Tim McNamara wrote:
Under "maximum braking" the front wheel stops dead, the bicycle
flips, and the rider is ejected. If you are talking about keeping
both wheels on the ground that is far less braking force than
maximum.
That can be circumvented. Build a bike that positions your center of
gravity below the front axle. You could lock the wheel up tight and
still not do an endo.
It actually has nothing to do with the axle, since a locked-up wheel
doesn't rotate, so it effectively stops being a wheel.
The critical thing is the angle of a line drawn from the tire contact
patch to the center of mass of the bike-and-rider.
If this angle is steeper than a critical value, locking up the front
wheel will cause an endo. This is the case for typical upright bikes.
If the angle is shallower than the critical angle, locking up the front
wheel will cause it to skid. This is the case for tandems and many
recumbents.
The value of the critical angle depends on the coefficient of friction
between the tire and the road surface.
For vehicles where the angle is steep, the rear brake is useless at
maximal braking.
For vehicles where the angle is shallow, both brakes are needed to
achieve maximal braking.
Note that the _length_ of the line doesn't matter, only the angle.
See also
http://sheldonbrown.com/brakturn.html
Sheldon "Geometry And Physics" Brown
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| So we'll go no more a roving |
| So late into the night, |
| Though the heart be still as loving, |
| And the moon be still as bright. |
| |
| For the sword outwears its sheath, |
| And the soul wears out the breast, |
| And the heart must pause to breathe, |
| And Love itself have rest. |
| |
| Though the night was made for loving, |
| And the day returns too soon, |
| Yet we'll go no more a roving |
| By the light of the moon. |
| --Lord Byron |
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