ABS Brakes.

Tiny
ROCKETMAN007
  • MEMBER
  • 2008 HYUNDAI ELANTRA
  • 90,000 MILES
How have ABS brakes changed since 96'? My 96' Cavalier could nearly stop on a dime on ice. My 2008 Elantra slides like 2 car length before stopping making tapping the brake seem the better option.
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Tuesday, January 5th, 2016 AT 6:07 PM

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Tiny
CARADIODOC
  • EXPERT
Two car lengths? Do you expect the car to stop as though you had hit a solid wall? At what speeds are you going that the car can stop that quickly? ABS systems are supposed to stop working below about three to five miles per hour.

First you need to understand the purpose of anti-lock brakes. It has nothing to do with stopping distances. I've test-driven Caprice Classic county police cars after aligning them and had the chance to experience them with and without anti-lock brakes. A skidding tire has no traction and will slide easier than one that is braking near but not beyond its maximum traction. A real lot of trucks have rear-wheel-anti-lock brakes to prevent the rear of the truck from passing the front when the rear wheels lock up. Cars have a higher percentage of total weight on the rear tires so it makes sense to have anti-lock brakes on all four wheels.

The purpose of all anti-lock brakes is to let you maintain steering control, period. If your front tires are skidding during a panic stop, you can turn the steering wheel all you want to, but you're going to slide straight ahead into that other car. Non-skidding tires allow you to steer around the obstacle.

Getting back to my sad police car story, applying the brakes as hard as possible without locking up any brake will stop those cars much faster than those with anti-lock brakes. With those with ABS, the car will go and go and go, and they'll find you in the next county before the car stops, but you'll always have steering control.

Those cars used the Bendix-9 ABS system. I have a '93 Dodge Dynasty with the Bendix-10 system. The only difference is on the Caprice, when either rear wheel is about to lock up, brake pressure is reduced to both rear wheels together. On my Dynasty, each rear brake is modulated independently. There's more to the story than that because in my Dynasty you'll just about tear the seat belts off their hinges, even when panic-stopping on sand. To understand why, you have to go back to the "skidding tire has no traction". If you have to panic-stop and you hear one tire starting to skid, you'll stop faster if you let up on the brake pedal a little to keep that tire rolling. So you let up on the brakes, but the other three tires weren't at their maximum stopping power yet. Anti-lock brake systems look at all four wheels and keep all four of them spinning even though they are all near their maximum stopping power. All the while this is happening, you have steering control.

Chrysler was the first to have an anti-lock brake system in 1969. Unfortunately it only pulsed the brakes three times per second, which you can do with your foot. Newer systems can pulse the wheels up to 30 times per second, but 15 times is more typical. The valves turning on and off are the buzzing noise you hear when the system activates.

The reason they used to teach you to pump the brake pedal was many driver's can't adjust brake pedal pressure accurately to achieve maximum stopping power while maintaining steering control. Pumping the pedal makes some tires skid, then release, skid, then release. It takes time for a skidding wheel to start rolling again, and by the time it does, you're pressing the pedal again. All ABS systems are much more effective because they never allow a wheel to completely stop turning. Also, they never reduce braking power to any wheel that is not near losing traction. The systems keep each wheel close to its maximum stopping power, but that's just the side benefit. The systems' purpose is to maintain steering control.
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Tuesday, January 5th, 2016 AT 8:50 PM
Tiny
ROCKETMAN007
  • MEMBER
If I'm not going terribly fast why should I worry about steering? I brake because I'm concerned about the car in front of me being too close? Is there something like kitty liter I should apply to my tires so they can stop better?
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Wednesday, January 6th, 2016 AT 5:53 AM
Tiny
CARADIODOC
  • EXPERT
You misunderstood my story. Anti-lock brakes are an option and their purpose is to maintain steering control during hard braking. The systems are designed to cover any type of driving conditions where they will be of benefit. They will not be of benefit at slow speeds. Some systems are real effective at reducing stopping distances, but that is not their purpose. That is just an extra bonus.

Your GM car had a very effective and inexpensive system that works well. But, ... There are always trade-offs between cost, comfort, and effectiveness, and different manufacturers will value different characteristics over others. That's why one car might cost less but the ABS system is real noisy. A different system might provide shorter stopping distances, but cost more. No two car models will act the same way when the system activates.

I'm not sure what you're referring to about cat litter. Are you planning to tail-gate another car, then stop, jump out and sprinkle cat litter or sand on the ground to give you more traction? That doesn't make sense. To a tire, stopping on sand or cat litter is similar to stopping on ice. Sand results in a severe loss of traction compared to on dry pavement.

If you're too close to the car in front of you, simply let off the gas a little and let yours slow down. Even if you apply the brakes, the ABS system doesn't do anything or activate unless you brake so hard that a tire is about to start skidding. It is not uncommon for an ABS system to not activate for weeks or months. The only times it does activate is at speeds where you had better be concerned with steering control. If you start skidding with a car without ABS, it is going to go straight regardless of what you do with the steering wheel, and you won't be able to steer around an obstruction.
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Wednesday, January 6th, 2016 AT 8:40 PM
Tiny
ROCKETMAN007
  • MEMBER
Ok. No I meant cover my tired with kitty liter to improve traction. I saw a car insurance commercial that suggested that in order to get out of parking spot or something. I tried it one time when there was a lot of ice at the end of the driveway and I got my front tires stuck at the end of the driveway so I couldn't get out of the road or leave the driveway.

Anyway another question. Am I at the proper air pressure? At 9:30am having not driven since the day before it was 26 degrees F out and most tires were roughly at 28psi and the sticker in the seams of the door say 32psi is correct. Should 28 be about right considering the temperature lately?

28 psi. 26F. 930am.
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Thursday, January 7th, 2016 AT 6:10 AM
Tiny
CARADIODOC
  • EXPERT
As I recall, tire pressure changes about one pound per ten degrees temperature change. The correct pressure is set when the tires are cold, meaning they're at the current outdoor temperature. When pressures go up due to driving, that is normal but it's not the time to check them.

There is some controversy to this comment, but I always went according to the maximum pressures listed on the sidewalls of the tires when adjusting them before aligning a car. I never had any complaints about harsh ride quality, but that was before we had idiot-politician-mandated tire pressure monitoring systems. When tires were listed as "35 psi max", I made them 35 psi. When they were listed as "44 psi max", I set them to 40 psi. Those pressures gave good tire wear, handling, and ride quality. Those pressure, again, were for cold tires. It is understood the pressures will go higher from driving.
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Thursday, January 7th, 2016 AT 6:23 PM

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