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Re: BMW brakes in the news
- Subject: Re: BMW brakes in the news
- From: "Steve Makohin" <wateredg@xxxxxxxxxxxx>
- Date: Wed, 6 Jul 2005 10:17:30 -0400
John Dancoe <jdan@xxxxxxxx> wrote:
> According to the report, BMW's argument is that "...brake failure...only
> occurred under very specific circumstances..."
> However, the failure which I experienced multiple times was what I would
> describe as ABS "chatter" which resulted in me "holding down the brake
> as hard as I could but the bike just kept going", and the "very specific
> circumstances" were nothing more than bumpy pavement...of which there is
> plenty in Michigan.
> But "insufficient electricity due to overuse of the handbraking
> All that said, I credit BMW for trying to improve motorcycle safety. For
> riders, especially inexperienced ones, it is surely a good thing. It just
> didn't work for me personally; I feel more strongly than ever that
> the ABS is the best thing by far that I've ever done to the bike.
For those who are interested, the Big List is running like a rabid dog with
speculation about (a) the precise nature of the reported problem (as you
know, the 'Net article was vague and did describe the symptoms or
circumstances), and (b) what was meant by BMW's response. Loads of
speculation. No facts.
Interestingly, one list member speculated that a rider *may* have operated
the power-assisted-brake bike with the ignition key on, and the engine off,
for an extended period of time. This could result in a scenario in which the
battery was run down (because the engine is not running and therefore not
charging it), and at some point, the power-assist would stop working on the
brakes, and this may possibly cause the operator to be surprised. Also
written on the list is the observation that if BMW's response was in German,
as one would expect from BMW Corporate, then a few sentences taken out of
the context of a thorough response, and then translated from German to
English, it could result in something that appeared to not "hold water."
Again, I stress this is ALL conjecture, as the article provides little facts
other than someone has a problem and they believe BMW's brakes are at fault,
and BMW doesn't agree.
With respect to John Dancoe's ABS observations, yes, BMW bike ABS responds
suboptimally under some real-world conditions. One such scenario occurs on
level road at moderate speed (say 40 mph), and applying brakes moderately,
say 1/2 (?) but not near threshold of locking. The rider can gauge when the
vehicle will stop under these conditions. However, if a wheel encounters a
significant pavement irregularity such as a sudden dip (sunken man hole
cover, or the location *after* a significant elevated bump), the ABS senses
momentary loss of traction and believes lockup is imminent, and therefore
pulses the brakes momentarily. To the unsuspecting rider, this feels like
the brakes released momentarily (because they did), and therefore increased
stopping distance. This situation is aggravated if a series of such
irregularities are encountered, thereby reinitializing the ABS cycling,
and/or if the rider is going down a steep hill, in which case gravity is
acting as an added accelerator.
BMW's ABS does not fare well under these conditions, and it is best for the
rider of an ABS-equipped bike to be aware of these limitations, and to ride
- -Steve Makohin
Oakville, Ontario, Canada