mettre sur l'angle

10:38 Mar 18, 2011 

your description is more or less correct, but the force is gyroscopic, not centrifugal. Applying a torque to one axis of a gyroscope generates a torque at right angles to another. Ergo, attempting to turn the bars to the left (ie an anticlockwise torque) generates a torque in the spinning front wheel which is clockwise looking along the axis of the bike. A small deflection in the steering yoke makes each wheel a tangent to the circle defined by the bend, and round you go!

10:24 Mar 18, 2011 

I wouldn't know, I don't ride things that can think for themselves :)

10:20 Mar 18, 2011 

This could be why I found that I had to make a conscious effort not to ride a horse like a motorbike! (A horse has to bend in the direction it is turning.)

10:11 Mar 18, 2011 

You may not be aware of it but, to turn right, you actually start by turning the handlebars slightly left! This causes the bike to turn slightly left while remaining upright. The centrifugal force caused by doing this tips the bike over to the right which then causes it to turn right and the handlebars follow. At the end of the corner, the process is reversed and the bars have to be turned even further right to create excess centrifugal force which tilts the bike back up. This is why you will see many racers crash at the exit of a bend - their front tire is already at the limit of traction and turning the bars can't create any extra centrifugal force. It is almost impossible to counter the gyroscopic forces of two spinning wheels merely by moving your weight about.

09:55 Mar 18, 2011 

OK, while the trees could be reacting to being hugged by Prince Charles, the Pisa edifice is inanimate and definitely does lean! I wish I understood that bit about reverse and orthogonal torque. I always thought that it was shifting my weight that turned the bike and wasn't aware I was doing anything to the handlebars!

21:48 Mar 17, 2011 

The axis of the rider's torso remains in the same plane as the axis of the bike. Except in the exceptional case of racing bikes, a line drawn between the CG of the rider and the CG of the bike is pretty much static. Cornering occurs by the rider applying a reverse torque to the handlebars, generating an orthogonal torque about the front wheel spindle as a result of gyroscopic forces. It seems counter-intuitive, I know, and I was very surprised when I checked it by experiment.
I wouldn't necessarily say that only animate creatures lean. I have seen many trees leaning, not to mention the edifice in Pisa.

21:17 Mar 17, 2011 

As another ex-biker: it is the rider who leans, not the bike, because it is inanimate. By leaning into the corner, the rider banks the bike.

16:26 Mar 17, 2011 

As an ex biker (a long time ago, when 60 HP was thought to be a handful...), I would be tempted to go for a composite of all the answers: a long wheelbase makes it less easy to bank the bike into corners, or just "lean into the corners", or more informally, to crank the bike over