As the Tour de France enters Paris this weekend, an increasing number of amateur cyclists are stretching their legs on two wheels, and stretching their Lycra as they do so. The resurgence in the popularity of cycling in many countries is a twenty-first-century success story, and one that offers some hope as the world searches for sustainable cities and transport systems.
Still, as we discuss in a News Feature this week, despite advances in materials and technology (and an obsession with shedding weight), the geometry of a bicycle frame this year looks, to a physicist at least, pretty much the same as last year, and as it almost always has.
Where is the innovation? The Ford Motor Company has patented an inflatable bicycle frame, although (not surprisingly) the invention tries more to tackle the problem of how a bicycle can be transported, say in the boot of a car, than how it can be ridden.
For raw speed, enthusiasts should head not to the peaks of France, but to Battle Mountain, Nevada, this September. On a 200-metre run of State Route 305 (closed to traffic), cyclists will compete to break the human-powered land-speed record. The annual event draws engineers and riders from across the globe, to roll machines that look from a distance like eggs along one of the world’s straightest, flattest and smoothest roads. The current record is just under 135 kilometres per hour.
The frames of these speed machines do look different from your standard racer. For better aerodynamics, they are recumbent bicycles (prone bikes, on which the rider lies chest down, have also been built). And this is where the physics of cycling does have an important role — some teams are experimenting with rear-wheel steering, which offers a shorter, and so more efficient, chain.
Rear-wheel steering is less stable than front-wheel. Yet, as most people who have got upright on two wheels will recognize, bicycles in general are more stable than they look to non-riders and learners. Given a push, most will even stay upright without a rider. Sometimes, it takes a person trying to control a bike to make it fall over.
The majority of times that a rider and bike do fall over and cause injury, there is no one else involved. And often the problems come at the start or end of the journey, or when a rider is forced to stop en route — especially for older people. A paper this year in Safety Science found that 20% of injuries to older cyclists come when the riders are trying to get on or off (R. Dubbeldam et al. Safety Sci. http://doi.org/bmqf; 2016). This is where science can help. The study analysed the mounting and dismounting strategies of cyclists young and old, and saw that older people — perhaps because of how they were taught — tend to begin and brake with one foot hopping along the ground as the wheels turn, which is less stable than starting or stopping with both feet on the pedals. You never forget how to ride a bike. But some people need a refresher.
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