Front Brake Question

[BigDon]

The thread on the Bullet section got me wondering.

Does the TLS system on the front brake have significantly less stopping power rolling backwards? Or are my brakes messed up?

The rear brake will hold on a steep hill but the front will allow the bike to roll backwards.

[Cabo Cruz]

Don, I have heard an excellent motorcycle mechanic explain the problem, as follows: The the brakes on a front-leading shoe design are adequate when moving forward and worthless when rolling backward.

I ask our resident mechanical wizards to please provide us with the definitive explanation and answer!

Is there a doctor in the house?

[Roy_d]

Something I pulled out of the dim recesses of my high school memories: Something about the shoe pivoting from one end, and with the bike rolling forward, it will tend to "wedge" into the drum, rather than just drag.  I always thought that on cars, there were two shoes so stopping power in reverse relies mostly on the one shoe placed correctly, or optimally, for that direction of rotation. But it's been awhile . . .  I also await the correct explanation.

[Vince]

      An SLS system works mostly one shoe due to the geometry of the actuator, and rotation direction.  When you go backwards the other shoe is now the leading shoe so braking is the same as going forward. A TLS system is set up to take advantage of the rotation direction. The actuation geometry is wrong when going the other way, so it is not as effective.

[Cabo Cruz]

Vince, I thank you for giving us the definitive answer to BigDon's question.  Even an old guy like me can now understand the limited effectiveness of TLS in relation to rotation direction -- lesson learned, Doc!