This is coming from someone who was "bitten" by cruise
control, when I had to make an evasive maneuver while
cresting a hill. Even on dry pavement, it made for a wild
ride.
The problem is that Cruise Control doesn't know what you do.
It only knows wheel rotation, and whether it (cruise
control) has been set or released. In addition, there is a
lag between a change in rotaional speed of the wheels and
the response of the system to slow down the engine (the lag
is designed-in, so that the speed changes are gentle under
normal conditions). You experience this somewhat as you are
cresting a hill with cruise-control on. The car will
accelerate a bit before the system responds to the reduced
need for power. Aslo, small changes in speed get gradual
throttle changes, large changes in speed get abrupt throttle
changes, again this is what you'd want under normal
conditions (progressive response).
There are two danger scenarios:
Scenario #1
Cruise control on.
Drive wheels hydroplane.
Throttle position is unchanged, but engine speeds up as a
result of the reduction in resistance to the wheels turning,
wheelspin starts.
Throttle position changes abruptly, as the system tries to
bring the registered speed at the wheels back to the set
speed. Since you're already sliding, the abrupt reduction
in wheel rotation may keep the hydroplane going (or it may
end it).
Things oscillate for a bit until some kind of stable state
between wheel rotation and preset speed has been reached (or
the driver disengages the cruise control), but at this point
you might already be in deep sheep dip.
Scenario #2
Cruise control on, rear wheel drive car.
Front wheels hydroplane. Rear wheels don't.
You now have no steering control, and the car continues on
it's preset speed, when you'd really like to lift the
throttle.
Quickest way to disengage cruise control is to tap the brake
pedal. Tricky to do just right (far enough to disengage the
cruise but not too hard) when you're already a bit
surprised.
Think about it, are inclement conditions (poor visibility,
possibly questionable traction) when you want to turn any
aspect of vehicle control over to a system that knows less
about the changing conditions than you do?
My $0.02
Chris K.
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