Science / Medicine : Mechanical Engineer Goes ‘Backward’ to Learn About Bikes

At first glance, Richard Klein’s “backward” bicycle looks normal. Then you notice that the positions of the seat and the handlebars have been interchanged so that the bike steers through the rear wheel rather than the front.

But that seemingly minor change makes a major difference, the University of Illinois mechanical engineer said: The bike is unridable. “It’s just impossible. . . . Everything you do is wrong. Too many things go bad on you at once.”

Klein, 49, did not set out to build an unridable bicycle. The backward bike is just one of more than a dozen highly unusual bicycles built by students in his sophomore physics course to explore the dynamics of moving machinery.

And in the process Klein and his students have learned a great deal about the fundamental laws that govern the mechanics of the bicycle, overturning some notions long cherished by physicists--as well as science fiction writers--and opening new questions for discussion.

They have also had a lot of fun and have even developed some ideas with commercial implications. Klein claims, for example, that he can teach a young child to ride a bicycle in two minutes flat.

One long-held notion of engineers is that bicycle riding is made possible by the gyroscopic effect of the wheels. Anyone who has ever held the axle of a bicycle wheel while the wheel is spinning knows that the wheel strongly resists any twisting motion of the axis.

This gyroscopic effect was long used in navigational devices before satellite navigation generally superseded it. And many engineers believe the gyroscopic effect of the bicycle wheels keeps the bike upright. Not so, Klein said.

Klein’s students have made several “zero-gyroscopic” bicycles by mounting a second set of identical wheels above the bike’s original wheels, but rotating in the opposite direction so that the gyroscopic effect of the original wheels is canceled out. The bike is eminently ridable, Klein said.

“When other scientists argue about the importance of the gyroscopic effect, we simply invite them over to ride one of the bikes,” he said. “That changes their mind.”

But he concedes that the zero-gyroscopic bicycle cannot be ridden no-handed, so the gyroscopic effect does contribute greatly to stability of the bicycle.

What then does make a bicycle ridable? Klein believes the major answer lies in the angle of the front fork. Klein’s students built what he terms a “naive” bicycle in which the front wheel contacts the ground directly under the handlebars. This bike “is much less stable than a regular bike,” he said, although it can be ridden. But like the zero-gyroscopic bike, it cannot be ridden no-handed.

Optimum ridability occurs, Klein and his students have found, when the bike’s head--the hollow tube below the handle bars through which the fork is mounted--is attached to the frame at an angle of about 20 degrees from vertical.

“That’s the easiest bike to ride no-handed. Not surprisingly, that’s the angle most manufacturers have adopted” through a trial-and-error process, he said.

And the science-fiction aspect? Many science fiction authors have concluded that a pollution-free bicycle would provide an ideal form of transportation in an orbiting city or in enclosed cities on low-gravity worlds like the moon. Again, Klein says not so.

His students have not ridden bicycles in low gravity. But they have put together computer programs that predict what will happen. The physics show that in low-gravity environments it is necessary to lean much more when making a turn--perhaps 50 to 60 degrees instead of the normal 5 to 10 degrees. But because of the low gravity, the friction between the wheel and the ground is much lower and the bike would slip out from under the rider. The low friction would also make it extremely difficult to stop.

“Perhaps it would work if you rode on a Velcro surface,” he suggested.