Re: ABS

["Steve Makohin" <wateredg@xxxxxxxxxxxx>]

Hello Fritz,

From: "Fritz Curtis" <fritzc@xxxxxxxxxxxxx>

> I've been riding 25 years now plus one year on a Harley
> fifty four years ago. (lucky to get rid of that)
> I just bought a 2001 R1100RT-Police bike with ABS.
> For the first time in 25 years I nearly rear-ended a car as my
> attention wandered.  I grabbed my brakes in a death grip and
> of course they did NOT lock up on me and I was able to steer
> around the stopped vehicles in front of me into the space
> between two lanes of traffic. Now here is my question.
> Is it possible to "lay the bike down" ?  Is it possible to "high-side"?
> In my opinion these terms have become obsolete with the advent
> of ABS.  In the twenty five years I've been riding, I figured if I ever
> locked up the brakes, I would surely "lay the bike down".

I am a big fan of motorcycle ABS, so it may come as a surprise to many to
hear me say that yes, you can still "lay the bike down" or "high-side" it,
even with ABS. BMW does a good job in their user manual to warn riders that
ABS is ineffective in circumventing the laws of physics.

Let's first talk about what ABS does. ABS is designed to do one thing, and
that is to prevent wheel lockup under certain conditions (it deliberately
turns off this function at very low speeds to let you come to an actual
stop). In doing so on a motorcycle, ABS helps to prevent skids that could
result in a loss of vehicular control and a subsequent incident.

ABS works really well when the bike is traveling on a straight line, and the
tires have some traction. The more traction, the better. If, for example,
you apply your brakes on glare ice where traction is negligible, the brakes
will lock momentarily, ABS will dutifully release the brakes to allow them
to regain their grip, but there may be insufficient traction between your
tires and the glare ice to establish any sort of meaningful grip. I this
scenario, a skid could result, followed by loss of control and a possible
"lay down".

In another scenario, imagine going around a moderate right turn very
quickly, really leaning the bike into the turn. The tires are near the
limits of traction. The rider, who did not exercise the best judgment, is
riding faster that his "line of sight" (i.e., he cannot stop within the
limits of his line of sight, or in other words, if a risk suddenly comes
into sight, he will not be able to stop before encountering that risk). As
the rider rounds the bend, he notices a slow-moving car entering from a
side-road. Without realizing that the tires have very little reserve
traction left, the rider taps his brakes causing momentary lockup. As ABS
dutifully kicks in to release the locked brakes, the bike has already
progressed its lean beyond the angle of recovery, and has low-sided. There
are many more real-world examples of low-sides, or "laying the bike down",
which may occur, even in much less extreme conditions, and in which ABS will
not be able to prevent a skid.

Now let's talk about "high sides". A high-side is a scenario in which a
motorcycle's rear end looses traction in a turn, and the back end starts to
slide out from under the bike. The rear end the suddenly regains traction,
and violently rights itself, and in doing so, ejects the rider upwards,
possibly completely off the motorcycle into an airborne state. I am going to
steer clear of my own speculation on what ABS *may* do when braking into a
corner in which traction levels change suddenly from low traction (ABS doing
its job an barely keeping the bike from skidding), and then suddenly
encountering high traction mid-way through the turn. I will, however, depict
a scenario in which a rider is accelerating rapidly through a turn, is *NOT*
using his ABS brakes, and for some reason (sand, gravel, accelerating too
hard), the rear end breaks free. Without grip, the rear tire spins up faster
than the bike's speed and the rear end starts to go into a slide. The rider
detects this and lets off the throttle in the hope of recovering from the
low-side. In doing so, the rear-end "hooks up", and violently rights the
bike with such force that the rider is ejected upwards and is airborne.

As you can see, even with an ABS-equipped bike, it is still possible to get
into a lot of trouble. Low-sides and high-sides included. That said, I still
feel strongly that:
 o Motorcycle ABS is a good thing
 o In most cases, it does the right thing
 o On the street, in virtually all cases, riders are better off with ABS
   than without

I urge you to spend some time studying and learning what ABS does, and how
it does it. I'm sure that other members on this list will help out. By being
well-informed, you will have a better idea of how ABS can save your hide,
where it is less capable of doing so, and the scenarios in which ABS is
actually a detriment (if you are unaware of this, it will catch you by
surprise).

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

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