I know somebody who got into an accident recently.....hydroplaned in rain in south Texas. Had his cruise control on. The Highway Patrol said that the car will attempt to accelerate if the cruise is on and your tires slip......makes sense to me, but is that true?

 

well that could be true of your speedo registers that the car is slowing down, and the computer tries to compensate, i dunno. thought i'd try.

 

Yes it's true. If your tires start going any slower than what your cruise is set to it'll give gas. If you're hydroplaning or just sliding a little on snow it'll still give gas. That's why you're not supposed to use cruise on anything but dry ground.

 

It makes sense to me, but I'd never thought of it.

 

I'll take exception to that one. The reason you don't want to use cruise in marginal traction conditions is because you cannot feather the throttle correctly to manage wheelspin or maintain power during a slide - not just from straight traction loss.

That description could be correct for some of the old (1960's) Olds Delmonts and "88"s that had the speedometer cable connected to the left front wheel, but since most real cars sense vehicle speed via the driveline VSS (or cable on older models) the slippage of a drive wheel would actually cause the cruise to interpret that as a HIGHER road speed and back off the throttle servo output. Hydroplaning will cause traction loss and overspin of the wheels, not speed loss requiring more throttle. Of course, if you happen to be unfortunate enough to be sitting in a front drive car, that traction loss can also cause loss of steering control. Then again, FWD is not all that great for handling and tracion anyway - it's all sales hype IMHO.

Do a burnout while watching the speedometer. I know MY car isn't doing 110MPH as soon as the light turns green (unless I time the lights just right). If the cruise is set a 65 MPH and the drive wheels start to lose traction, the control is suddenly going to think the car is going over 65 and back off the throttle servo. Since the wheels are spinning, it takes less effort to maintain that rate, so the speed keeps climbing, and throttle output keeps dropping to compensate. The problem occurs when traction is re-established, the speed input suddenly drops to actual road speed, so the cruise applies a LOT of throttle to make up the differential. You lose traction again, and if you're in a FWD car, you probably lose steering, too. (Sorry, sucker. But YOU picked the car...) That's when the tail end can kick outward, and you want to feather the power a bit instead of just dropping it all.

Incidentally, where the F*** does some trooper from TEXAS of all places think he gets any knowledge about marginal traction conditions? BWWAAHAAHAA! Send him on up to No-Traction-Land sometime this coming January - Illinois District 16 troopers could all use a good laugh....

 

What if you were driving through heavy water which caused drag (and you were an idiot to be driving in a condition like that at 75 with the cruise on) and that caused the engine to accelerate, and then hydroplane?

That's how I think it could happy. Just like hitting the gas when you're on ice.

But you're right, what do south texas cops know..........only thing from Texas are steers and queers and that Smokey hat doesn't have horns!

 

True hydroplaning typically occurs with the front wheels, since much of the water is already channeled out of the path of the rears by the fronts. On a RWD car there would be a loss of steering control, but road speed would be accurate.

As I mentioned before, on a FWD car there would be a loss of both steering and traction, so the front wheels would tend to overspin on a FWD until the cruise reacted and removed throttle. Yet another strike against the "better traction" FWD scheme.

 

I agree with you vader. This is what I mean. Maybe I should've been more specific.

If you lose a little traction your cruise does not know. Your cruise will maintain the car at set speed. Now, if your tires are spinning you have no more drive (forward load). Consequently you'll start slowing down in real life. Your cruise will maintain set speed at the rear wheels. So say you drop to 50 due to spin, your tires will maintain 55. You drop some more to 45 and your rear tires will add power to maintain 55. This can become a problem. It's not so much with hydroplaning as with snow/ice.

 

Once teh drive wheels break loose, the force required to matian speed will reduce, so the cruise will (slowly) reduce throttle angle. It shouldn't add any throttle until the load increases, and since road speed is sensed by the cruise via the drive wheels, it won't know any better and will maintain drive wheel speed.

I understand your point, but if anyone driving a car has reactions that are that slow, they shouldn't be driving a car - especially in marginal traction conditions.