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Old 10-07-2011, 11:15 AM   #8851
Mercury264
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Originally Posted by Yossarian™ View Post
ABS releases brake pressure when it senses the wheel locking up. Wheels lock up more easily under low braking pressure on loose surfaces, which means that the ABS essentially disengages the brakes. Couple that with a steep downhill and the rider must now negotiate the run without benefit of usable brakes.

It's fun to freewheel down a steep rocky hill on a 30# mountain bike; not so much fun on a 450# motorcycle.
But if a wheel is locked up, how can it provide any braking force ? Or am I missing the point that on tarmac that is true but on gravel it's not - i.e. due to the gravel road surface, even a locked up wheel can provide some braking force - but then if that's true, can it provide MORE braking force than you can get with the wheel turning ?

Just trying to learn here - this is the first bike I've had with ABS and I hear all the time about dis-engaging the ABS while on dirt but I want to try and find out why that's the case.
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Old 10-07-2011, 11:17 AM   #8852
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Originally Posted by Yossarian™ View Post
ABS releases brake pressure when it senses the wheel locking up. Wheels lock up more easily under low braking pressure on loose surfaces, which means that the ABS essentially disengages the brakes. Couple that with a steep downhill and the rider must now negotiate the run without benefit of usable brakes.

It's fun to freewheel down a steep rocky hill on a 30# mountain bike; not so much fun on a 450# motorcycle.
They don't disengage. They pulse leaving you the ability to still handle the bike. Imagine that same scenario with a rear tire sliding and now starting to turn you sideways. If it's never happen to you let me fill you in, It sucks! I have had zero abs issues on gravel with my XC. The pulse seems perfect and helps a ton in my opinion.
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Old 10-07-2011, 11:20 AM   #8853
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Originally Posted by Mercury264 View Post
But if a wheel is locked up, how can it provide any braking force ? Or am I missing the point that on tarmac that is true but on gravel it's not - i.e. due to the gravel road surface, even a locked up wheel can provide some braking force - but then if that's true, can it provide MORE braking force than you can get with the wheel turning ?

Just trying to learn here - this is the first bike I've had with ABS and I hear all the time about dis-engaging the ABS while on dirt but I want to try and find out why that's the case.
No problem, I'll be happy to help with my limited knowledge.

A locked wheel will always provide *some* measure of braking force. In situations with hard surfaces, it's usually significantly less force than braking with the wheel not sliding; static vs. dynamic coefficients of friction.

On gravel/dirt, though, a locked wheel builds up a little ramp of loose stuff in front of the contact patch, which actually provides a greater braking force than can be accomplished with strictly dynamic friction. As the tire slides the force is dissipated through moving all of the little debris away from the path of the tire.

Try it with a bicycle. Lock the the rear brake and just try dragging it through a sand pit. It takes a lot of effort!
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Old 10-07-2011, 11:24 AM   #8854
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They don't disengage. They pulse leaving you the ability to still handle the bike. Imagine that same scenario with a rear tire sliding and now starting to turn you sideways. If it's never happen to you let me fill you in, It sucks! I have had zero abs issues on gravel with my XC. The pulse seems perfect and helps a ton in my opinion.
I'm not advocating the disabling of the ABS for all off-pavement operation, so please don't think I'm anti-ABS. If I have a very steep downhill grade off pavement to negotiate, though, I'll turn the ABS off every time.

I cannot count the number of times I've had to negotiate a very steep trail descent; it is usually much easier if I can do so by locking the rear wheel and letting it drag. (Not on the Tiger, mind you, but more dirt-oriented machines.) The force of gravity easily overpowers even engine braking in 1st gear on steep inclines.

Here is an interesting read: http://www-nrd.nhtsa.dot.gov/pdf/Esv/esv16/98S2W36.PDF

I understand that not all ABS systems are identical. Still I think it's good to be able to disable one when needed.
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Old 10-07-2011, 11:34 AM   #8855
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Originally Posted by Mercury264 View Post
But if a wheel is locked up, how can it provide any braking force ? Or am I missing the point that on tarmac that is true but on gravel it's not - i.e. due to the gravel road surface, even a locked up wheel can provide some braking force - but then if that's true, can it provide MORE braking force than you can get with the wheel turning ?

Just trying to learn here - this is the first bike I've had with ABS and I hear all the time about dis-engaging the ABS while on dirt but I want to try and find out why that's the case.
Somewhere on Youtube is a vid of a BMW GS going down a rocky slope that will answer your question with alarming clarity. Fortunately, nobody got hurt, but the footage really is a testament to why you should disengage ABS off road, at least on the BMW.
edit: Didn't find it after digging around, but I have seen the video linked here before.
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Old 10-07-2011, 11:39 AM   #8856
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What happened ?

I don't understand why ABS is so bad in gravel type situations ? Can anybody fill me in
Quote:
Originally Posted by Yossarian™ View Post
ABS releases brake pressure when it senses the wheel locking up. Wheels lock up more easily under low braking pressure on loose surfaces, which means that the ABS essentially disengages the brakes. Couple that with a steep downhill and the rider must now negotiate the run without benefit of usable brakes.

It's fun to freewheel down a steep rocky hill on a 30# mountain bike; not so much fun on a 450# motorcycle.
Not just gravel or loose surfaces but a steep cobblestone street can be interesting as well. Think small town in the Alps. Good luck NOT running straight into that building at the end on any BMW....

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Old 10-07-2011, 12:17 PM   #8857
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Originally Posted by fullmonte View Post
Somewhere on Youtube is a vid of a BMW GS going down a rocky slope that will answer your question with alarming clarity. Fortunately, nobody got hurt, but the footage really is a testament to why you should disengage ABS off road, at least on the BMW.
edit: Didn't find it after digging around, but I have seen the video linked here before.
Here it is:


This one's a good demonstration too (first run is ABS on, second is ABS off and rear brake only, third is ABS off, rear brake, and modulated pressure on the front brake):


--mark
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Old 10-07-2011, 12:29 PM   #8858
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I'm not advocating the disabling of the ABS for all off-pavement operation, so please don't think I'm anti-ABS. If I have a very steep downhill grade off pavement to negotiate, though, I'll turn the ABS off every time.

I cannot count the number of times I've had to negotiate a very steep trail descent; it is usually much easier if I can do so by locking the rear wheel and letting it drag. (Not on the Tiger, mind you, but more dirt-oriented machines.) The force of gravity easily overpowers even engine braking in 1st gear on steep inclines.

Here is an interesting read: http://www-nrd.nhtsa.dot.gov/pdf/Esv/esv16/98S2W36.PDF

I understand that not all ABS systems are identical. Still I think it's good to be able to disable one when needed.

Im not thinking anyone here is anti-ABS. This is my first bike with ABS as well and I was VERY against it. I am no longer against it and find it a great tool. Some will never buy into it! I do agree with your down hill dragging scenario. I was just saying that it doesnt disengage the brake. Its an on-off pulse that should technically stop you faster in almost all circumstances. I have found it very interesting that some inmates have stated that other bikes they have ridden with ABS are almost dangerous to ride. I also can't help but to point out that ABS is engaged most of the time when you are using the break with great force and you have no traction. The answer may not be ABS issue but rider issues. How about throwing out the idea of not slamming on your brakes, but putting them on just to the point of slipping or kicking in the ABS. In my opinion ABS is intendend to keep you safe in an OH SHIT moment. It is not a crutch to make your bike handle better in all circumstances... Like it or not thats my opionion and this is how I utilize my brakes/ABS for my Tiger. If were talking offroad dirtbike riding, then its an entirely different story! CHEERS
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Old 10-07-2011, 12:56 PM   #8859
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Here it is:


This one's a good demonstration too (first run is ABS on, second is ABS off and rear brake only, third is ABS off, rear brake, and modulated pressure on the front brake):


--mark
This makes me want to do the same set up with the tiger. The first video is a terrible example. He goes half way down the hill with no feet even on the pegs, so thats telling me that he only has front break applied (maybe). He was doomed to start with. Without ABS and only front break applied he would have tucked the front end and yard sailed over the handle bars! ABS may have actually save this guy from breaking his neck.
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Old 10-07-2011, 01:31 PM   #8860
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This makes me want to do the same set up with the tiger. The first video is a terrible example. He goes half way down the hill with no feet even on the pegs, so thats telling me that he only has front break applied (maybe). He was doomed to start with. Without ABS and only front break applied he would have tucked the front end and yard sailed over the handle bars! ABS may have actually save this guy from breaking his neck.
I agree, that is definitely not a good example of how things could have happened.

In the real world, we have some such kamikaze riders out there. In those cases, the bikes have to be set up from the manufacturer for the dumbest least prepared riders amongst us. Not sure what is best in terms of brakes.
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Old 10-07-2011, 02:18 PM   #8861
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I agree, that is definitely not a good example of how things could have happened.

In the real world, we have some such kamikaze riders out there. In those cases, the bikes have to be set up from the manufacturer for the dumbest least prepared riders amongst us. Not sure what is best in terms of brakes.
I'm also a BMW owner and the ABS on the Tiger is much more forgiving in the soft stuff.
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Old 10-07-2011, 02:33 PM   #8862
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Here it is:
This one's a good demonstration too (first run is ABS on, second is ABS off and rear brake only, third is ABS off, rear brake, and modulated pressure on the front brake):

--mark
Based on the second vid ABS blows chunks in the dirt.
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Old 10-07-2011, 02:43 PM   #8863
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Don't forget the fun factor i like to lock up the back wheel on fire roads going into a corner
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Old 10-07-2011, 03:09 PM   #8864
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I'm also a BMW owner and the ABS on the Tiger is much more forgiving in the soft stuff.
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Based on the second vid ABS blows chunks in the dirt.
Don't generalize about ABS in the dirt. BMW ABS blows chunks in the dirt as demonstrated in those videos. Some ABS is very good in the dirt. Yamaha's new system on the Super Tenere is excellent in the dirt with NO reason to turn it off for everyday riders. Looks like the Tiger's system works OK off road as well.

Problem is dual sport riders have been brain washed by living with BMW's system for so long that they simply parrot that you have to turn off ABS in the dirt. Bullshit. Just test the ABS on YOUR bike and see what it does. I have ABS on my Honda CBF and have tried it on gravel roads and you have a surprising amount of braking available on gravel roads. It takes a pretty good squeeze to get the ABS to kick in and yes on the CBF I get that free wheeling feeling when it does but this is a purely road oriented bike.
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Old 10-07-2011, 03:14 PM   #8865
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No problem, I'll be happy to help with my limited knowledge.

A locked wheel will always provide *some* measure of braking force. In situations with hard surfaces, it's usually significantly less force than braking with the wheel not sliding; static vs. dynamic coefficients of friction.

On gravel/dirt, though, a locked wheel builds up a little ramp of loose stuff in front of the contact patch, which actually provides a greater braking force than can be accomplished with strictly dynamic friction. As the tire slides the force is dissipated through moving all of the little debris away from the path of the tire.

Try it with a bicycle. Lock the the rear brake and just try dragging it through a sand pit. It takes a lot of effort!


Thanks. I figured that's what it was WRT gravel roads.
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