Traction Control Dangers and Engine Braking Savior

Are you sure you're seeing traction control and not anti-lock braking? The word "stutter" makes me think anti-lock brakes which shares components, but is a different system.

- Tom

 

Also,

How do you try to stop the car? This sound like a problem for people that are not used to ABS (and is made more appearent on the prius). On the priius the idea is to press as hard as you can on the break and it will try to stop as soon as it can, heck it even has a very advanced logic in there that will sense a fast break pedal depression and try to stop REALLY fast. I'm impressed with how well the car stops (as long as I press the brake pedal hard) even under slippery (parking lot) conditions.

As soon as the Prius detects the wheels as locked it will disconnect the regenerative braking and engage the good old friction brakes. This feels a bit scary as there is a short gap where it feels like you're loosing braking power IT"S IMPORTANT TO NOT RELEASE PEDAL PRESSURE AT THIS POINT. The friciton brakes works with ABS like any other car.

The point is that if your wheels lock you will not use any regenerative braking until you let go of the brake pedal, it will simply use friction. If you release brake pedal pressure when you feel the ABS kicks in ("you loose braking power) THEN YOU LOOSE braking power! This is because you're telling it to brake less! If you keep as much pressure as you can on the pedal it will keep engaging and stops fine on slippery conditions (I can't stop faster)

 

<div class='quotetop'>QUOTE(Silver Phoenix @ Feb 9 2007, 01:55 PM) [snapback]387512[/snapback]</div>

During your rapid stops in snow, it was undoubtably the anti-lock brakes (ABS), not the Traction Control (TC) that engaged. I beleive they both use the same dashboard indicator.

And yes, when the ABS engages, it does take longer to stop then when the ABS does not engage. But, stopping with ABS engaged is a whole lot shorter than stopping with the wheels locked up, which would have been the case without ABS because the ABS does not engage until it detects that the wheels have locked up.

And in any case, whether it was ABS or TC that you encountered, neither one caused you to lose traction, because neither would have engaged until you had already lost traction. Trying to stop faster than conditions allow is what caused the loss of traction.

 

<div class='quotetop'>QUOTE(SomervillePrius @ Feb 9 2007, 02:48 PM) [snapback]387542[/snapback]</div>

While I agree 100% with what you said, it reminded me that this behavior actually cost me a $1000 front axel repair two years ago on my 12-year old Ford Explorer.

My Explorer was getting old and had a cronic problem with the front brakes. The ABS stopped working in the fall (again), and I chose not to fix the problem, because I was just wanting the car to hold out for another year or so before I was ready to replace it, and I wanted to avoid sinking even more money in to it.

So, then comes winter and the snow, and one slippery day I was traveling about 10 MPH and started to slow down and turn into a parking lot. The brakes locked up immediately, the ABS didn't engage, but like I had been trained for 12 years, I pushed and held that brake pedal. I slid a good 50 feet and slammed the front wheel smack into a curb doing at least 5 MPH. Bent the wheel in about 20 degrees compared to the other side.

Of course the moral of this story is not that you shouldn't keep the brake pedal pressed when ABS engages, but rather that you should get the ABS fixed when the error light comes on.

 

<div class='quotetop'>QUOTE(Marlin @ Feb 9 2007, 01:21 PM) [snapback]387562[/snapback]</div>

I've done the same thing three time, at the beginning of each winter, with my old car. For some stupid reason I bought a car with-out ABS last time even though I was trained on and had always driven ABS cars (I will never do this again). When something happens my instinct is to press the pedal hard and keep it there, my dads instinct is to pump or "feel" how much traction he has.

We did a test in his Volvo and neither him nor I can stop a car as fast as ABS IN SLIPPERY or SNOWY conditions (far from), yet for him it's tough to unlearn his 'instinct'. On dry asphalt (with little or no gravel) slamming the brakes and keeping the wheels locked will stop your car a little faster then ABS, but for some reason every time I need to stop a car fast I never have perfect conditions.

I love that the prius senses when you press the pedal hard/fast and will apply maximum brake power right away (faster then your foot is traveling). I have had this kick in a couple of times and while I haven't needed it I"ve been surprised how hard the Prius can stop (in asphalt).

 

The TC or Traction Control only works during acceleration, when you have your foot on the gas pedal. When your foot is on the brake pedal, the ABS is involved.

Overall I prefer a car with the modern safety features like ABS, brake assist, VSC, TC, etc. But I expect these features to be well-engineered, not poorly designed.

A good example is how GM implemented ABS in their pickup trucks in the mid to late 1990's. The system was so aggressive that it could actually make a stop longer than without. I knew a few owners in Utah who actually pulled the ABS fuse just to disable it.

I've posted about how - in my opinion - poorly implemented the Prius traction control system is. Contrary to popular belief, it does NOT pulse the brake of a spinning wheel. Rather, it cuts power until wheel spin stops. It appears for the majority of Prius owners the system works ok, but for some of us, Trac has left us helpless at an icy intersection with one wheel on dry pavement and the other wheel on ice.

One situation where ABS can dramatically increase stopping distance is on a gravel road. If you can lock the brakes, you "dig in" and usually stop quicker. Or if you run studded tires in winter like I do, very slight wheel spin during acceleration and very slight wheel lockup during braking helps the studs "grab"

The whole point to ABS isn't to decrease the stopping distance - since it usually cannot do so - but to keep *control* during a panic stop. Once the front wheels lock, you lose steering ability.

 

The problem isn't the ABS or traction control, it's the crappy tires that come stock on the prius. I've been driving through the worst winter Denver has had in the last 30 years and have been out and about every day. with good snow tires I have not gotten stuck, even in places where other people in SUVs and other 4WD cars have. I haven't lost control, and the traction control hasn't shut the car down.

It you have ZERO traction, the car will kill power to the drive wheels, but don't fool yourself into thinking you could somehow drive out if it if only the car would spin it's tires. Zero traction is still zero traction.

 

<div class='quotetop'>QUOTE(jayman @ Feb 9 2007, 03:57 PM) [snapback]387584[/snapback]</div>

Yup. When my Explorer slammed into the curb (story above), it was not because the car didn't stop, but rather because the car didn't turn. My original goal had not been to stop my Explorer, but rather to slow down and turn into a parking lot entrance. It was even a gently curved entrance, rather than a right angle. The problem was that once the wheels locked up, my Explorer didn't turn and took a nice straight line into the curb.

 

I pointed out near the end of my rundown on B-mode that the "falls
on its face" behavior of letting up the pedal is favored by some
autocrossers, and is definitely useful in the slippery stuff.
.
_H*

 

Hobbit thanks for the writeup. I'll try B around the city and on the gravel road at the hobby farm to see if there is any difference.

 

Oh boy, I hate ABS...

Not that I hate the concept or even application of ABS. I hate the fact that my Corolla's salesman lied to me and told me it had ABS (could've just been wrong, but saying that he lied makes me feel better), and I almost skidded right into an intersection one night when it was rainy and leaves were all over.

I distinctly remembered being told I had ABS, and so I squeezed the life out of those brakes. If I had known, I would've released and pumped.

On a funnier note (because I stopped in time), you should've seen the look on the guy's face in the next lane. He saw my sheepish "oops" grin and just kinda nodded and smiled.

Anyway, now that i know I don't have them, I haven't had a problem. Of course, I will be making sure I get them on the next car (still hoping for the Prius).

 

the ABS on the toyota prius is very sensitive, maybe too sensitive, my 01 prius almost got into a accident one day when there was a patch of ice near a 4 way intersection, the light was red, and i was trying to stop, but ABS kept kicking in making the brake pedal shake ( it was braking every second almost and on the ice it was braking every half second ) , to the point where i stepped really hard on the brakes and not much happened. I then used the handbrakes since i was down to about 15 mph.

Traction control doesnt bother me, its a good thing in some conditions ( in snow and ice, it actually helped me rather than held me back like other drivers ) up here in NJ well, last year snow was kinda on the bad side and the prius proved to be a good car, minus the ABS.

btw the ABS on the prius is very sensitive, i believe this is due to the interconnection of the ABS and the hybrid management system,

 

<div class='quotetop'>QUOTE(narf @ Feb 9 2007, 03:10 PM) [snapback]387594[/snapback]</div>

That's not entirely true. I've seen my wife get through short patches of ice by furiously spinning the tire until friction generates enough heat to melt through to pavement. The downside is that there is a distinct odor of burning rubber--I wonder how many miles of wear the tire suffers in such an event.

I'm not suggesting that the above is a good idea, but it sure is frustrating to sit in my prius with the accelerator floored, unable to move because one tire is sitting on a patch of ice. Couldn't the car at least pretend to do something? My dad always said that having too much power available makes for bad drivers who try to power through every situation--maybe Toyota agrees, and traction control is their way of chiding, "Stop driving like an idiot, it's slippery out there."

 

<div class='quotetop'>QUOTE(hobbit @ Feb 9 2007, 03:22 PM) [snapback]387609[/snapback]</div>

Hobbit

I did try it out in city driving and it feels just like having a stick shift again, actually felt pretty good in city driving. No difference that I could tell on ice, with the studded tires I don't have a problem now.

I can tell though the city fuel economy would really suck if I drove in B all the time, so I won't use it anymore.

<div class='quotetop'>QUOTE(ncc74656m @ Feb 9 2007, 03:53 PM) [snapback]387633[/snapback]</div>

They appear to lie for a living. Good training if they're seeking a future in politics!

<div class='quotetop'>QUOTE(Skeptic357 @ Feb 12 2007, 12:47 AM) [snapback]388737[/snapback]</div>

Or if you have studded tires like I do for winter driving, very *slight* wheelspin really helps as the studs can claw down into the ice and get you moving.

 

<div class='quotetop'>QUOTE(Silver Phoenix @ Feb 13 2007, 01:57 PM) [snapback]389553[/snapback]</div>

I agree. I'm sure most Prius drivers have felt the "lurch" of losing regen braking when a wheel has very briefly slipped. It really gets your attention!

 

SP, sorry if I missed a description of it above, but exactly what are you doing to make this behavior appear?