

Braking & Steering Page: 3 of 3 Turning Point Activity

Making a turn on a bicycle is easy compared with explaining what you do to make a bicycle turn. Your position, the bicycle's position, and the position of the front wheel all make a difference. In our experiments with bicycles, the Exploratorium staff has discovered that you can initiate a turn to one side by steering to the other side. Motorcycle riders call this "counter-steering," a small jerk on the handlebars in one direction to initiate a turn in the opposite direction. Try it yourself. Ride your bike in a straight line through an open area where there is little traffic. When you are moving at a moderate speed, jerk your handlebars slightly to the right. Notice that your bicycle and body are thrown to the left, and you have to steer left to remain upright. When you ride a bike in a straight line, you must make many minor corrections in order to stay upright. Ron Hipschman, the author of this activity, demonstrates these corrections by riding along a length of white paper. The curving tracks show the path of Ron's front wheel as Ron steered his bike to the left to correct a fall to the left, then to the right to correct a fall to the right.

You can examine your bicycle's path by riding through a puddle to wet the tires, then making a sharp left turn. Look at your tracks, and notice that your front tire swings slightly to the right, then to the left. Ask a friend to make a sharp turn and watch his front wheel and handlebars as he does it. You may notice that he jerks the handlebars just slightly to the left before he turns right, and vice versa. At the Exploratorium, our experimentation has convinced us that you turn your wheel to the right to throw your weight to the left. To change direction, you need the help of a force outside of yourself and the bicycle. Trying to change direction without the help of an outside force is like trying to pull yourself up by your own shoelaces. It doesn't work. If you were to try to fling yourself to one side, you would go in one direction and your bike would go in the other, counterbalancing your weight shift. When you turn your front wheel to the right, your bike heads to the right, but your body tends to keep going straight. If you are traveling fast and you twist the wheel sharply, your momentum may cause you and your bicycle to part company when your bike turns and you continue in a straight course. If you turn the wheel less sharply, you still feel the effect of your forward momentum: you feel like you are thrown to the left. An outside observer, like the one who drew the sketch below, would see that the push to the left is really just your tendency to continue on a straight course, interrupted by the turn of the bike's wheel. This push lets you lean your bike quickly and turn sharply.

Since a bicycle is in a constant state of imbalance, a cyclist can also start a turn just by taking advantage of the beginning of a fall to one side and transforming this fall into a leisurely turn.



IMAGE COURTESY OF CANNONDALE BICYCLES Libor Karas--Trials Expert "Trials competition is basically bicycle stunt riding over different obstacles, cars, picnic tables, rocks, mud, and water." explained Libor Karas, two-timeWorld Champion Trials rider. The following QuickTime movie demonstrates some of the skills that Libor has developed.



Libor Karas QuickTime Movie (2.4 megs)



The Trials bicycle that Libor rides is smaller than most mountain bikes. This helps him control the bicycle with amazing accuracy. Control is important since Libor does some of his stunts on ledges of tall buildings. Occasionally he even jumps between buildings. When watching him perform, the bicycle appears almost to be an extension of his body.



Braking & Steering Page: 3 of 3

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