Sports tech: Cycling
To win the Tour de France a cyclist relies on a highly engineered road racing machine.
At its heart a bike is a fairly simple engineering enterprise: a frame for support, two wheels for traction, direct drive gears and chain for power, and handlebars to steer. But when it comes to professional road racing, the complexity multiplies.
Although injury has prevented Sir Bradley Wiggins defending his 2012 Tour de France crown when the race begins on 29 June, Team Sky will still field a strong squad including Chris Froome. The Kenyan-born cyclist, who rides for Great Britain, claimed a bronze in the individual time trial at the London Olympics last year.
The highly engineered machines that Froome and his team mates will race over the 23 days, 3,360km and 21 stages of Le Tour, are as far away from the road bikes that cycle the roads of the UK as a Formula One car is from a Ford Focus.
Much like a Formula One car, a professional bike is the sum of all its parts; chassis, wheels, tyres and gears. The frames raced by Team Sky come from Italian manufacturer Pinarello: the Dogma 2 chassis for road racing and the Bolide for time trials.
The Dogma 2 is the latest evolution of Pinarello's road racing bikes, taking over from the Dogma 60.1, which introduced the asymmetrical frame design. The thinking is simple. A bike is not symmetrical; the transmission is on the right hand side of a frame. Therefore the frame should be stronger and stiffer to handle chain forces on the side where they are greatest.
Using finite element analysis and lab testing Pinarello studied the forces acting on each side of the frame. The design of the Dogma 60.1 reflected this research with tube shapes and carbon fibre lay-up tailored to handle the forces acting on the frame.
The result for the 60.1 was different on the left and right chainstays, with more material where the right stay meets the bottom bracket, and a beefier tube toward the left-hand rear dropout. The top tube is shaped differently on each side, and the right fork leg is bigger than the left.
For the Dogma 2, this has been taken further with some additional changes made to improve stiffness and aerodynamics while saving 30g over the original Dogma. The biggest change is the new fork and head tube, which now uses a 1.5in lower bearing instead of the previous 1.25in. Increasing the size of the bearing means the steerer and head tube are bigger and therefore stiffer. That improves handling in corners and in straight line sprints, as well as making the front end stiffer against braking forces.
A completely new fork slips into the new larger head tube. The Onda 2 fork is more aerodynamic than the original Onda. It has a shaped crown, which fits into the down tube to improve airflow to the frame. Moving backwards along the frame, the down tube has been reshaped for improved aerodynamics and is asymmetrically shaped, while the top tube is slightly off-centre in a further development of the asymmetric design concept.
Internal routing for gear cables or wiring is a further aerodynamic improvement on the Dogma 2.
For the time trials Team Sky will use the recently launched Bolide. In his victorious 2012 campaign Wiggins rode its predecessor, the Graal. Technicians went as far as to investigate the impact of air flow on every single component, reducing the total aerodynamic impact by 15 per cent compared to the Graal.
Aerodynamic improvements include the use of new airfoil tube sections and profiles designed to ensure the lowest aerodynamic resistance in all wind conditions to generate a forward thrust. In addition, the use of a concave back on the seat tube allows a closer position of the rear wheel, significantly improving the air flow in that area.
Complete integration of the brakes to hide them from the air flow greatly reduces aerodynamic resistance, while internal cable routing optimises the interaction between the airfoils and the air flow.
An integrated handlebar gives a unique continuity with the frame and greatly reduces the resistance, compared to a traditional stem and bar.
For the gear set, Team Sky will use Dura-Ace 9000 from Shimano. Riders have been using the electronic-shifting Di2 version designated 9070, on which there are several significant improvements as well as the overall mechanical bonuses, not least being a smaller battery hidden away in the seat tube.
The headline feature is the 11 sprockets on the rear wheel, but according to Dura-Ace engineer Takao Harada, the objective was to achieve more than just an extra gear ratio to choose from. "Every component is completely redesigned to achieve an overall lighter weight for the mechanical version under 2,000g, while improving the feel and shift precision of the gears; especially the front mechanism, improved modulation and mounting options for the brakes," he says.
The fab four: The elements of the professional racing bike
The frame is the structure that supports all other components. The term frameset sums up the combination of frame and fork, which are connected by a steering bearing - the headset - so they work together and are often designed to match both visually and mechanically.
A bike's largest single part, the frame supports the rider and provides attachment points for the other components. It is light so that as little as possible of the rider's effort is used in propelling the bike, and stiff so that energy is not wasted in flex.
The frame's design, construction and materials determine how the bike rides and handles. Bike manufacturers spend a lot of time and money designing and developing their frames.
Most high-performance frames today are made from carbon fibre. The advantage of this is that it can be tailored to the loads on each part of the frame. This efficiency and high strength result in very light frames. The bare frame of one of Team Sky's Pinarello Dogma 2 bikes - made from Torayca carbon fibre - weighs just 920g.
Bike wheels are so common that few of us ever stop to think how remarkable they are. A pair of wheels that weighs under 1,500g can carry a bike and rider that weighs over 100kg and will withstand loads many times greater if, for example, the rider hits a pothole.
The key to the success of the wheel is the tension in the spokes. For millennia all wheels worked by supporting the hub by pressing down on the spoke. Engineer George Cayley invented the much lighter wire-spoked wheel in 1808; its first widespread, practical use was on early Ordinary ('penny-farthing') bicycles of the 1870s.
When you sit on a bike, the tension in the spokes between the hub and rim is reduced. This is equivalent to compressing a wooden spoke, but because a metal spoke is far stronger the wheel can be much lighter.
Modern rims come in two types: clincher and tubular. The choice for races is tubular tyres. These don't have a hook as the tyres are glued into place, making the rim and tyre lighter as a result. It's also possible to ride a well-glued tubular tyre when it's completely flat.
The tensioned wires connecting the hub and rim are usually made from stainless steel. Lightweight wheels may use aluminium or even carbon fibre, but when strength and reliability are paramount, in events such as the punishing Paris-Roubaix classic, most racing teams use tried and tested steel-spoked wheels. Spokes may be thicker at the ends than in the middle to save weight and, by distributing the loads round more of the rim, make the wheel stronger.
Almost all racing wheels are held in the frame with a quick release skewer. The wheel can be removed by simply flipping the lever, so if the rider needs a replacement he can be back on the road in seconds.
Racing cyclists put an amazing amount of faith in their tyres. After all, they are in contact with the road through just a couple of square centimetres of rubber even as they zoom down mountain passes at 100 km/h.
The rubber strip on the outside of the tyre provides grip. Tread is made from various rubber compounds and blends, usually with carbon black or silica added to improve grip and durability.
The body of the tyre is made of layers of fine nylon, cotton or silk threads. The casing holds it together against the pressure of the air in the inner tube. The fineness of the casing is usually expressed in a high number of threads per inch. A high number indicates a more flexible casing with lower rolling resistance (the amount of effort that pushes the tyre along the road).
Tubular tyres are a single doughnut-shaped piece with the carcass sewn together around the inner tube, and the stitching covered by a tape. Glue is applied to this tape and to the rim to join them. They are slightly lighter than clinchers and a properly glued tubular can be ridden while flat for a while if necessary, so a racer can continue riding while waiting for a support vehicle.
Humans are lousy vehicle engines. Even the fittest can only generate a few hundred watts for any length of time - that's about half a horsepower. Our legs, hearts and lungs work best in a fairly small range of speeds and motions.
Bike gear ratios are expressed in 'gear inches' in the English-speaking world, and in 'development' or 'rollout' elsewhere. Rollout is straightforward; it's the distance in metres the bike travels for one turn on the pedals.
On a typical road racing bike, the highest gear comes from a 53-tooth front sprocket or chainwheel and an 11-tooth rear sprocket. That gives a rollout of 10.4m and a 130in gear. A typical low gear with a 39-tooth chainring and a 25-tooth sprocket gives a rollout of 3.4m or a 42in gear. Most modern gear systems are based on the derailleur - a mechanism that moves the chain between sprockets of different sizes.
To shift gears most bikes have two derailleurs, operating on the chainrings and the rear sprockets. Controls on or near the handlebars pull cables to actuate the derailleurs.
The rear derailleur uses a pivoting parallelogram mechanism and pulley wheels to lift the chain between sprockets. The front derailleur is cruder, using metal plates to shove the chain around.
The latest derailleur systems are powered by batteries and use motors. By eliminating human error, electronic shifting delivers almost-infallible, extremely quick gear changes.
In recent years the formerly little-regarded hub gear has made a comeback. Hub gears have a system of cogs called an epicyclic gear inside the rear hub, and are reliable because the mechanism is enclosed. Friction between the cogs means these gears are less efficient than external systems.
|To start a discussion topic about this article, please log in or register.|
"What the Scottish independence referenda could mean for engineers and engineering on both sides of the border"
- What to Specialise in Electronics Engineering?? [03:02 am 03/04/14]
- Britain to have just one remaining coal pit by the end of 2015 [01:11 am 03/04/14]
- LV Generator Star point earthing - UK [08:35 pm 02/04/14]
- East West Rail - the Oxford to Bedford route [07:33 pm 02/04/14]
- Small nuclear power [06:06 pm 02/04/14]
The essential source of engineering products and suppliers.
Tune into our latest podcast