I finally had to chime in on this one. Please note that this is speaking generally, not specifically. MOST modern cars use the antilock brake sensor(s) to read the speed for the cruise control. This is also how traction control systems work. Normally this sensor is mounted one per wheel, so there are 4 of them to check one another, and the drive wheel, non-drive wheel doesn't matter. Older cars with anti-lock only on the rear wheels will use either a sensor mounted on the diff housing or one sensor each mounted on the rear wheel brake backing plates, or even just on one backing plate, left or right. This happens with FWD cars. With no antilocks, there is a different method. SOME use the sensor that transmits for the speedometer, if the car has an electronic speedo. MOST old cars used the speedo cable to control the cruise. Unless I am mistaken, most old Mopars are in this class. The speedo is driven off the trans output shaft and that is a function of driveshaft spe!
ed, so it doesn't really see the true wheel speed. My 93 Ramcharger used both a sensor for the antilocks mounted on the diff housing and a sensor mounted on the speedo cable, both to check one another. When I disabled the rear-only antilocks (long story) the cruise control began to behave in a funny manner. It kinda keeps the speed, until you go up or down a long hill, then it falls off on both accounts. I don't know if any of this has any bearing at all on hydroplaning, but in the 20+ years of driving that I have done, I have used the cruise in many a rainstorm and never had a problem.
>
> From: "Mark J. Hash" <mjh@xxxxxxxxxx>
> Date: 2003/02/04 Tue AM 10:25:26 EST
> To: L-FORWARDLOOK@xxxxxxxxxxxxx
> Subject: Re: [FWDLK] Safe Driving and cruise
>
> I'm not an engineer, and I certainly don't claim to know everything, but I
> think I may understand how this can happen. Please, someone correct me if
> I'm full of it, but on most cars is not the "set speed" of the cruise
> control set to the pace of the NON-drive axle? Then if the vehicle
> hydroplanes, the non-drive axle is actually slowing, while the drive axle,
> which receives messages from the cruise control, accelerates to compensate,
> causing the wheel spin?
>
> I've never used CC on my 4WD truck, 'cuz I'm offroading when in 4WD, and I
> don't think the manufacturer would recommend using CC in 4WD, so the above
> theory makes sense to me. . . does it to anyone else?
>
> Mark mjh
>
> ----- Original Message -----
> From: "David Homstad" <dhomstad@xxxxxxxxxxx>
> To: <L-FORWARDLOOK@xxxxxxxxxxxxx>
> Sent: Tuesday, February 04, 2003 1:24 AM
> Subject: Re: [FWDLK] Safe Driving and cruise
>
>
> > Now maybe I am not understanding the physics here, but this does not make
> > sense to me. The function of the cruise control is to MAINTAIN a constant
> > speed of the vehicle. I see 4 possible situations here:
> > 1. If traction is lost to the rear wheels due to hydroplaning and the
> > vehicle is under cruise control, the wheels would spin faster, causing the
> > cruise control to reduce the amount of throttle to slow the wheel speed
> down
> > to maintain the “set” speed. Not accelerate the vehicle. Reaction time of
> > the cruise system to close the throttle is important here.
> > 2. If the vehicle is under manual throttle control and the driver
> does not
> > react to a loss of traction and holds the throttle steady, then the rear
> > wheels will spin even faster than the vehicle speed. Reaction time of the
> > driver to close the throttle is important here.
> > 3. If the vehicle is on cruise control and slowing down below the
> “set”
> > speed due to a loss of traction, the cruise would position the throttle to
> > maintain the rear wheels at the “set” speed. This would also cause the
> rear
> > wheel to spin faster (at the set speed) than the vehicle speed (slower
> than
> > the set speed). This may be what the patrol officer meant in the story
> > below.
> > 4. I think the proper reaction of a vehicle under manual control is
> to
> > remove all throttle immediately and coast until steering control is felt
> > again. Do NOT apply the brakes.
> >
> > All of the above applies to a rear drive vehicle, like our ForwardLooks,
> as
> > described in the original story below. Situations 1 to 3 could mean loss
> of
> > control and a spin. The bottom line of the patrol officer’s advice is
> good,
> > even if the “acceleration” of the vehicle idea is wrong. In slippery
> > conditions, do not use cruise.
> >
> > Front wheel drive vehicles may react very differently. When taking your
> foot
> > off the throttle to coast, the engine will cause some engine braking on
> the
> > drive wheels. If the drive wheels are in front, the front drags while the
> > rear coasts. While coasting in slippery conditions, the rear wheels want
> to
> > move faster (less drag) than the front wheels. When the rear wheels get
> > ahead of the front wheels, you are in BIG trouble.
> >
> > Significantly worn or bald tires are a major cause of hydroplaning.
> >
> > Dave Homstad
> > 56 Dodge D500
> > Minnesota, Land of 10,000 Frozen Lakes
> >
> > -----Original Message-----
> > From: Forward Look Mopar Discussion List
> > [mailto:L-FORWARDLOOK@xxxxxxxxxxxxx]On Behalf Of Floyd D. Harper
> > Sent: Monday, February 03, 2003 4:57 PM
> > To: L-FORWARDLOOK@xxxxxxxxxxxxx
> > Subject: [FWDLK] Safe Driving
> >
> > FYI Group:
> > Got the following from a friend and wanted to pass it on for safety's
> sake.
> > I'd never heard this but it makes sense.
> > Floyd D Harper
> > 1960 Dodge Dart Pioneer 2 Door Hardtop
> > = = = =
> > An individual had a wreck a couple of weeks ago and totaled their Lincoln
> > Town Car. She hydroplaned on Hwy. 135 between Gladewater & Kilgore, Texas.
> > She was not hurt, just emotionally rattled!
> > She learned a lesson I'd like to pass on to you. You may know this
> > already--but the highway patrolman told her that you should NEVER drive in
> > the rain with your cruise control on. He said if you did and hydroplaned
> > (which she did) that when your tires were off the road your car would
> > accelerate to a high rate of speed (which it did). You don't have much, if
> > any control when you hydroplane, but you are totally in the hands of God
> > when the car accelerates. She took off like she was in an airplane. She is
> > so thankful she made it through that ordeal. Please pass the word around
> > about not using cruise control when the pavement is wet or icy. The
> highway
> > patrolman said this should be on the sun-visor with the warning about
> > airbags.
> > The only person she found out who knew this (besides the patrolman) was a
> > man who had a similar accident and totaled his car. This has made her
> wonder
> > if this is not why so many of our young people are dying in accidents.
> > Be careful out there!
> >
> > Perform random acts of kindness every day.
> >
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> > 2003 Calendar voting results and ordering information is online! Please
> visit:
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> >
>
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> 2003 Calendar voting results and ordering information is online! Please visit:
> http://www.forwardlook.net/calendar2003 for more information.
>
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