ABS behavior question? - K-Bikes.com - Excellence in Motion
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post #1 of 11 (permalink) Old Dec 21st, 2007, 5:51 pm Thread Starter
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ABS behavior question?

I decided to go out today (wet deserted parking lot) and see how my ABS feels and reacts. I have a K1200 R. I was a little surprised to find it lock and release in such a pronounced manner. My car does the same thing but at a more rapid pace like a machine gun. The bike lock and release was significantly more lethargic.
I was wondering if this was consistent with your experiences.
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post #2 of 11 (permalink) Old Dec 21st, 2007, 9:34 pm
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ABS Behavior

Yep, that's how it works. Cars use pumps that take over brake function until lock up is no longer experienced or you apply less pedal pressure. BMW's ABS simply removes line pressure. The result is what you felt.
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post #3 of 11 (permalink) Old Dec 22nd, 2007, 1:00 pm
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I have had my ABS kick in a couple of times. Mine feels like a quick stutter.

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post #4 of 11 (permalink) Old Dec 24th, 2007, 3:43 pm
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There was a discussion recently about the effect of the (slow) ABS action when you aren't going that fast and need to stop in a short distance.

I think I came to my own conclusion that there are some situations when the ABS isn't too clever at adapting to very slow short distance braking. So if it kicks in, I might be better off quickly releasing and re-applying the brake less hard, rather than suffer the consequence of the brake being removed by the ABS whilst I'm still moving forwards with no brakes into a hard object. I've only ever had the ABS come on in a wet road emergency stop from 50 mph, it felt wierd but the bike stopped upright. I never knew if I could have stopped it better without ABS. I like the idea of 'tapered progressive' release, but our systems use a 'modulator' i.e on and off, where the key factor is how they control the on/off ratio with speed, if at all. I can't imagine it being that clever.

I also learned that the GS's can turn off the ABS, which for short sharp stopping and bike control is probably why you have the option.



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post #5 of 11 (permalink) Old Dec 25th, 2007, 3:37 am
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This was my first bike with ABS, although I have driven many cars over the years with ABS systems.

I went out one day to some deserted roads to see how the ABS reacted to some 'emergency' stops from around 80mph. I found that the way the ABS is set up, the only objective is to stop the wheels from locking up, which in turn greatly increased the distance to stop. I think due to this safer setting there is less transfer of weight to the front tyre therefore the brakes cannot be applied as hard reducing the stopping distance.

On car systems where the car does not fall over if a wheel is locked the set up can be far more aggressive and allow the wheel to run nearer to lock up, maximising breaking effort.

So on the bike I ride it as if I had no ABS, apply the brakes hard but not hard enough to trigger the ABS.

Unless, in extreme emergency situations when you find yourself in a totally unanticipated situation, the final resort is the ABS
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post #6 of 11 (permalink) Old Dec 25th, 2007, 8:03 am
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Try this:

Go out on a deserted highway with good pavement and try the same thing- Find a place with plenty of sight distance and make a number of stops from higher speeds-up to say, 80-90mph. See what you experience. Do the same for dry conditions- Simply put it is potentially a life saving understanding of what you and your machine can do to avoid the "big one" Understand your limitations and exploit as much fun out of it as you can. That's my philo. on that- Pulsations in the brakes are ABS. Happy Holidays
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post #7 of 11 (permalink) Old Dec 25th, 2007, 10:24 am
 
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I often practiced my panic stoping on my 04'KGT and found the pulsing to vary depending on road surface conditions and speed. Often times the slower I went, the more pronounced 'on/off' jerkey it was, and a higher speeds it smoothed out a bit. For the record, it takes a looong distance to stop the GT beast at triple digit plus speeds ABS or not!
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post #8 of 11 (permalink) Old Dec 25th, 2007, 6:31 pm Thread Starter
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Thank you everybody for the responses. I tried my ABS at higher speeds 70mph plus and it did respond more like I was used to with a faster studder. It was just slower at cycling at the 20mph speeds I was trying it at. I still get the eerie ghost ABS sometimes over rough pavement. Anyway good advice trying it out at the higher speeds.

I sure appreciate everybodys time.
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post #9 of 11 (permalink) Old Jan 2nd, 2008, 11:44 am
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It is still possible to do a stoppie with the BMW ABS, almost at will with the older version on the R1100RSA.

I have elevated the rear on my 07 K1200GT, Bambi's Dad decided to jump out in front of us on the expressway when we were doing about 70, (2 up). My riding partner, said he saw brake lights, 6" of air under the tire and then Bambi's Dad. Damn deer had to stop and look at us until we were stopped before it moved. At least the rest of his family was not along.

At very slow speeds you can lock the front, aka at a crawl < 2 mph, as you move forward at a stop sign.

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post #10 of 11 (permalink) Old Jan 2nd, 2008, 6:17 pm
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When a tyre is on tarmac, it requires a certain amount of force to skid.

Once a tyre is skidding, it requires a lower force to keep skidding.

This is due to the change of coefficient of friction between the two cases.

As an aside, different surfaces have different coefficient. Ice is far lower, but skidding on ice has an even lower coefficient of friction, for example.

ABS works by preventing the wheel from skidding and keeping it rolling with the brakes applied. In doing so, its able to provide more braking force, stopping you sooner.

Just to clarify from an engineering perspective. There are safety benefits that can be drawn from this (for example, locking the rear wheel and letting it skid out can cause a flip of the bike when grip is re-established).
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