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#192150 - 12/30/09 08:40 AM Re: anti lock brakes question [Re: dougwalkabout]
MostlyHarmless Offline
Old Hand

Registered: 06/03/09
Posts: 982
Loc: Norway
Doug has it right. ABS works, and does a better job than even most experienced drivers. Perhaps you can construct an idealized a setup where a racing driver can brake+steer/control the car slightly more efficient without ABS, but that will be a rather special case.


If you feel the ABS kick the pedal - the immediate response is to press it all the way down and let the ABS do what it does best. The car will go straight and you can think out what to do next while you get a gentle foot massage. Exercise in an empty parking lot so you know what it feels like.

After the immediate situation is resolved, take the ABS response as a strong indicator THAT YOU ARE GOING TOO FAST! Your driving behavior is exceeding the traction provided today. Slow down. Drive gently. Imagine you've got a rotten grape between you and the controls - don't crush that grape!


I still practice the art of releasing the brake before steering - I learned to drive before ABS and that response is hard wired into me. I don't know how good that "hardwiring" will be in a true emergency braking situation, though... never been there yet, but ABS will be a huge asset in that situation.

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#192151 - 12/30/09 01:04 PM Re: anti lock brakes question [Re: MostlyHarmless]
chaosmagnet Offline
Sheriff
Carpal Tunnel

Registered: 12/03/09
Posts: 3821
Loc: USA
When buying a car, I always make sure that it has disc brakes at all four corners, and four-channel independent ABS. That way, each wheel gets the best braking available in situations with reduced traction.

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#192155 - 12/30/09 01:48 PM Re: anti lock brakes question [Re: chaosmagnet]
KenK Offline
"Be Prepared"
Pooh-Bah

Registered: 06/26/04
Posts: 2208
Loc: NE Wisconsin
Raven,

I tried to send you a private message, but your in box is full. If you're still feeling uncomfortable I know people who may know people who can help you (I'll save the details for a PM).

Ken


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#192164 - 12/30/09 04:04 PM Re: anti lock brakes question [Re: dougwalkabout]
Eugene Offline
Carpal Tunnel

Registered: 12/26/02
Posts: 2995
Originally Posted By: dougwalkabout
\: even the crudest ABS pumps 5-10 times faster than I could manually. On an icy road, downshift gently and let the engine slow you down, then if necessary punch those ABS brakes and hold 'em. Your job is to steer ... toward the curb where the road is less polished; or straight into the snow-filled ditch; just don't hit another car or a whole 'nother bunch of ugly kicks in.

Yup, basic ABS kicks the pedal. But the bottom line is: ABS works.


Actually it doesn't pump, it attempts to threshold brake but modulating the valves and therefore the pressure on the brake pads.

I find most ABS systems to be too sensitive, they will release the pressure too quickly or as someone said any time one wheel slips slightly. Of course if they put more delay into their engagement then their reaction time is less than that of a human so its a difficult balance bewteen the two.

With a lot of modern city streets having large dividers or curbs there isn't any place to steer either so some situations your better off letting the wheels lock and piling up anything they can dig loose in front of them. Thats the fundamantal problem with systems like ABS, traction control, etc they are all reactive to the limited number of inputs they have, can;t see the road ahead or determine if they shouldn't engage in the current situation. IMHO stricter driving tests would be much better.

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#192176 - 12/30/09 06:14 PM Re: anti lock brakes question [Re: thseng]
James_Van_Artsdalen Offline
Addict

Registered: 09/13/07
Posts: 449
Loc: Texas
Originally Posted By: thseng

Thus when one wheel hits a patch of ice just as you roll up to a stop sign, the brakes on the other three wheels release and you skitter into the intersection, because God forbid that one wheel should skid a little.

That's a cheap/poor ABS system. A decent system is a "4-channel" where each tire is monitored and managed independently.

A friend of mine races cars in varying degrees of modification and I asked about ABS in racing once. He says there is no way at all for any human to modulate brake pressure as well as a decent ABS system, but that since he's "driving way ahead of where the car is" he can win by not using ABS - he can anticipate what the situation will be and not just what it is. So he races without ABS, but off the track he always has it on.

Short stopping distances is only one goal for ABS. Control under max braking is just as important: if the wheels lock up the car will spin if there's even the slightest angular momentum at the start.

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#192179 - 12/30/09 06:39 PM Re: anti lock brakes question [Re: James_Van_Artsdalen]
thseng Offline
Old Hand

Registered: 03/24/06
Posts: 900
Loc: NW NJ
Originally Posted By: James_Van_Artsdalen

That's a cheap/poor ABS system. A decent system is a "4-channel" where each tire is monitored and managed independently.

In that case I admit that I've only ever driven vehicles with cheap/poor ABS systems that modulate the overall brake pressure, rather than each wheel individually.

In that case I can see that a high-end four channel-system could result in a shorter stopping distance under most conditions. The wheels with the most traction get the most braking, while if one wheel hits a slicker spot only the braking on that wheel is relaxed.

_________________________
- Tom S.

"Never trust and engineer who doesn't carry a pocketknife."

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#192181 - 12/30/09 06:49 PM Re: anti lock brakes question [Re: James_Van_Artsdalen]
7point82 Offline
Addict

Registered: 11/24/05
Posts: 478
Loc: Orange Beach, AL
ABS kickback through the brake pedal varies quite a bit from one vehicle to another. Newer vehicles are getting progressively better about minimizing it.

All ABS systems are not created equal. I have a '02 Honda Civic that used to be my daily driver. Overall it was a great little car but the ABS system on it was pathetic. It's the one ABS equipped car I've owned that I honestly think I could have done better without ABS.
_________________________
"There is not a man of us who does not at times need a helping hand to be stretched out to him, and then shame upon him who will not stretch out the helping hand to his brother." -Theodore Roosevelt

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#192224 - 12/31/09 12:51 AM Re: anti lock brakes question [Re: ironraven]
Hanscom Offline
Journeyman

Registered: 11/23/05
Posts: 86
The big point about ABS is that you can still steer the car with the brakes on full and ABS massaging your foot.

If you lock up the wheels with conventional brakes you are no longer a driver; you have become a passenger. The car slides wherever it wants to.

Yes, if you are very good and very, very practiced, you may be able to keep the wheels on the edge of lockup, but it is unlikely in an emergency situation.

For a test, go out on a straight, smooth, DRY road, preferably highway. 40 MPH for the first test. Check that there is no one behind you for a half mile. Put your foot in it--HARD--and leave it there. Second time do the same and steer a little.

This is good experience in general. You do not want to be in a life threatening situation and be checking your car's capability for the first time.

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#192268 - 12/31/09 12:10 PM Re: anti lock brakes question [Re: Hanscom]
Eugene Offline
Carpal Tunnel

Registered: 12/26/02
Posts: 2995
I did that test in an empty parking lot the first big snow after I got the vehicle. Go out and hit the brakes on the snow/ice and see how it reacts. This was a 3 channel and I could stop better with the abs fuse out every time.

Wife's car doesn't have ABS, we had went to dinner with her parents one time and were on our way back when we came aross a highway overpass and there was an accident in the other lane so right in the middle of the bridge, even though the accident was on the other side of a big cement divider the person in front of us decided she needed to come to a complete stop. I slammed on the brakes and started skidding then said out loud "oh yea, no ABS" released the pressure enough to get traction again and went around her. Of course keeping a safe following disatnce helped there too. I've seen those studies online that say ABS hasn't decreased accident rates since people get over confident because of it and drive a little more riskier.

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#192319 - 01/01/10 02:38 AM Re: anti lock brakes question [Re: Eugene]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
Sad but too often true that, Eugene. All the statistics I have read said that on their own the various safety systems should prevent X number of accidents and Y number of fatalities. But they only see X/2 reduction in accidents and Y/2 reduction in deaths because people who think the cars will better avoid accidents and save their lives tend to drive carelessly.

Its like the old joke that says if you want to have people drive carefully you would take out the seat belts and rig a foot long iron spike pointed at the heart of the driver in the middle of the steering wheel. Nobody would speed or drive unsafely. In fact few people would drive and those that did wouldn't go over five miles an hour.

People who think, even if it subconscious, that the ABS system will allow them to get away with tailgating and air bags will save their lives tend to take more risks. It doesn't entirely cancel out the benefits of ABS and airbags and the rest of the safety systems but we never see the full benefit either.

My biggest problem with ABS systems is that for them to work their best you need to stomp on the brakes and maintain pressure. Which goes against twenty-five years of training and experience. I reflexively back off the pressure and pump the brakes and it takes a conscious effort to, what used to be called, drive like an idiot.

I'm pretty proud that last time I had to stop fast, after a car stupidly pulled out in front of me, I hit them hard and maintained pressure. I'm also glad that he ABS system worked. I'm still not sure if I could have stopped in time if I had pumped the brakes. But I'm sure that driving like an idiot, braking hard and holding it, if the ABS hadn't worked there would have been a crash. The end was happy because the primitive ABS system on my truck, rear wheels only and one channel, worked. But it still feels weird to be depending on a mechanical system to do what I'm used too be doing on my own.

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