ABS Brakes explained

[Admin]

[old man emu]

Notice that the total braking distance when the ABS is "ON" is longer than the distance when "OFF".

 

That's a danger to the uninformed.

 

OME

 

 

[Admin]

Yes, but more control to be able to turn to the left a little

 

 

[planedriver]

The dog without the ABS, simply dresses to the left (in tailoring terms) and it's Chinese owner calls it Wun-ung-Lo.

 

 

[eightyknots]

Notice that the total braking distance when the ABS is "ON" is longer than the distance when "OFF".That's a danger to the uninformed.

 

OME

This is especially true for unsealed roads. Quite a few people have come unstuck as a result of this.

 

 

[old man emu]

What people don't understand is that ABS is not meant to shorten the stopping distance. The aim of ABS is to permit the tyres to develop steering forces by momentarily removing the friction from braking.

 

TOTAL FRICTION = BRAKING FRICTION + STEERING FRICTION.

 

Actually, a car with ABS will take a longer distance to stop from the same speed on the same road surface as a car without ABS.

 

OME

 

 

[dazza 38]

Yep, Peeps who ride dual purpose motor bikes.Are best to turn OFF ABS if riding in the dirt.ABS doesnt work that well on loose gravel, dirt.It can be like putting on the brakes and nothing happening.Some of the latest and greatest bikes do the job OK. Me , I dont want it on the road or the dirt.

 

Back to aircraft, I dunno about all aircraft, but we used to have ABS on the F111.It used to disengage at about 20 knots from memory.

 

 

[cscotthendry]

ABS or not, you're goin' in the water bucko!

 

 

[old man emu]

You can lead a horse to water, but you can't make it roller skate.

 

 

[cscotthendry]

You can lead a horse to water, but you can't make it roller skate.

Funny looking horses!

 

 

[turboplanner]

I remember my first experience with traction control in the Commodore. Coming home one night, the lights were about to change so hit the gas and, fresh from speedway, threw the car through the corner, only to find the engine slowed down, brakes went on and I came out of the corner about 50% slower.

 

 

[Zibi]

Funny looking horses!

Maybe not roller skate, but some can ice skate:

 

 

[Gibbo]

Yep, Peeps who ride dual purpose motor bikes.Are best to turn OFF ABS if riding in the dirt.ABS doesnt work that well on loose gravel, dirt.It can be like putting on the brakes and nothing happening.Some of the latest and greatest bikes do the job OK. Me , I dont want it on the road or the dirt.Back to aircraft, I dunno about all aircraft, but we used to have ABS on the F111.It used to disengage at about 20 knots from memory.

My Damn Versys is like that. Awsome on the black top but will not work at all on the rock... Damn Damn

 

 

[facthunter]

I thought the theory was that a locked wheel( skidding) had less retarding force than one that is close to locking ( still not skidding)

 

A cornering wheel with sideload at the limit of adhesion will not accept brake or power without slipping ( losing control). The ABS would sense the wheel locking and release the braking force and thereby maintain directional control.

 

Most aircraft of any size have ABS. A max retard stop happens with full brake applied , utilises and relies on the antiskid function.

 

A high speed wheellock will blow the tyre almost instantly. Tyre deflations often occur after the aircraft is stopped due to the heat from the brake assembly heating the wheel to cause the thermal plugs to discharge the tyres for safety reasons. Nev

 

 

[Guest Andys@coffs]

Yeah, Im with Nev. The claim that ABS will always take longer to stop than no ABS is simply wrong. As I understand it normal brakes are their most efficient at stopping us at the point just before traction is broken and skiding commences. As a aresutl the driver has to be super good and break just teh right amount. ABS allows driver to apply every ounce of force he can and the ABS will rapidly and repetitively reduce the pressure if traction is lost thus operating at or very near the most efficient braking force.

 

There are surface types such as dirt/dust etc where ABS has problems determining where traction is lost and in those cases will tend to under brake compared to tradditional brakes, but on normal blacktop roads I believed ABS to be the superior brake solution. When you then add in emergency brake assist (or any of the dozen similar names for the same technology) which detects brake application that is associated with an "Oh F......" moment and it then takes over and says no matter what stop in the shortest possible distance......

 

New car owners that havent ever had that technology, can often be seen open mouthed in surprise when cars are heading in all directions around them in an attempt to avoid hitting them when they have triggered the EBA capability. On my 2 cars it is very effective at stopping and equally effective at significantly lifting the likelihood of someone rearending me. But in genetral Im glad I have it at my disposal after all me hitting someone else = my fault, someone rearending me is a problem for them and their insurance company...assuming I survive :<)

 

Andy

 

 

[ben87r]

I think a "skilled" driver without ABS using the correct breaking will out break an ABS equipped vehicle but, If you break like the Ex and put the brake peddle past the firewall and leave it there until stopped the ABS will win every time

 

 

[ExJourno]

Yeah, Im with Nev. The claim that ABS will always take longer to stop than no ABS is simply wrong. As I understand it normal brakes are their most efficient at stopping us at the point just before traction is broken and skiding commences. As a aresutl the driver has to be super good and break just teh right amount. ABS allows driver to apply every ounce of force he can and the ABS will rapidly and repetitively reduce the pressure if traction is lost thus operating at or very near the most efficient braking force.

Ham-footed drivers are better off relying on ABS... but only until the day the fuse melts when they least want it too.

 

Take it or discard it... but it is a proven fact that burying the brake pedal and activating ABS function in your car versus holding the brake at the edge of skidding sees the car without engaged ABS outbrake the other in a straight line. If you have a third with no ABS it will slide well past both. A bit of time on Google with find you plenty of credible material supporting this.

 

It does not take an overly skilled driver to learn to feel how hard the tyres are working. A few simulated emergency stops will allow anyone to see just how much force they can use before the tyres start to lock up. If your ABS is kicked in you can ease off slightly and ease pressure back on (and repeat if needed) with a faster stop than if you ignored the pulsing pedal. This is a skill easily self taught on a quiet stetch of road.

 

ABS really comes into its own allowing you to steer around something. Though, advanced driving centres commonly teach that you should crash straight and slow rather than potentially lose control steering around an obstacle. The best traction control systems in the world can't compete with a truly ham-fisted wrench on the wheel.

 

Back to the ABS debate, the science is easy. In theory at least, an "ABSing" vehicle applies brakes up to and then past maximum braking force available then locks the tyre and enters a skid then releases the brakes until the skid stops and, assuming the brake pedal is still on the floor, so to speak, starts the process again (allowing the pads to pressure up onto the disk to the point of lock up) numerous times per second. It does not actually hold the car close to the maximum braking possible. This is just not true.

 

THe car not relying on ABS holds itself close to the verge of traction and never releases.

 

The skidding car... well... it just slides down the tarmac with little force being applied between the tyre and the road because the tyre is not "gripping" at the road but rather skating along the top of it.

 

In the earlier days of ABS becoming very common on cars I had a debate (as a newly graded journo back when I was silly enough to be in that profession) with an advanced driving instructor. I argued that ABS meant the fastest possible braking.

 

He proved me wrong by doing three stop tests at willowbank in some grande version of some cheap malaysian/thai/something car.

 

With me in the car to ensure he didn't cheat, he ran down the strip whilst other course participants went to play in the wet braking demo.

 

At 100 we used used a marker line to apply the brakes. Test one was no ABS... except it did kick in slightly near the end but he eased off and reapplied. Next was bury the foot and let the ABS go mental. This resulted in dead stop several metres further. Next was remove the ABS fuse and do a full lock up. As we skidded well past the second marker we'd left, I suggested he had proved his point.

 

THen I repeated the test doing the driving. Same result.

 

This test only works when the same car is used. If you put a Porsche 911 GTS up against a Hyundai Getz and attempt to get the porsche to use ABS versus no ABS but not locking up in the Getz, the Getz will still lose.

 

Incidentally, on this day, I did a 120km/hr to dead stop test in my Holden Barina (Opal Corsa). I was impressed to learn it did a 120 to 0 in 55m dead with a one-wheel lockup during the final two metres... most of the distance used in real life braking was me realising I needed to brake, then moving my foot. It woke me up to some hard facts, some-what.

 

WIth a little thought, you can replicate the test.

 

About a year later, I had an argument over motorcycle techniques with another advanced instructor... he insisted I attend one of his sessions and provided me free passage. A few weeks later at MT Cotton, he proved me wrong too, but that is a story for another day.

 

 

[facthunter]

I don't use an ABS car but the thing about driving well is that is ok if all the wheels brake evenly. You are limited by the first wheel locking up.

 

I did address aircraft. There is absolutely no doubt that ABS is required as you will blow tyres as easy as without it. You couldn't guarantee to do even a moderate stop, in the wet . You have 2x4 +2 tyres or more on the bigger stuff, and some have little or no weight on them, during the roll. The early ones were inertia controlled and the later ones are digital. The on-off is not really noticeable (like it is in some cars where the wheels vibrate back and forth) nev

 

 

[planesmaker]

My Jabiru must have ABS, as there is no way it will ever lock up!

 

 

[turboplanner]

Interesting comments Adam, I've tested a lot of heavy vehicles and in controlled braking in a straight line you can get these results.

 

But if you get a surprise, or if you are unable to maintain a straight line, the results will be different for 98% of the population.

 

Example - when you come round a corner in the mountains on a dark night you have a curve trajectory and the element of surprise.

 

Even the best race drivers in the world screw up their braking from time to time when something unexpected happens.

 

ABS caters for the law of averages - giving you control of the vehicle when you would otherwise lose control.

 

I was doing some work for a manufacturer a few years ago, and came across a great example of just how far this technology has come.

 

The Victorian Traffic Accident Commission were promoting slowing down, by arguing that the average car takes 51 metres to stop from 65 km/hr

 

I found the Iveco Daily 35S14 with ABS and traction control could stop in 42 metres from 100 km/hr at 3.5 tonnes GVM!

 

 

[Deskpilot]

My Jabiru must have ABS, as there is no way it will ever lock up!

The worse brakes on any type of vehicle, especially on the LSA55. Mind you, my Ford Falcon comes a close second.

 

 

[facthunter]

Most U/L brakes are next to useless. On grass you can almost get away without any. The DH-82 tiger moth originally didn't have any and I cannot recall ever being worried about runway length. You need them on tarmac and for steering and taxiing in a crosswind. and Jabiru's at weight need a reasonable amount of speed over the fence so could do with better brakes. The clevelands I had on the Citabria were excellent, so I can recommend them, but you probably wouldn't fit them to anything smaller than a Murphy Rebel.

 

ABS on small planes is not required unless it's something like a Lancair where you can actually have a brake fire if you use the brakes too hard. The ABS won't stop that, but it's that level of performance where ABS helps. Brakes catch on fire because they absorb so much energy with a high speed stop that the heat cannot dissipate from them. Large jets have cooling fans built into the hubs. Nev

 

 

[eightyknots]

The worse brakes on any type of vehicle, especially on the LSA55. Mind you, my Ford Falcon comes a close second.

The Leyland Marina must also come into contention for poor brakes. Many a driver were scared stiff when they saw that their little Marina wasn't going to stop in the distance left, especially when they drove two cars and the other one would have easily stopped in that distance.

 

 

[turboplanner]

That's why the Australian Design Rule system was introduced.

 

It costs us more for our cars, but ADR compliant vehicles have to perform to specific and dynamic targets, so when you get out of one vehicle and into another the brake pedal pressure will be the same and the stopping distance will be the same, the steering effort will be the same, the signal you give to a following driver will be the same (unless augmented by fingers) and so on.

 

I went through the changes and it was a nightmare of changing drawings, bills of material, finding out how to test, redesigning components, finding new suppliers, and we did bitch and squeal about it. I can remember being quite traumatised when Australia lost the ability to produce 16" brakes.

 

But the road toll reduction, in which Australia leads the world can be virtually attributed to Seat Belts, Blood alcohol testing and the ADR's

 

Driving a car today is a dream compared to some of the monsters we had to grapple with in the '70's

 

In fact today you can step out of a Hyundai Getz and get into a B Double and know your judgement of stopping distance will be the same.

 

 

[eightyknots]

But the road toll reduction, in which Australia leads the world can be virtually attributed to Seat Belts, Blood alcohol testing and the ADR's

Driving a car today is a dream compared to some of the monsters we had to grapple with in the '70's

...not to mention the cleaner air we breathe ever since ADR 27A was introduced, along with the upgrades and revisions that followed it.