Abs?

[apopj]

Hey guys,

The other day I was fooling around and grabbed a handful of brakes. I did a stoppie, raising the back tire about a foot off the ground. I asked the mechanic why the ABS II did not kick in and he said something about the back tire coming off the ground, blah blah blah.... Okay, so today I went out and grabbed a bunch of front brake only in gravel. The wheel locked and left a groove in the gravel. Did it again on dry pavement and the front tire brake locked up and left a rubber mark on the ground. If I do a back brake only lock, the wheel glides to a stop without a skid.
My question is, why does the ABS allow the front to lock up, but not the back? I am showing no faults either on the dash or in a computer printout. As a retired Police Motor Officer, I use my front brake alot and don't have a problem stopping, but was just curious about how the ABS is supposed to work? My auto ABS doesn't screech to a stop, was thinking the bike shouldn't either.....
:scratch

Jeff

[deilenberger]

Jeff - what year/model? It makes a difference..

If you're locking the front wheel it really sounds as if your ABS isn't working. That shouldn't happen.

[apopj]

Sorry,

It's an '07 'GS with about 3600 miles on it.... but guys, I've only had it about a month and a half... gimme time to put miles on it.....

Jeff:wave

[FredRydr]

Something's wrong.

Fred
'07 R1200R

[YELLOW_S]

No, nothing is wrong.

The reason the front wheel locks up is because the brakes lock and release the front tire. Instead of just holding it. ABS holds, and then lets go.

The reason the rear will not lock up. Is because there is no weight on it. The rear brakes only makes up 20% (I think) of the braking power. Since when you brake all the weight goes forward.

[FredRydr]

The reason the front wheel locks up is because the brakes lock and release the front tire.If the wheel locks up, ABS is not functioning properly. The very purpose of ABS is to prevent a wheel from locking up.

Fred

[Greenwald]

70% of braking occurs at the front tire, due to weight transfer; 30% occurs at the rear, according to MSF. Use of BOTH brakes means 'combination braking' = 100%.

FredRydr is spot on - an '07 bike with ABS should never lock up it's tire - time for a trip to the dealer under warranty.

[FredRydr]

70% of braking occurs at the front tire, due to weight transfer; 30% occurs at the rear, according to MSF. Use of BOTH brakes means 'combination braking' = 100%.And on the ABS bike, the brake lever on the handgrip is linked to front and rear, and the controller determines the amount of pressure to each. Hence, both brakes are applied by use of the hand lever no matter what.

Fred

[deilenberger]

+1.. the way I test if ABS is working is locking it up in some small hard packed gravel.. if it works you can see the lock/release/lock/release pattern. If it locks and stays locked - something is wrong.

[YELLOW_S]

If the wheel locks up, ABS is not functioning properly. The very purpose of ABS is to prevent a wheel from locking up.

Fred

The brakes grab the rotor and release extremly fast (over 100 times a second). Yes it locks the front tire, but it lets go. And does it till you are stopped.

http://youtube.com/watch?v=a9ssJ1XoqY4

watch the first two minutes of this video.

[YELLOW_S]

And on the ABS bike, the brake lever on the handgrip is linked to front and rear, and the controller determines the amount of pressure to each. Hence, both brakes are applied by use of the hand lever no matter what.

Fred

Not all bikes. I have a 2001 BMW R1100S. With ABS. It (thank god) is not power assisted, or linked. If I pull on the front brake, only the front brake is applied, same if I push on the rear brake.


Yamaha's VFR is the same way, and most bikes. I believe the Gold Wing is not linked either. But I'm not sure.

[FredRydr]

The brakes grab the rotor and release extremly fast (over 100 times a second). Yes it locks the front tire, but it lets go.Yes, yes, yes. But such semantics fail to address the serious brake problem faced by our new hexhead rider. I cannot imagine that the technical one-hundred-times-per-second lock and release is the "locking up" apopj describes here.

Fred

P.S. Poor apopj!! Well, a fifth opinion might be good.

[YELLOW_S]

Sorry, now that I look into it. The 100 times is for a car. Taken off a BMW car.

http://youtube.com/watch?v=vfFq_auOwww

This video shows a person grabbing front, and rear brake of a R1200GS (which if I'm not mistaken is a Hexhead).


This video proves my point that the front tire is locked, and released. Because the front dives, and comes back up.


:edit

If the front tire did not lock up. Then the front would just dive and stay down till the bike comes to a stop.

The reason - If the bike did not grab and let go the of the front. There would be a lot of weight on the front tire, and it might lose traction and fall over.

[Greenwald]

And on the ABS bike, the brake lever on the handgrip is linked to front and rear, and the controller determines the amount of pressure to each. Hence, both brakes are applied by use of the hand lever no matter what.

Fred

As I understand 'linked braking systems,' though squeezing the front brake lever involves 'some' use of both front and rear brakes, not all calipers are in play unless both your right hand and right foot are braking full in unison.

Linked braking allows for casual retarding of your speed at both tires, but is not a replacement for standard combination braking where minimum stopping distance will be critical. Since when surprised or under stress, we will brake like we've trained ourselves by habit, I always practice combination-braking, even for minor stops or traffic delays.

If 'linked brakes' activated by any pressure on the front brake lever results in full, 100% braking of a BMW, please enlighten me, as I am always willing to learn something new, and certainly don't know it all (don't tell my kids that, though!).

[deilenberger]

As I understand 'linked braking systems,' though squeezing the front brake lever involves 'some' use of both front and rear brakes, not all calipers are in play unless both your right hand and right foot are braking full in unison.
That's the system used by Honda and perhaps still Guzzi. AFAIK - not BMW's new system. The new system supposedly uses all the pistons (and calipers that hold the pistons) - with proportioning done by the brake system in response to speed and lever pressure. It's a "smart" system vs a dumb one.
Linked braking allows for casual retarding of your speed at both tires, but is not a replacement for standard combination braking where minimum stopping distance will be critical. Since when surprised or under stress, we will brake like we've trained ourselves by habit, I always practice combination-braking, even for minor stops or traffic delays.

If 'linked brakes' activated by any pressure on the front brake lever results in full, 100% braking of a BMW, please enlighten me, as I am always willing to learn something new, and certainly don't know it all (don't tell my kids that, though!).From what I've read - it does on the newest systems starting in '07.. and brake tests I've seen (I believe in the R1200R review in Motorcycle Consumer News) indicated that your best plan of action for rapid stopping is to use the front lever exclusively for full on braking. If what I've read is correct - the rear brake when operated by the front lever is electronically controlled (and boosted) by the brake/ABS controller.

I rarely use the rear pedal now except for low speed maneuvering in bad traction conditions where I don't want to risk locking and plowing the front end... and even that I suspect I may be being overly conservative... and in those cases, I'm only using the pedal, not the front lever.

[DarrylRi]

As I understand 'linked braking systems,' though squeezing the front brake lever involves 'some' use of both front and rear brakes, not all calipers are in play unless both your right hand and right foot are braking full in unison.

Linked braking allows for casual retarding of your speed at both tires, but is not a replacement for standard combination braking where minimum stopping distance will be critical. Since when surprised or under stress, we will brake like we've trained ourselves by habit, I always practice combination-braking, even for minor stops or traffic delays.

If 'linked brakes' activated by any pressure on the front brake lever results in full, 100% braking of a BMW, please enlighten me, as I am always willing to learn something new, and certainly don't know it all (don't tell my kids that, though!).

I think you're at least confusing the Honda system with the BMW system here, a bit.

The BMW system uses a proportioning valve between front and rear. When you apply the hand lever, all pistons on all brakes are affected. The bike decides how to apportion it front and rear. (The Honda system uses 2 of 3 pistons on the front and 1 of 3 on the rear when you use the hand lever and vice versa for the foot lever.) On the BMW, you can get 100% braking by using just the hand lever hard enough.

[janschunck]

Sorry,

It's an '07 'GS with about 3600 miles on it.... but guys, I've only had it about a month and a half... gimme time to put miles on it.....

Jeff:wave
On a 2007 GS you can disconnect the ABS system. Look at this original german tech page http://www.bmw-motorrad.de/de/de/index.html
It may be you have disconnected your ABS or it has been disconnected by mistake.

[dancogan]

...Did it again on dry pavement and the front tire brake locked up and left a rubber mark on the ground. If I do a back brake only lock, the wheel glides to a stop without a skid....
I don't think all the talk about linked vs non-linked has a thing to do with your problem. With a working ABS system your front tire should not lock up and leave a skid mark on the ground. Generally you can feel the pulsing of the ABS system as it prevents tire skid. JMHO

[Andy VH]

Ok, a basics on ABS is needed here to clarify a lot of arguement.

ALL, meaning, truck, car, train, plane, motorcycle ABS systems work on the principle of comparing actual wheel speed (during braking) to actual vehicle speed. The ABS computer monitors individual wheel speed compared to the vehicle speed it derives from both front and rear wheel speed sensors. Then when braking, if the ABS detects one or both wheels decelerating (at a preset threshold) faster than the vehicle reference deceleration, it engages the ABS control on that wheel.

But, maximum ABS braking effort relies in part on tire contact patch deformation and a preset wheel speed value, up to 20% SLOWER (in other words very slightly sliding)than the actual vehicle reference speed. So for ABS to engage it has to sense the tire is actually sliding beyond that preset value. If NO speed differential is achieved then maximum braking is never achieved. If that near sliding tire threshold is never reached then maximum braking is never reached. That in part, is why a skilled rider on a bike without ABS can produce shorter stopping distances than a bike with ABS. Also, not all ABS control the brakes based on teh exact same threshold values. This was REALLY apparent in the late 80s when the GM/Delco ABS systems preformed MUCH worse than the Bosch ABs systems on the same cars.

When in an ABS braking event, the tire being controlled WILL leave some mark on the surface. And in gravel or loose surfaces, the loose product has a tendency to "dam up" in front of the tire which also causes some sliding even after the ABS has released brake pressure. That is due to brake system hysterisys. Which is basically the time delay to spin up all that tire/wheel/brake discs mass before the ABS attempts another brake application cycle. In those micro-seconds when the tire has not started to again "spin up" there can enough hysterisys to cause some actual tire slide.

Once the bike has slowed enough, say down at the ten to five MPH range, the system hysterisys cannot get the tire to "spin up" again fast enough even after the brake pressure is relaxed. It is not uncommon, at the very end of the stop, for a tire to slide, just a very little bit. This is especially true when braking on loose surfaces like dirt and gravel, again because of the damming effect.

[Greenwald]

So, for clarification purposes, my 2005 R1200RT (with servo-assisted ABS) applies 100% braking authority (both tires) with squeezing of the front brake lever only?

[roadcrave]

Hey::has anyone tried this,, abs on good slick ice, i did this in march outside of winnemuka nevada on a 2003 r1100s, quess what no brakes, actualy the abs kicked in while i rolled right past my turn, I was on ICE...matthew

[Andy VH]

Matthew, I'm curious, how fast, no actually, how SLOW were you going at the time that happened? Your answer may clarify what happened.

Kevin, I'd say check the BMW description in the technical section fo the owners manual. I doubt that you get 100% of "rider applied" brake pressure at both the front AND rear with the linked servo-power brakes. I would assume it is some proportional value of rear brake with front brake application only.

But whatever the proportional value, and no matter how the brakes are applied by the rider, if the ABS system senses wheel lock, it will override whatever the rider is asking for and take over control of only that wheel it senses is near lockup. And since it is a 2-channel (meaning front and rear seperate control circuits) system it can control each wheel totally independant of the other with no "linked" action.

[roadcrave]

This was a weard feeling to apply both front and rear brakes and roll to a stop, like no brakes at all, answer to your question I was slowing from 50mph so id guess around 40mph, it was in the mid 20 degrees that day, i remember seeing a grocery store and just wanted to warm up with a cup of hot coffee...matthew

[FredRydr]

...the front tire brake locked up and left a rubber mark on the ground....

JeffJeff,

Let us know what your mechanic does about this. Don't let it slide (pun intended).

Fred
'07 R1200R

[deilenberger]

Not all bikes. I have a 2001 BMW R1100S. With ABS. It (thank god) is not power assisted, or linked. If I pull on the front brake, only the front brake is applied, same if I push on the rear brake.

Yamaha's VFR is the same way, and most bikes. I believe the Gold Wing is not linked either. But I'm not sure.

This may all be true - but this is also a forum for R1200X bikes, not R11's or Gold Wings or Yamahas.

ALL the R1200- series bikes with ABS have linked brakes.

[deilenberger]

So, for clarification purposes, my 2005 R1200RT (with servo-assisted ABS) applies 100% braking authority (both tires) with squeezing of the front brake lever only?I actually don't understand your question.

If you're asking if the front lever can provide 100% of available braking force at both the front and rear wheel - then the answer is a qualified yes. The qualification is - what do you consider 100% - if it is when the wheel starts to lock up (and the ABS releases it momentarily) - then the answer is yes.

I think you have to clarify what you're asking..

[gened12]

Hey guys,

The other day I was fooling around and grabbed a handful of brakes. I did a stoppie, raising the back tire about a foot off the ground. I asked the mechanic why the ABS II did not kick in and he said something about the back tire coming off the ground, blah blah blah.... Okay, so today I went out and grabbed a bunch of front brake only in gravel. The wheel locked and left a groove in the gravel. Did it again on dry pavement and the front tire brake locked up and left a rubber mark on the ground. If I do a back brake only lock, the wheel glides to a stop without a skid.
My question is, why does the ABS allow the front to lock up, but not the back? I am showing no faults either on the dash or in a computer printout. As a retired Police Motor Officer, I use my front brake alot and don't have a problem stopping, but was just curious about how the ABS is supposed to work? My auto ABS doesn't screech to a stop, was thinking the bike shouldn't either.....
:scratch

Jeff

Hi I owned an 05 1200GS and on many occasions grabbed a handfull of front brake. Never has the front wheel locked up but I could feel the modulation in the braking action. No tire marks either. You have to hold on to stay on the seat :-)

On loose gravel you should not use abs because you WILL highside with a handfull of front brake since you will most likely dig in the front wheel.

my 2 cents worth,

Cheers

Denis R1200RT:whistle

[Andy VH]

Sooo,...Matthew you are saying the bike came to a stop when you applied the brakes, or are you saying you applied the brakes but felt no braking action? Not sure what you mean.

On glare ice, near perfectly smooth, the braking sensation will be very slight, and you'd probably feel the ABS action more than the braking action. But it would take little brake lever application to get the ABS to engage.

I know car and truck ABS systems in the past worked on a 20% tire "slip" ratio even with ABS action. Meaning, the ABS controlled tire was actually "slipping" at a speed 20% slower than the actual vehicle speed during an ABS stop. The 20% slip ratio produced the best braking and shorter stopping distance. Without the slip ratio the braking distance during an ABS event would be much longer. This also meant that a good ABS stop on dry pavement WILL leave a tire mark, every time.

But, I doubt that cycle ABS systems work on the same 20% slip ratio, since a slip ratio that high may cause instability. But a lower slip ratio would also mean longer braking distance for ABS stops versus normal braking stops. I would guess a slip ratio closer to 10% would be reasonable. That would also mean less likely tire marks on the pavement during an ABS stop.

[Greenwald]

I actually don't understand your question.

If you're asking if the front lever can provide 100% of available braking force at both the front and rear wheel - then the answer is a qualified yes. The qualification is - what do you consider 100% - if it is when the wheel starts to lock up (and the ABS releases it momentarily) - then the answer is yes.

I think you have to clarify what you're asking..

Took a GOOD look at my owner's manual today. It informs me that my 2005 R1200RT has integrated ABS, i.e. both front and rear brake will be fully activated with squeezing the front brake lever aggressively. Pressure on the rear brake pedal activates only the rear brake, which I use liberally in the myriad of maneuvers I learned as a Motor Officer.

So - today, I have learned something - my integrated ABS requires only front brake application to engage. Now of course, this dilema begs another question: since I will continue to use combination braking (never know when a different bike you may be riding is not integrated like a BMW), will the rear brake pedal pressure, in addition to the front brake lever-activated integration, cause excessive wear on the rear brake pads???

Thanks for the feedback.

[roadcrave]

Andy, Yes the brakes barely engaged, even though I was on them pretty hard, At firstI thought my brakes Iced over, but actually the ABS kept the wheels rolling by barely activating the pads...matthew

[Andy VH]

Hi Kevin. I doubt your braking actions will cause excessive rear brake pad wear. I'm assuming this, but knowing BMW logic, if you apply the rear brake in addition to the front brake (like we always used to do) I'd bet the rear brake pedal overrides the integrated function of the front brake lever.

If it didn't, and the two control applications were cumulative, then rear tire lockup would be even more prevalent. That would be illogical to good motorcycle thinking in BMW logic.

[Greenwald]

OK - your answer makes sense. Will still adhere to combination braking, since I want that 'habit' ingrained into motor-memory. I jump on too many other makes (my son's '07 ST1300, rentals and a buddy's non-ABS Triumph Sprint ST) to be constantly adjusting my braking protocols. Not safe.

Enjoy our ferocious winds today - realing howling out there!

[kbasa]

Not all bikes. I have a 2001 BMW R1100S. With ABS. It (thank god) is not power assisted, or linked. If I pull on the front brake, only the front brake is applied, same if I push on the rear brake.


Yamaha's VFR is the same way, and most bikes. I believe the Gold Wing is not linked either. But I'm not sure.

VFR and Gold Wing = Honda.

[kbasa]

Hey guys,

The other day I was fooling around and grabbed a handful of brakes. I did a stoppie, raising the back tire about a foot off the ground. I asked the mechanic why the ABS II did not kick in and he said something about the back tire coming off the ground, blah blah blah.... Okay, so today I went out and grabbed a bunch of front brake only in gravel. The wheel locked and left a groove in the gravel. Did it again on dry pavement and the front tire brake locked up and left a rubber mark on the ground. If I do a back brake only lock, the wheel glides to a stop without a skid.
My question is, why does the ABS allow the front to lock up, but not the back? I am showing no faults either on the dash or in a computer printout. As a retired Police Motor Officer, I use my front brake alot and don't have a problem stopping, but was just curious about how the ABS is supposed to work? My auto ABS doesn't screech to a stop, was thinking the bike shouldn't either.....
:scratch

Jeff

How fast were you going? I believe that at very low speeds, ABS will not kick in. I've seen a guy do stoppies on an ABS equipped R11RT, but he had to "sneak up on it", in his words, and nail the brakes at something around 5mph.

[FredRydr]

...will the rear brake pedal pressure, in addition to the front brake lever-activated integration, cause excessive wear on the rear brake pads?Yes. At least I think so, but BMW is quite content with selling lots of rear brake pads.

Fred
'07 R1200R

I should edit this because my experience with excessive rear pad wear was on my R1150R with ABSIII, not my current R1200R with the new generation ABSII. I will just have to wait and see with the latter bike; I'm at 11,000 miles.

[Greenwald]

Yes. At least I think so, but BMW is quite content with selling lots of rear brake pads.

Fred
'07 R1200R

You may be right - had to have my rear brake pads replaced at 18,000 miles on a new R1200RT.

[Andy VH]

Kbasa, what you mention has to do with the histerysis threshold of ABS equipped vehicles. Though I bet the histerysis in the brakes of a motorcycle is very low compared to a car. But at lower speeds the ABS really cannot effectively cycle the brake action on-off quickly enough to maintain control.

On my 94 R1100RSA I have noticed that right near the end of a purposeful ABS stop the front tire may skid very briefly.

[FredRydr]

...the histerysis threshold of ABS equipped vehicles. Though I bet the histerysis in the brakes of a motorcycle is very low compared to a car.So, WTF is histerysis? Tossing out esoteric terms like this may be fun, but not for everyone else who haven't a clue.

Fred
'07 R1200R

[DarrylRi]

http://en.wikipedia.org/wiki/Hysteresis

Hysteresis is a property of a system to tend to maintain a current state beyond a nominal trigger point. Sort of a Newton's second law for systems.

For example, the thermostat for a heater might have a set point of 72F, but it will run until the house is actually at 73.5, shut off, and not come back on until the house drops below 70.5.

In an ABS context, the ABS might tend to freewheel a bit longer than the point at which the formerly locked wheel is rolling at speed again; and then it might allow the brakes to keep the wheel locked a bit longer than the point at which it determines that the wheel is locked. The hysteresis in this system would have to be carefully set so that a loss of control doesn't occur.

[Andy VH]

Another way to think of histerysis is just plain old physics. During an ABS braking event, the braked wheel gets VERY close to actually stopping rotation. Every time it nearly stops rotating, it has to "speed up" again when the ABS control has released the brake pressure, in order for that wheel to match the actual bike speed. The time delay in that micro-second for the wheel to spin-up is histerysis.

Think of it in "mass" terms this way. A bike with a skinny front tire/rim and a single brake disc, has much less mass than the wide rim/tire dual 300mm disc braked wheels common to our bikes. If the same ABS control were applied to each bike, the one with the less mass on the front tire will "spin up" much quicker than the one with the higher mass front tire. The skinny/lighter wheel has much less inherent histerysis.

Something like a semi-truck wheel/brake system has much higher histerysis than does the light wheel/brake system of a motorcycle. That's one reason ABS on a big heavy truck has much slower reacting ABS than the system on our BMWs. The cycles per second rate of ABS control on a truck may be about five cycles per second at best, while on our bikes it may be ten cycles per second.

There is also the histerysis effect of the brake system plumbing and hydraulics, but that's not worth discussing for the mimimal effect it has.