Designing the World's Fastest Bikes
Meera:: This is a special edition of the Naked Scientists with me, Meera Senthilingam. As this week, we're exploring the science and technology behind the Tour de France. Endurance events like this one rely on strong, sturdy, yet fast equipment to win points, time and stages. So the structure and design of these road bikes is constantly developing. To find out more about their design, I went along to the warehouse of Trek Bikes, providers to team RadioShack on the tour, and met media officer and avid cyclist, Chris Garrison.
Chris - Bicycles basically have the same shape, no matter what they're made from. You'll have basic things, like the shape of the handle bars will either be flat or they might be Ram's horns, which are road bike bars. What you really need to look at is what the bike is made out of. Is it a metal bike or is it something else - a "composite material" we say. The highest end bikes are going to be made entirely of carbon fibre. Most other bikes, the common bikes that you see on the street, are either made from steel or aluminium. The real difference between one bike and another is what it's made from.
Meera - Chris, we're currently in the middle of the Trek warehouse. We're surrounded by thousands of very expensive bikes, but we have one particular model here in front of us which is a typical one of your high end road race bikes. Tell me more about its structure.
Chris - This particular bike is our flagship model. It's called the Madone. The thing that's going to separate one Madone versus another is the type of carbon fibre blend that we put into the bike. Carbon fibre is a lot like paper; You have something like lace paper that's really thin, you have normal everyday A4 paper - then you can go all the way up to a carbon fibre that's more like cardboard. It's thicker, it weighs more, it's a little bit structurally more sound. The highest end Madones are going to have the most lightweight carbon fibre within them, and we're going to use the heavier weight carbon in places where we need the bike to be very, very structurally strong and stiff.
Meera - But what aspects of it are made of carbon fibre? I know the frames are, but interestingly so are the wheels - so it's all just carbon fibre here.
Chris - If you imagine what a typical bicycle looks like, you essentially have two triangles that are attached to each other in the middle. In this case, everything in those two triangles on this bike are made of carbon fibre. Also, the part that holds on the front wheel of the bike (which is referred to as the fork) is made of carbon fibre, and in this version, the wheels themselves, the rims, the actual breaking surfaces are also carbon fibre, and then there is a carbon fibre fairing which helps in the aerodynamic proportion of the wheel - that is also made of carbon fibre. So the whole bike from tip to tail, with the exception of the saddle and the things that you actually grip onto with your hands, is made of carbon fibre. The frame itself is not all one piece of carbon, but rather, it's several pieces of the carbon that have been molded individually, and then are pieced together like a giant jigsaw puzzle, and held in place with a space age level epoxy that we borrowed from NASA.
Meera - And how much of a difference does this make in terms of performance of the bike?
Chris - Carbon fibre is light and fast. If you have someone who is a top level rider like a Lance Armstrong, then when they actually need to put a lot of power into the bike, the material itself is going to maintain its shape. It's not going to deflect. It's not going to be like an aluminium can that you can bend and then eventually break apart. It's going to maintain its stiffness and the reason why it's able to do that is because of the forces that carbon fibre is able to take. It's extremely, extremely strong under compressive load, which is the same thing as standing up out of the saddle and putting power into the pedals. You don't want the bike to flex in that situation because then it means that the rider is actually wasting energy in order to make the bike go forward.
Meera - But now moving away from the material itself and onto other aspects of the bike, how about the gears? Bikes like this, how many gears do they typically have?
Chris - Most bikes will come with 8, 9, or 10 gears in the back, and either two or three chain rings in the front.
Meera - And typically say, a rider in the Tour de France - so one of their bikes.. how many gears or what gear combinations would that have?
Chris - They'll definitely have two chain rings in the front. Usually, it is one large chain ring and one smaller chain ring. The larger one, they'll use for flats and for descent, one enormous one if they're doing a flat time trial for example, and then either 10 or 11 speeds in the back. Again, it depends on what the terrain is of the day. If somebody is racing in the tour, then they're going to mix the gear combinations depending on what stage they're riding. If they're in a flat stage, then they're going to have harder gears in the back because they don't need climbing gears. If it's a day where they're spending the day entirely in the Alps or the Pyrenees, then their mechanics are going to put a different gear set on their wheels that make it easier to climb those big, enormous hills. At the same time, they'll keep the chain rings in the front probably the same as they are ,because there's going to be a descent at some point, where they really want to drop into those hard gears and start building up lots and lots of speed in the descent.
Meera - So that's quite handy that they just change it along the tour itself?
Chris - They have a service truck with spare bikes, spare wheels, spare saddles, spare handle bars, spare everything.
Meera - Now this particular bike though has electronic gears which is a fairly recent technology in terms of bike. So, how does this actually work electronically and how much of a difference does it make?
Chris - At the end of the day, you have a derailleur in the back that moves the chain from one gear to another, and you have a derailleur in the front that does the same thing. What is different about it though is that it's now done by wire instead of by a cable, and as a result of that, the shifting of this bike is extremely, extremely smooth, over say, a cable actuated set up. It also means that the front derailleur knows which gear the rear derailleur is in, and it can adjust itself accordingly, so that you'd get away from that really annoying chain rub that you often hear when you're riding a cabled system. The weight is really no different than its non-electrical counterpart. It has a battery that adds about 58 grams to the overall weight of the groupset, but otherwise, it's kind of one of those things that is pretty cool in terms of the bells and whistles additive to the bike.
Meera - But one thing I mainly notice when looking at professional road bikes like these ones, is just how thin it is. So the wheels themselves look like they're about an inch wide or so.
Chris - They actually run somewhere between 18 to about 27 millimetres wide, entire width. Typically, what the pros will ride on is probably in the 23-millimetre neighbourhood, and all of that is just designed to reduce the amount of drag that they're experiencing as they go over the road. It's not like a mountain bike where you want to have a thicker tread because you're going over surfaces that aren't paved. In this case, these guys are riding on tarmac roads all the time. They don't need a large contact patch. They want to go fast and the larger the contact patch, obviously, the more drag is going to be on the bike, and that means they're going to go slower.
Meera - Chris Garrison from Trek Bikes.