 5 years since the Olympic games kicked off in London -during which the incredible cycling team won a total of 8 gold medals. British riders are still going strong - as demonstrated by Chris Froome’s recent victory in the Tour de France for the third time in a row. But it’s not all down to the riders, there’s some serious science behind the bikes as Tom Crawford has been finding out. But first, a flashback to five years ago…
Announcer - Round the back and for one final time I think he’s going to do it. Chris Hoy claims the gold medal. What a moment in British Olympic history… a record sixth gold medal here, now at London 2012. Get on your feet for the knight of cycling. Sir Chris Hoy is in uncharted waters now…
Tom - It still gives me goosebumps even now. Not content with just reminiscing, I went along to this summer’s Royal Society exhibition to meet Professor Stuart Burgess. He’s an engineer who worked on the actual bikes used in the 2012 games and he had one to show me…
Stuart - It’s a track bike for going round the velodrome. The bike can go up to 50 miles per hour so it’s highly optimised for speed throughout the whole bike. At Bristol University, we’ve worked on the chain drive - that’s the chain, sprocket, and front chainwheel to reduce the losses in the drive to maximise the efficiency as much as possible to help the bike go as fast as possible.
Tom - So this is a case of British cycling recruiting academics like yourself to be like - guys can you please help us go faster using science?
Stuart - Yeah. Cycling is a really interesting sport because the bicycle has to suit the rider. It’s not like javelin, or shot putt where everyone has the same equipment and, therefore, there’s a lot of engineering science that goes into the bike. When a team like Team GB win a medal, it’s not just the riders - they are the most important part - but it’s also a reflection on the design of the bike as well.
Tom - What kind of things then would be incorporated into a bike design for, just in general, in terms of going faster and also in terms of a specific rader?
Stuart - Well, the aerodynamics are the most important for a bike. When a bike’s going 50 miles and hour, the aerodynamics of the rider are very important, so he leans right down. His clothing equipment is really important, they wear those skin tight suits but, also, the transmission is important. Even though the chain and the sprockets are a small part of the whole system it’s important to minimize the losses in those components and, so at Bristol University, we’ve done a lot of of testing. Testing of all kinds of lubricants, coatings, materials, sprockets to see which ones are the most smooth and the most efficient.
Tom - I’m a mathematician, and I notice you have a lovely looking equation on your display here. Could we possibly just go and have a quick look and you talk me a little bit through that?
Stuart - Basically we’ve got the drag equation for a bicycle. So, on the one side you have the power output of the rider, which is pretty phenomenal for these olympic riders, and on the right hand side you have the various contributions to drag. So you have the aerodynamic drag, you also have the rolling resistance of the tyres, you also have an acceleration term, but you also have an efficiency term for the efficiency of the transmission.
The reason for having that equation up there is to show the general public that engineers use maths and science to design a faster bike. Because, when you look at the equation, you can then see which are the important parameters. You see that maths is an important parameter, drag coefficient is an important parameter, the rolling resistance of the tyres is an important parameter. So an engineer looks at those and then says well I need to minimise certain parameters like the mass and the drag coefficient, and I need to maximise certain parameters like the transmission efficiency. So maths is very important to an engineer.
Tom - Just when you said the power output is phenomenal for an olympic rider, could you give me a comparison or just some idea of how powerful these athletes are?
Stuart - Well, when a commuter’s cycling to work that would typically be 60/70 watts. But when some of these sprinters are going round the track, sometimes it can be 1½ kilowatts of power. So it’s an incredible amount of power, and the torque they’re putting into the crank and chain is really very high.
Tom - I imagine you have to make sure these things are also designed to be able to withstand that level of power and torque?
Stuart - Yeah. That’s the great challenge because, on one hand, you need very lightweight components so you use carbon fibre and the bike itself weighs 6.8 kilogrammes so it’s a very lightweight bike. But, on the other hand, you have some of the most powerful, strong athletes in the world who are going to exert great forces on this bike so you have to make it strong at the same time, and that’s the great challenge of engineering.
Tom - Just finally, will this kind of technology make it’s way into consumer bikes?
Stuart - Yeah. That’s a question that we’ve been answering during the week. Yeah, after a couple of years this technology drips down to club cycling etc. But not only that, we’re hoping we can spin off some of the technology onto other chain drives in factories to make factories more efficient. So it’s not just about the olympics, we want this to have a benefit for society.