Another Urban Legend - Page 2 - PeachParts Mercedes-Benz Forum

Emmerich · #16 10-05-2007, 12:10 AM

Good point: if the speed sensor is not on the drive wheels, the car can speed up. All cars I had were on the drive wheels. If you went to neutral, the car slowed, engine revved because cruise was trying to compensate.

Hatterasguy · #17 10-05-2007, 12:34 AM

http://youtube.com/watch?v=6sMZ90YGoOE

Unless you have an S class, the new one will just about drive itself..it seems.

waybomb · #18 10-05-2007, 07:05 AM

[QUOTE=Emmerich;1638284]

Second, hydroplaning does not cause wheel speed to increase. When traction is lost, the wheels slip and keep turning while the car slows. The drive wheels are turning at exactly the same RPM as before. Because there is slip, you will normally experience a side slip because both wheels do not lose the same amount of traction and you get a sideways force. The largest force to overcome is the initial slip, once that happens it is easier to maintain slippage.
QUOTE]

You weren't there - the cruise caused the engine to rise in RPMs very quickly. It was only when the engine reved that I knew I was in some sort of trouble. After the engine r's went up, and the rear wheels broke traction, is when I started my slide.

t walgamuth · #19 10-05-2007, 07:17 AM

Quote:

Originally Posted by Emmerich

Good point: if the speed sensor is not on the drive wheels, the car can speed up. All cars I had were on the drive wheels. If you went to neutral, the car slowed, engine revved because cruise was trying to compensate.

If you put it in neutral it is supposed to shut off, i think.

Tom W

thorsen · #20 10-05-2007, 08:29 AM

My 1996 E300 turns off the cruise control if one of the drive wheels looses traction. I hit a small ice patch under a bridge driving back from Christmas last year. The cruise turned itself off.

raymr · #21 10-05-2007, 08:38 AM

Quote:

Originally Posted by waybomb

Hmmmm
I have first hand experience with this in my 1997 C280 Sport.
Headin east on 94, east of Johnson Creek, in a downpour. I had the cruise on. I had it set on 73mph. The tires were in like as new condition.

Came down a gradual hill in the road. Hit the puddle of water at the bottom that was not draining well. The car slowed down quickly, as if I had applied the brakes, the cruise picked up almost just as quickly, and in a fraction of a second, I had started to go sideways. I tapped the stick to get rid of the cruise, and did a nice slow spin, hitting the grassy didvider looking at the opposite direction traffic at a 90 degree angle.

The grassy median in this area, thankfully, was one of the few sections that was relatively flat with the highway, and had no poles or dividers in the middle. The car continued to do a nice slow spin and by the time I was in the middle of the grassy divider, I was pointing in my original direction of travel, and slowing down fast.

I wasn't about to get stuck in the middle, so I gently gassed her and pulled out of the grassy area. My wife about had a heart attack. I had some scratches on the AMGs, and the right inner fender liner that has the air duct in was MIA, but all else was fine. Like it never happened.

I NO LONGER USE CRUISE IN THE RAIN. I don' care what anybody hypothesises.

There is a key point in this story. When you hit a large puddle of standing water, you might not hydroplane, but you will definitely slow down! The CC will immediately compensate, giving enough throttle to possibly break the tires free for a second and you end up fish-tailing, or worse.

TwitchKitty · #22 10-05-2007, 08:17 PM

There are a great many patents to refine cruise control but most companies will not adopt changes until the patents expire and they do not have to pay. A search for "active cruise" or something like that will probably give you plenty reading.

I don't use cruise in bad weather. Some cars are a lot worse than others in this regard.

People who live in areas with hazardous weather generally accept the use of cruise as a bad idea under weather condtions.

Climbing icy hills with the cruise on will eventually land you in a ditch, or worse.