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Discussion Starter #1
So the majority of us know (or think that we know) about the advantages of ABS, right, and how the bleeding of ABS brake lines can be a major pain in the butt, but how many truely know how ABS works physically and electrically?
My question comes from reading a thread on Strom 650 2017 ABS brakes, where the poster (2017Vrider181) writes: 'Hi stromers, d'like to know if one of you have found a way to disconnect the rear abs brakes, keeping the front abs working. I really don't like the way the rear brakes work in the trails. I'd really like to stop the rear wheel when i'd like to. I know I can remove a fuse in the ABS module and then both front and rear brakes abs disengage. But is there a way to only disconnect the rear abs brakes."
There are a few threads on this site (eg http://www.stromtrooper.com/v-strom-modifications-performance/15975-how-abs-off-switch.html) and the VSRI site (eg Proper ABS on/off switch) of mods / ideas to switch off the ABS as a complete unit.
So after looking at a possible solution for switching off ABS to selected wheels, I started by looking at an earlier model DL650A wiring diagram. I saw that the sensors have connectors that could be a possible disconnecting point. Then I thought, since the ABS only activates above 5 mph, the ABS unit may see the disconnection of the connector as a wheel locked and try to pulse the brake caliper, which is not what is being sought.
Reading https://www.vicroads.vic.gov.au/safety-and-road-rules/motorcyclist-safety/how-abs-works-on-motorcycles gives some back ground to ABS purpose, but does not explain everything. Hopefully with your help readers will give a better understanding, that the members can use for future reference?
 

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I've read on here where if the differential is too large between front and rear wheels, something happens with ABS. Don't remember if it's activate or deactivate. I am going to assume that if there is NO differential, ABS is none the wiser and continues to function normally. I was thinking one method to fool the system would be to install a switch that intercepts and cuts the sensor signal from the rear wheel and replace it with the sensor signal from the front wheel so both receivers would be getting the same signal. Then realized that works until you lock the front brake. The system would then release both brakes. I do think, though, that sensor signal manipulation might allow more alternatives than switching the fuse to disable the entire system.

Does anyone know what differential threshold triggers the ABS to take action?
 

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On fooling the ABS, or defeating rear brake easing

It is a bad idea to feed the ABS computer's two wheel speed inputs from the same sensor. Doing so will make the ABS non-functional because it relies upon sensing the beginning of lock-up on one wheel, relative to the other, so that it can determine which brake should get reduced pressure. Without that differential appearing when a wheel begins to slow (while the other continues at "full" rotation rate), the ABS will never activate and will be useless.

Disabling the rear brake release actuator might be useful, or not. Most likely not because when that actuator would do something, the rear wheel is slipping and can no longer provide a good reference speed for sensing that the front wheel is slipping. The ABS could become merely useless, or maybe worse. (I would have to know its fault detection algorithm better to decide.)

When the wheel speed differential becomes too great while no brakes are applied, the ABS disables itself and turns on the yellow panel indicator to warn the rider that the ABS is not going to function for the rest of that engine-on cycle.
 

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Discussion Starter #4
The worrying factor about ABS is when is it going to let one down, when a person totally comes to rely on this feature.
I have seen some drivers barrel down to an intersection only to hit the brakes at the last minute. I've noticed witnessed these drivers, a few times, not only here locally, but when I was driving abroad as well.
There have been a few threads posted of ABS pump failure on the V-Strom and other brands. Some say that it is due to the ABS not being activated / tested on a regular bases.
I believe that ABS has it uses, when it doesn't fail, they work well on my cagers. After riding bikes for so many years without ABS, I think that I'll remain with my non-ABS rides for a while longer...
 

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On my G650GS BMW there is a switch to turn off the ABS for dirt riding. The rear brake is like my 800ST BMW on the street in ABS operation...it feels like a hammering when engaged. Not a good, positive brake feeling. Not sure you'd want the front wheel ABSing in the dirt with the rear locking up.
Different systems on different models, the ABS always felt good on my '01 R1100RT-P
 

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The worrying factor about ABS is when is it going to let one down, when a person totally comes to rely on this feature.
I have seen some drivers barrel down to an intersection only to hit the brakes at the last minute. I've noticed witnessed these drivers, a few times, not only here locally, but when I was driving abroad as well.
There have been a few threads posted of ABS pump failure on the V-Strom and other brands. Some say that it is due to the ABS not being activated / tested on a regular bases.
I believe that ABS has it uses, when it doesn't fail, they work well on my cagers. After riding bikes for so many years without ABS, I think that I'll remain with my non-ABS rides for a while longer...

Assuming that there isn't an ABS warning light (on the dash) how would one know if it's functional?

Other than practicing panic stops and deliberately activating the ABS it should never come on in normal riding.

It's been proven over and over that ABS stops a bike faster than even a highly skilled rider can without ABS. Mere mortals definitely benefit from having ABS.
 

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LOL, we had a rider in our club on his '05 Yamaha R1 that said he could out-brake an ABS-equipped rider every time.
I didnt know that was a contest. Funny, he had more than his share of wrecks than most.

When I attended Subaru ABS training and a BMW motorcycle ABS demo-rides, the emphasis was not on how it braked faster with ABS--the main deal is that a locked wheel can't be steered. By allowing the wheel to be steered with controlled, pulsed braking, steering control was retained.

At Subaru, we went out on a parking lot, rolled out a 100'+ length of vinyl mat and hosed it down, then sprayed dishwashing liquid over the water. As per instruction, I picked up speed in a Legacy sedan to 50 mph, hit the mat an slammed on the brakes. The car went sideways, slid back and forth, finally got it to a stop well beyond the mat. The next Subaru I tried had the then-new Bosch 5.3 ABS system. Same deal, except the car stopped on the mat straight and sure with no drama except for the normal pedal pulsation that occurs during ABS operation.

The main issue people had with ABS was 1) the pedal pulsations freaked them out, to the point where: 2) they let off the pedal, which stopped the ABS operation....and they lost control and crashed.

Yes, ABS cars do stop in a shorter distance, hence possibly quicker, but the main purpose is to allow the operator to maintain steering control.

I'm waiting for the day where, on motorcycles, the ABS unit will activate ABS regardless of brake application in the event of following too closely based on a radar sensor signals, or the operator isnt on the brakes in time to prevent an accident.
My '19 Mazda CX-5, and many more cars these days are so equipped---and twice now I've had the "pleasure" of experiencing this system do its thing.
 

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(I'm not contradicting previous posts on ABS virtues.)

A very important benefit of having a (well designed and working) ABS is that, when brake pressure is high enough to activate the anti-lock easing, it effectively gives the rider very close to the maximum available stopping traction, on each contact patch independently, for the roadway conditions at each contact patch. I am pretty sure that the demos we can see, where some expert rider out-stops an ABS equipped bike, are done on a track with very consistent pavement texture and wetness, and done with the rider having had enough practice under those conditions to know how hard each brake can be applied. This is nothing like what we experience out in the wider world, where some portions of pavement may be slightly oily, some dry faster than others, not-quite-visible debris can be present, often in short stretches, and the pavement changes with rework, application batch, etc.

I practice maximal braking stops without the ABS, to be sure that I remain skilled enough to handle an ABS failure. But when somebody violates my right-of-way and it is time to slow quickly, and my attention is on several things beyond the degree of slide at each contact patch or pavement conditions along my chosen evasion path, I am glad to have a fast-reacting ABS computer giving me nearly all the stopping force that is actually available, even as conditions vary along my slowing path. Add to these complications the fact that I may need to execute a slight turn at the same time, and the benefit increases further. I find it very difficult to believe that such scenarios could be improved upon by a more skilled rider. (And, even if such a super-rider exists, he cannot take my place when my life or limb is in jeopardy.)
 

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When I was a younger man I did a advanced driver course, I was the youngest in the group and was fist to be picked on.

I was told drive down the hill, lock the brakes up then steer between the red cones and stop in the box.

It was fully expected I would just skid straight ahead and skittle all the cones.

I did not, after locking the brakes as required and washing off some speed I manoeuvred around the cones and came to a stop in the box.

The instructor asked if it was first time at a driving course ? "yes", who taught to drive ? "my dad" where did I learn to drive ? "in a state forest" BINGO he said....

Learning to drive in the dirt as a young fella had given me skills I never knew I had, a inbuilt ABS.

In the dirt you quickly learn that panic braking will cause more problems than it will solve.

I give a lot of my time to young kids that visit Rolex teaching them to ride and drive, a skill I believe has kept my alive all these years and will help them survive into the future too.
 

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The worrying factor about ABS is when is it going to let one down, when a person totally comes to rely on this feature.
I have seen some drivers barrel down to an intersection only to hit the brakes at the last minute. I've noticed witnessed these drivers, a few times, not only here locally, but when I was driving abroad as well.
There have been a few threads posted of ABS pump failure on the V-Strom and other brands. Some say that it is due to the ABS not being activated / tested on a regular bases.
I believe that ABS has it uses, when it doesn't fail, they work well on my cagers. After riding bikes for so many years without ABS, I think that I'll remain with my non-ABS rides for a while longer...
In general, the ABS system will extend your breaking distance. ABS is intended to prevent loss of control by trying to keep the tires rolling instead of sliding.

I thought it was interesting that on Suzuki's website product page for the 2014 DL1000A, the text warning about the increase in stopping distance was 2 to 3 times longer than the text touting its virtues. Even the current lean sensitive ABS still bears a "black box" warning paragraph front and center that is about 1/3 the size of their entire sales pitch...
 

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The way I understand it is that when ABS control system senses that a wheel has stopped turning, the ABS pump then has to relieve hydraulic pressure without being able to reduce input from the driver's foot. This is a difficult, high pressure, task since it must isolate then pump backwards against the driver's foot to get pressure off the brake pads. It does this in rapid succession so you get periods of full driver pressure (lock up) and reduced pressure (ABS kicking back). It is this period of reduced braking force to allow the wheel to roll again that extends your braking distance.

I have yet to own or read about a vehicle (non-regenerative braking) with a level of hydraulic sophistication to linearly modify the hydraulic pressure within the brake system to achieve the maximum allowed braking force for the given (and continuously changing) conditions between the tire and the road surface. Incidentally, available friction between the tire and the road cannot be measured directly and would have to be measured by the ABS control based on the wheel locking up. To find the "point" between lockup and roll, the system would have to trial and error probe by using different braking forces until it can see which locks up and which doesn't. A top down approach would include extra lockup sliding in that critical initiation phase until it softens up enough to start rolling again. A bottom up approach would result in less slide, but softer braking (and longer distance) leading up to and including some lock up slide, then restoring back down to roll. All of this would take time especially since the point between lockup and roll is constantly changing during the braking maneuver.

Also, for the ABS to exert that level of control over the hydraulic pressure within the vehicle's brake system, it would have to remove / override any input from the driver or be a braking by wire system to begin with. It would also be difficult to mechanically modulate to an exact hydraulic pressure and certainly would require more than just the gross stroke pulsating pump we are all familiar with.
 

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If I read this thread correctly, either I don't understand ABS thoroughly...or there is a large amount of misinformation regarding the operation of ABS.

ABS operates by measuring the wheel speed (revs/min) at each point: front and rear for a motorcycle and all four wheels for a modern car. The ABS operates on each wheel of the Strom with the radially slotted ring on the F/R hub, and the sensor, which reads a magnetically-generated electric pulse as each "spoke" and "space" moves past the sensor and sending it to the CPU. The CPU monitors the speed of each wheel and when it senses a discrepancy between the two--presumably with some margin of tolerance--it triggers a bypass circuit in the valve body that very rapidly opens and closes a valve in the hydraulic circuit to the wheel experiencing the slip (which would relate to the wheel being over-braked) to relieve the line pressure to the brake circuit of the target wheel. It is this rapid opening and closing of the valve that the operator feels as pulsing.

Bottom line, this means there is no way that you can JUST disable one wheel ABS function, since it necessitates a continuous signal from both wheels to function. With respect to the fallacy that ABS results in longer stopping distances, this applies ONLY to braking in off-road situations and in rarer cases, in deep, wet snow (applies primarily to cars). It is true that there has been some "research" by enthusiast magz where world-class racers were able to stop as short or slightly shorter without ABS than with. However, it is a result of that rider's greater ability to control the vehicle' stability at threshold braking forces and not because ABS is less effective at stopping. For us ordinary folk--read that as NOT world-class racers!!!--ABS will always help us stop on pavement, dry or wet, more safely and in shorter distance than non-ABS.
 

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how ABS works

The way I understand it is that when ABS control system senses that a wheel has stopped turning, the ABS pump then has to relieve hydraulic pressure without being able to reduce input from the driver's foot. This is a difficult, high pressure, task since it must isolate then pump backwards against the driver's foot to get pressure off the brake pads. It does this in rapid succession so you get periods of full driver pressure (lock up) and reduced pressure (ABS kicking back). It is this period of reduced braking force to allow the wheel to roll again that extends your braking distance.

I have yet to own or read about a vehicle (non-regenerative braking) with a level of hydraulic sophistication to linearly modify the hydraulic pressure within the brake system to achieve the maximum allowed braking force for the given (and continuously changing) conditions between the tire and the road surface. Incidentally, available friction between the tire and the road cannot be measured directly and would have to be measured by the ABS control based on the wheel locking up. To find the "point" between lockup and roll, the system would have to trial and error probe by using different braking forces until it can see which locks up and which doesn't. A top down approach would include extra lockup sliding in that critical initiation phase until it softens up enough to start rolling again. A bottom up approach would result in less slide, but softer braking (and longer distance) leading up to and including some lock up slide, then restoring back down to roll. All of this would take time especially since the point between lockup and roll is constantly changing during the braking maneuver.

Also, for the ABS to exert that level of control over the hydraulic pressure within the vehicle's brake system, it would have to remove / override any input from the driver or be a braking by wire system to begin with. It would also be difficult to mechanically modulate to an exact hydraulic pressure and certainly would require more than just the gross stroke pulsating pump we are all familiar with.
I think you misapprehend how an ABS works in practice. And I venture that you have not seen or done the experiments necessary to support the "ABS extends stopping distance" assertion. I do not dispute the qualitative details of your stated understanding, but I do dispute the implied quantitative conclusion you state. Here is why:

First, to know why ABS is useful and can provide stopping force very close to the maximum available from each contact patch, it is vital to understand the traction versus slip function for rolling rubber pressed against pavement. I relate the following from a plot of this function I find in a compendium of papers commissioned by the U.S. Department of Transportation on tire characteristics and behavior. (I have provided a link to it in one or two previous posts.) At zero slip, there is zero traction. As slip increases, traction rises rapidly, linearly at first then less rapidly as the curve bends around to a peak. (I refer to this as the "traction peak" later.) As slip increase further, there is a much more gradual, more-or-less linear reduction of traction to a little over 50% of peak traction. Considering slip beyond that is pointless, as nobody operates there on a motorcycle except to put on a show.

The functional purpose of the ABS is arrange to keep the slip near where the traction peak occurs. It does this by exploiting the negative slope on the far side of the traction versus slip function. As braking pressure increases to the level that force on the contact patch drives slip over the top of that curve, the reduction of traction results in a slightly regenerative phenomenon where the slip begins to increase rapidly. (This is rapidly relative to human perception time.) That is when the ABS computer detects the increasing slip and eases brake pressure. It does not release all pressure, nor does it ease enough to let the wheel get back to low slip; it eases enough to let the wheel speed get back to where slip is near the traction peak. This is a cyclic process, with slip moving back and forth over the traction peak but staying near its maximum.

It is a common misconception that ABS lets off the brake, and that a good rider can do better by applying just the right brake pressure. The former is wrong and, in my opinion, the latter is folly. The problem is that a rider cannot know that a contact patch has gone over the top of the traction peak until much more slipping is happening than the ABS can detect, and so traction is given up during the detection lag and brake easing.

It is simple to tell how much the ABS eases braking pressure. Do a maximum braking stop, so that the ABS pulses for most of it, and concentrate on how much the force of your hands on the grips changes as the pulsing happens. It is practically undetectable. The force you feel as you approach the deceleration where the ABS activates is indistinguishable from the force you feel while it is fully acting to modulate brake pressure. (This is not a theoretic prediction alone. I have done this experiment to see for myself.) This shows that ABS operation is barely affecting deceleration.

FWIW, I have become familiar with ABS operation as a result of having it explained to me by a Boeing engineer. ABS has been used on commercial airplanes for many decades.
 

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Please note that it is not my conclusion that ABS extends braking distance it is the published conclusion of the manufacturers of the systems.

Your explanation is very similar to mine. I never said it releases the brake it just reduces pressure inside the brake lines. The studder felt at the controls is pronounced.

Two points I was trying to make... A graph on paper measured in a lab does not reflect in use operation and real world road / traction conditions. The graph will change depending on the road surface, condition, debris, weather, temp, etc. The ABS cannot measure the traction directly and it cannot just play against a known experimental graph, it can only measure a difference in spin rates between the tires (partial or full slip). When a wheel slips ABS needs to back off the hydraulic pressure. It cannot bypass (bypass to where?) it must act inline between the master and slave, there are no recirculation loops. It would have to hold back or block the master cylinder and relieve some downstream pressure on the slave cylinder side in order to achieve its goal. It could accomplish that by isolating the master and oscillating the volume of the down stream brake lines with the pump piston. Is that volume adjustable on the fly? Or is it preset by pump design at the factory? If the latter it has even less chance of perfectly modulating pressure to "ride the hump" of the theoretical traction graph to maximize traction and braking force.

How tightly it can "ride the hump" would determine how close to maximum traction (and braking force) it can stay. Can the systems of today react fast enough to modulate each ABS pulse based on a direct wheel spin measurement? Or are they still following a preset pulsing curve? The former could ride the hump very tightly, the latter no so much. The former would need to be lightning fast both in processing, actuation, and feedback, perhaps impossibly fast. Chances are the aircraft you mentioned have the most sophisticated ABS at a cost greater than all of your and my vehicles combined.

It is my assertion that the manufacturers know the size of the gap between the theoretical operation you describe and the real world performance achieved by their budget ABS implementation and therefore publish the statement that their ABS can increase stopping distance. I have not yet seen the manufacturers claim that their ABS can decrease stopping distance. They do, however, routinely claim that their ABS can help maintain control during braking by reducing skidding.

In my personal panic stop experience I have ALWAYS experienced a decrease in deceleration while the ABS is active. For example during hard braking I feel (not measure) deceleration, at the point that ABS goes active, I feel less deceleration, every time. Perhaps my vehicles just aren't sophisticated enough...
 

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Please note that it is not my conclusion that ABS extends braking distance it is the published conclusion of the manufacturers of the systems.
(I say this to those who may share your interpretation.) We need to distinguish lawyer-advised ass-covering statements from meaningful facts that should influence our actions. Take note of the fact that the language you cite does not say how much braking distance is extended by the ABS relative to what some omniscient rider might do under ideal conditions. And it does not say or remotely hint at how the ABS will perform for average or even skilled riders under uncertain conditions. My comments have been directed toward the comparison that matters, not to influence some hypothetical judge or jury in a negligence lawsuit brought against Suzuki.

Your explanation is very similar to mine. I never said it releases the brake it just reduces pressure inside the brake lines. The studder felt at the controls is pronounced.
Yes, it is pronounced. That is not what I suggest you assess during a maximal deceleration stop. The simple test I suggested is to feel pressure against the heel of your palms on the grips as you approach ABS activation then stop with ABS operating.

Two points I was trying to make... A graph on paper measured in a lab does not reflect in use operation and real world road / traction conditions.
That is both true (trivially) and badly mistaken. Yes, measurements were done in a lab. And yes, they reflect only a subset of real world road/traction conditions (and tire rubber formulations). That is intentional, to get repeatable and comparable results and to keep the cost of the work within reasonable (and grant limited) bounds. But the work I cited [a] was much more seriously done than your casual dismissal implies. I doubt any fair-minded readers would conclude that the measurements underlying the plot I mentioned do not shed considerable light on what happens in the wider world where rubber meets the road.

[a. The U.S. NHTSA (National Highway Traffic Safety Administration) has published The Pneumatic Tire, where (at Figure 11.39, page 458 ) can be found a braking force coefficient versus slip curve for wet asphalt. ]

The graph will change depending on the road surface, condition, debris, weather, temp, etc. The ABS cannot measure the traction directly and it cannot just play against a known experimental graph, it can only measure a difference in spin rates between the tires (partial or full slip).
Of course the curve will change. (In that collection of studies you can find plots for wet and dry pavement, multiple rubber formulations, loading variation and more.) But for the most part, the shape of the traction versus slip curve stays the same even as peak traction and the slip at which it occurs change. The ABS detects when the contact patch has been pushed over to the negatively sloped portion of the curve, whatever its peak value. (That is why ABS is so helpful on frost-covered or slightly oiled road surfaces.)

When a wheel slips ABS needs to back off the hydraulic pressure. It cannot bypass (bypass to where?) it must act inline between the master and slave, there are no recirculation loops. It would have to hold back or block the master cylinder and relieve some downstream pressure on the slave cylinder side in order to achieve its goal. It could accomplish that by isolating the master and oscillating the volume of the down stream brake lines with the pump piston. Is that volume adjustable on the fly? Or is it preset by pump design at the factory? If the latter it has even less chance of perfectly modulating pressure to "ride the hump" of the theoretical traction graph to maximize traction and braking force.
Those are interesting questions. It would be interesting to see answers to them. (From my reading, I understand that there is a recirculation loop in the ABS, where brake fluid let to escape from the brake-cylinder side of the modulator is pumped back to the other side of the modulator. That is why we feel the pulsing.) However, the mechanics of the pressure modulator's operation are not necessary to understand how the pressure modulation causes slip to cycle over the peak of the traction(slip) function.

How tightly it can "ride the hump" would determine how close to maximum traction (and braking force) it can stay. Can the systems of today react fast enough to modulate each ABS pulse based on a direct wheel spin measurement? Or are they still following a preset pulsing curve? The former could ride the hump very tightly, the latter no so much. The former would need to be lightning fast both in processing, actuation, and feedback, perhaps impossibly fast. Chances are the aircraft you mentioned have the most sophisticated ABS at a cost greater than all of your and my vehicles combined.

It is my assertion that the manufacturers know the size of the gap between the theoretical operation you describe and the real world performance achieved by their budget ABS implementation and therefore publish the statement that their ABS can increase stopping distance. I have not yet seen the manufacturers claim that their ABS can decrease stopping distance. They do, however, routinely claim that their ABS can help maintain control during braking by reducing skidding.
Well, they did not have to know the size of the gap to publish their statement which says nothing regarding how much stopping distance might increase. I am perfectly happy to accept that a rider who somehow knows how to keep slip right at the very peak of the traction(slip) function, during a whole stop over unstated roadway conditions, may outperform the ABS-activating stop. I know that if I ever become that rider, even during one stop, the ABS will be still and not hinder my perfect control. But if I go past that traction peak enough, the ABS will bring slip back around the peak, and do it much faster than I could.

In my personal panic stop experience I have ALWAYS experienced a decrease in deceleration while the ABS is active. For example during hard braking I feel (not measure) deceleration, at the point that ABS goes active, I feel less deceleration, every time. Perhaps my vehicles just aren't sophisticated enough...
Your experience differs from mine. However, it is enough to motivate me to get one of the acceleration logging apps for my phone and rerun the experiment with more objective results. Meanwhile, I suggest that you be sure to distinguish jerk from deceleration when assessing ABS efficacy. (I suspect you have noticed that palm pressure on the grips stops increasing when the ABS activates.)
 

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Some very interesting info here. One thing has not been mentioned, however, which may be the most important point.
If the system fails, does it simply revert to normal, non abs brakes, or do you lose brakes completely? Looking at the schematics, both hydraulic and electrical, I think the former case applies. The latter scenario would be very dangerous, from the standpoint of rider safety as well as legal liability for the manufacturer.
 

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Some very interesting info here. One thing has not been mentioned, however, which may be the most important point.
If the system fails, does it simply revert to normal, non abs brakes, or do you lose brakes completely? Looking at the schematics, both hydraulic and electrical, I think the former case applies. The latter scenario would be very dangerous, from the standpoint of rider safety as well as legal liability for the manufacturer.
By design, failure of the ABS results in normal braking. It works by actively modulating the same pressure you exert with the brake lever or pedal. When it does nothing, (such as when little slip is detected), the normal line pressure is simply passed along normally.
 

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KISS

. "... I really don't like the way the rear brakes work in the trails. I'd really like to stop the rear wheel when i'd like to...."
Getting back to Gert's original question: You might consider a plumbing solution than an electrical one.
[KISS - Keep it Simple S....]
 

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OK, I start this with a simple explanation: I do know a bit about ABS. One of my jobs as a technical person at General Motors was to train people on how ABS works, what can go wrong and how to diagnose it. Yes, ABS on a car or truck works pretty much the same as it does on your motorcycle. There has been much written on this thread and most of it is fairly true. I could write a long essay on ABS but will instead make this short and sweet.

ABS helps keep the vehicle under control. It has three basic modes it uses to do this. First, it monitors wheel speeds and looks for a difference between them. As has been written, if it sees the front tire going 30 MPH and the rear tire going slower than that and it sees the brake pedal depressed it knows the rear tire is sliding and it wants to stop this. In order to do this it will do the following (very quickly)
1) hold brake pressure....it will not allow you to add more pressure to the wheel that is locked up or slipping excessively. Should this not fix the situation it will go into its next mode.

2) Decrease pressure....it will reduce the brake pressure on the offending wheel until it sees the speed difference between the front and rear tires fall within the programed parameters. Once the wheels do that the ABS will go to the next mode:

3 Re-apply brake pressure. The system will now start putting pressure back to that wheel as it observes the wheel speed to insure the speed remains where it should be. Note that the system will NOT apply more pressure than what the operator has done with the brake pedal.

As for disabling the system: if the system sees zero rotation from either wheel it will soon set a trouble code and disable the entire system. The brakes will still work but without any modification to brake action. In simple terms: It will operate just as a non-ABS braking system would. I could write much more but that is the short of it.

Final thought: Years ago when motorcycle ABS was new one of the big cycle magazines did a comparison test on ABS systems on motorcycles comparing ABS to non ABS bikes. The results were telling. The short of it was they used three level of riders, professional, average rider and newbie rider. The test was long and exhaustive but their conclusion was simple. They found that on clean dry pavement ABS did not help the professional racer, they were good. As for middle level riders the ABS helped and for the newbie riders it was a big help. On wet pavement the results were interesting. None of the riders, professionals included, could brake as well as the ABS system. The writer's conclusion after all this testing was simple: One should not ask if they should or should not get a bike with ABS. One should just never buy another bike without ABS! It was just that much better.

I will not buy any road vehicle without ABS. I suppose if I were buying a pure off road bike I would not ask it to have ABS due to the type of riding it would be doing. ABS just works. While some people think they are better than the machine real work tests tell a different story. Read up on ABS, its pretty interesting. And for the curious of you out here there is much good information. One particular article is on Wikipedia and touches on some early work on motorcycles. As opposed to some here that say ABS increases stopping distances, well, that depends. On loose gravel or sand or even snow that may be true. But on other surfaces the ABS will stop in a shorter distance.
Good article: https://en.wikipedia.org/wiki/Anti-lock_braking_system#History
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