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Winter Driving Tip - Using ABS
 
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jwernerny
Site Admin
Site Admin
3123 Points

USA US New York
PostYou have posted in this forum: Mon Jan 31, 2011 8:44 pm   Post subject:  Winter Driving Tip - Using ABS Back to top 

Does your car have ABS?

Have you ever used the ABS?

Do you know what to do when the ABS kicks in?

Surprisingly, many drivers don't know if their cars have ABS. Still fewer have ever experienced it, and even fewer know how to react to it.

If you are driving where it snows and you car has ABS, sooner or later you will end up using it, so its a good thing to understand what it can do, and how to deal with it.

First off, ABS will not help you defy the laws of physics. If you are doing 60 mph on glare ice in your car wearing "baldini-speed-special summer tires", you are not going to stop quickly with or without ABS.

ABS only maximizes your control while stopping. It doesn't do miracles. I chose my words carefully. ABS is not designed to stop you as fast as possible, it is designed to give you as much control as possible while slowing the car down by maximizing the braking of the wheels while maintaining their traction. [For some interesting test data from a reader comparing ABS vs. Locked brakes on snow, see this post.]

ABS does this by monitoring the wheels of your car looking for the wheel lockup. When it senses a wheel locking up, it takes over and releases the brakes just long enough for the wheel get traction again (which allows you to steer), and then reapplies the brake until it locks up again. It's like pumping your brakes, except it does it a lot faster than you can. Also, most modern ABS systems actually do it independently to each wheel of your car, so each wheel is getting as much braking as possible. Trying doing that with one brake pedal!

The problem that most drivers have is at the point where the ABS takes over braking. When the ABS takes over, the feel of the brake pedal changes... it changes a lot. If you have never felt it before, it may make you want to take your foot off the brake pedal. That's the last thing you want to do, because that would tell the ABS you are done trying to slow down. Instead, what you really want to do is keep putting your foot down as hard as you can.

Sounds simple. In fact, I had been driving ABS equipped cars for over 20 years when I went to the Bridgestone Winter Driving School and did the stopping exercise. "No problem, hit the ABS, steer around, show them how it's done."

I made my run, then the instructor's voice came over the radio, "Great control, but you could have stopped harder. Not all 4 wheels locked."

If I had done what I was told to do, hit the brakes and keep pushing until the car stopped, the ABS would have individually brought brought each wheel to the point of locking up, thus getting the maximum amount of braking out of each one. Instead, only a couple of the wheels locked while the others where left with some room for more braking. I could have stopped faster!

In fact, what I did is so common that some more advanced ABS systems now detect the speed at which the brake pedal is depressed, and if it is depressed very rapidly (as in a panic stop), they take complete control and force the brakes all the way on.

Moral: When the ABS kicks in, keep pushing!

There is one corollary that falls out of this, and it is also something I learned at the Bridgestone Winter Driving School: If you are under fully engaged ABS braking on a surface where different tires have different traction, the car will pull to the side with the most traction. Why? Because the ABS on that side is braking harder.

[I have debated this one with various other performance driving instructors. Some refuse to believe it, but it is easy enough to try, especially if you live where it snows. Find a safe place where you can put one side of the car on dry pavement and one on snow and drive for a bit without hitting anything if you should loose control. Also make sure there is nothing that will go flying around your vehicle should you stop fast. With your ABS equipped vehicle while driving at about 15miles per hour, your hands firmly on the wheel, and one side of the car on the snow and one on the dry, apply your ABS as hard as you can and see what happens. Feel free to post your results.]

- John

_________________
John Werner - Driving Innovative, Out of the Box Solutions
Editor: The Snow Tire FAQ (http://www.snowtire.info)
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Dave Tire
Frequent Contributor
Frequent Contributor
1364 Points

USA
PostYou have posted in this forum: Fri Feb 04, 2011 8:04 pm   Post subject:   Back to top 

I once had the opportunity to drive a car with ABS and a switch to turn off ABS. It was in a deserted parking where I was able to test brake. It's good to learn the difference but most people won't jam on their brakes to test their ABS for fear of abusing the car.

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Igloo
Real User
Real User
268 Points

Canada CA Alberta
PostYou have posted in this forum: Sun Nov 13, 2011 2:13 am   Post subject:  Re: Winter Driving Tip - Using ABS Back to top 

Re: If you are under fully engaged ABS braking on a surface where different tires have different traction, the car will pull to the side with the most traction.

Few years ago, I had a similar experience as the phenomenon that John mentioned. I was driving about 80Km on a straight highway in winter. I saw a bare strip of dry pavement that was cleared of ice and snow by vehicles tires.

Somehow I felt that I can maintain the stability while braking by having my cars two right wheels on the bare pavement and two left wheels on ice. I reasoned that the two right tires on a high friction surface should able keep the car straight.

While I squeezed down on the brake ( ABS did not engage), the car pulled toward to the right hand side.
The test was terminated.

Conclusion: The braking force on both side of a vehicle must be about the same in order to maintain stability.

In another occasion over twenty years ago, my carís leaky wheel cylinder dripped some brake fluid on the brake shoes.
A car cut into my lane while I was driving at 100Km on dry road. I stomped on my brake. My car pulled to one side and spun around 180 degree

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