Daily News Digest

by Mark Zalewski

July 22, 2016

In today’s CyclingTips Daily News Digest: Froome beats Dumoulin to win Tour de France TT as podium battle tightens; Rivera wins final stage as Cecchini claims overall at Internationale Thüringen Rundfahrt; Gidich takes second stage win at Tour of Qinghai Lake; BMC leadership questions answered: Porte seeks Tour de France podium, Van Garderen into support role; Stats and storytelling: how Dimension Data is breaking down the Tour de France; Froome in control, but behind, five riders in contention for podium finish in Paris; How Mark Cavendish got his Tour de France mojo back; Young cyclist talks about team pressures to dope; Tour de France Tech: The new FSA electronic groupset; Archbold suffered through crashing to finish Tour stage; A Day On The Side of The Road; Scientists take a fresh look at what makes a bike stable; Tour de France, stage 18 recap; Tour de France, stage 17 on-board highlights; Tour of Qinghai Lake, stage 4 highlights; Sondre Hols Enger ‘celebrates’ on the team bus; The absolutely most-epic mountain bike video ever!

Scientists take a fresh look at what makes a bike stable

by CyclingTips

While engineers and bike manufacturers use geometry and statistics to design their bikes, the science behind what makes a bicycle work is actually less understood. Scientific American features a resurgence in the study of the mathematics behind what makes a riderless bicycle stable.

Here is an excerpt from the feature:

The link between leaning and steering gives rise to the bicycle’s most curious feature: the way that it can balance while coasting on its own. Give a riderless bike a shove and it may wend and wobble, but it will usually recover its forward trajectory. In 1899, English mathematician Francis Whipple derived one of the earliest and most enduring mathematical models of a bicycle, which could be used to explore this self-stability. Whipple modelled the bicycle as four rigid objects—two wheels, a frame with the rider and the front fork with handlebars—all connected by two axles and a hinge that are acted upon by gravity.

Plugging the measurements of a particular bicycle into the model revealed its path during motion, like a frame-by-frame animation. An engineer could then use a technique called eigenvalue analysis to investigate the stability of the bicycle as one might do with an aeroplane design. In 1910, relying on such an analysis, the mathematicians Felix Klein and Fritz Noether along with the theoretical physicist Arnold Sommerfeld focused on the contribution of the gyroscopic effect—the tendency of a spinning wheel to resist tilting. Push a bicycle over to the left and the rapidly spinning front wheel will turn left, potentially keeping the bicycle upright.
In April 1970, chemist and popular-science writer David Jones demolished this theory in an article for Physics Today in which he described riding a series of theoretically unrideable bikes. One bike that Jones built had a counter-rotating wheel on its front end that would effectively cancel out the gyroscopic effect. But he had little problem riding it hands-free.

This discovery sent him hunting for another force that could be at play. He compared a bike’s front wheel to the casters on a shopping trolley, which turn to follow the direction of motion. A bicycle’s front wheel can act as a caster because the point at which the wheel contacts the ground typically sits anywhere from 5 centimetres to 10 centimetres behind the steering axis (see ‘What keeps a riderless bike upright?’). This distance is known as the trail. Jones discovered that a bike with too much trail was so stable that it was awkward to ride, whereas one with negative trail was a death trap and would send you tumbling the moment you released the handlebars.

Click through to read more at Scientific American.