On Fri, 14 Feb 2003, Kim Brennan wrote:

> Hmm, Let me disagree with your analysis, but mostly support your
> conclusion...
>
> Cruise controls work by monitoring the speed of the car...AS MONITORED
> BY THE VEHICLES CONTROLS.
>
> If you are hydroplaning, those controls may not register the actual
> vehicle speed accurately. I've seen a 40 mph difference between actual
> speeds and monitored speed (i.e. speedometer) when hydroplaning (I was
> doing 60 and the speedometer read 20). Rear wheel drive vehicle (VW
> bug) and the speedometer cable connects to the front wheels.

One would think that, to a point, cruise control would help maintain control
as long as it was measuring the speed of the drive wheels (syncro, every
other front-engine car except for the optional speedo on Ford Model A's. :)
If you were going 65 down the freeway and hit a puddle, all the throttle
keeping you at that speed might break the wheels loose.  The measured speed
would increase as the tires slipped, and the cruise would reduce throttle
until measured speed hit 65 again.  At that point your tires might be
slipping still, but it would be close to road speed as long as the puddle
didn't slow you too much.

This isn't to advocate using cruise in poor conditions, especially on
something like the Vanagon that wouldn't easily detect road slip unless it's
extra-smart and watches revs.  The last car I drove with cruise was a 1995
Econoline, and that sucker was squirrely at best.  It had a lethargic
reaction time that made for a rollercoaster-like speed drift combined with
eventual violent downshifts.  (Instead of shifting from 4-3 immediately on a
hill to keep the van at 75, it'd wait till speed slipped to 70 and shift 4-2
-- made quite a racket and threw everybody around but good.)  The trouble in
bad conditions was that if it lost speed on a hill and did that, the scads
of torque and violent shift would break the wheels free, almost ensuring
loss of control.  Whereas if it'd been paying attention it would have been
able to modulate the throttle about as well as person could.

I've yet to own a VW with cruise, factory or otherwise, though I'd happily
accept donations for any OEM components so I can review them properly and
firsthand!

ian Butler / ian@bluemoon.hplx.net
'88 Scirocco 16v, '87 Syncro GL