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Hello Robert and list,

From: "Robert Silas" <robert.silas@xxxxxxxxxxxx>

> What is "servo noise" ????  Is that a power brake???  "non-servo
> controlled" brakes"????  it certainly sounds like power brakes.

You are correct. BMW's "EVO" brakes are servo-controlled, which is also
known as "power assisted". Without getting into a lot of technical details,
these brakes sense the brake pressure the operator applies at the hand level
and/or foot pedal, and an electric motor (servo) amplifies that pressure
before sending it to the brake calipers. It is like a car's power brakes.
Basically, the operator needs to apply less pressure to get the same braking
power as compared to unassisted brakes. Additional notes worth mentioning,
some in response to other postings in this thread, are as follows:

o Current motorcycles have awesome brakes that let you do stoppies
  with two fingers' pressure on the front brake, so why does anyone
  need power brakes on a bike? BMW wanted to add the additional
  safety measure that Mercedes calls "brake assist" in their cars. In
  this system, the brake computer senses rapid application of brakes,
  deems it to be an emergency stop, and uses the servo to pump up
  the brake pressure, possibly to fill pressure, faster than a human can.
  BMW's tests show that they save about 1/10 of a second in
  emergency stops, which translates to about 9 feet shorter stopping
  distance from 60 mph to 0.

o The power assist pump makes a whirring or "whizzing" sound, and
  it gets louder as you apply more pressure. That's why these new
  brakes have been nick-named "whizzy brakes" by riders.

o Yes, a car's power-assist brakes also make a sound, but they differ
  from BMW's bike ABS because BMW's pump is driven via an
  electric motor, while a car's power brake pump is driven off the
  crank via a belt. The pump makes a sound, but it's sound is masked
  by the engine noise, and the enclosure around the engine.

o BMW's whizzy brakes provide no power-assist when the key is
  in the "OFF" position. In fact, the brake level requires substantially
  more pressure to activate the brakes than non-assisted brakes. This
  has surprised more than a few BMW riders when they moved their
  bike with the engine off (like from the garage down the driveway),
  only to discover they had "no brakes". (NOTE: BMW bikes with
  whizzy brakes have a warning label top of the fuel tank, and more
  warnings in the user manual regarding this effect, but not all riders
  read all warning notices).

o The whizzy brakes also have "residual braking", a fail-safe
  mechanism that provides full braking capabilities, though with more
  manual effort, in case the power-assist fails.

- -Steve Makohin
 '01 R1100S/ABS
 Oakville, Ontario, Canada