abs and locking up the front - BMW Luxury Touring Community
 
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post #1 of 14 Old Dec 11th, 2006, 9:43 am Thread Starter
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abs and locking up the front

This is my first ABS equipped bike, on a few occasions I have applied the front brakes to the point of wheel lockup,(tire howling). I generally freak out at this point and let up pressure or add rear brake. Road conditions seem normal with no obvious signs of fluid or debris. Should I be patient and see what happens next? I'm fearful the next step could be crashing! BTW- No odd noises or trouble lights appearing. Thankfully, I have yet to require a full on emergency stop but would like to know if this is normal behaviour before an actual one confronts me.
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post #2 of 14 Old Dec 11th, 2006, 9:47 am
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Quote:
Originally Posted by alanforn
This is my first ABS equipped bike, on a few occasions I have applied the front brakes to the point of wheel lockup,(tire howling). I generally freak out at this point and let up pressure or add rear brake. Road conditions seem normal with no obvious signs of fluid or debris. Should I be patient and see what happens next? I'm fearful the next step could be crashing! BTW- No odd noises or trouble lights appearing. Thankfully, I have yet to require a full on emergency stop but would like to know if this is normal behaviour before an actual one confronts me.
Try it out at VERY low speed on grass or gravel, and gradually increase your speed as your confidence grows. It is quite a weird feeling stopping quickly on slick surfaces.

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post #3 of 14 Old Dec 11th, 2006, 9:59 am
 
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Good question

Practicing emergency stops is essential. On gravel, on wet pavement, and on dry pavement. From a variety of speeds as well. Obviously, start slow and go from there. I think every rider should know what it feels like to apply full brakes (front and rear) on their bike at 55 mph, whether it's a BMW w/ ABS or a scooter w/o ABS. The more you practice the less of a surprise it will be the day you really need to do it.
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post #4 of 14 Old Dec 11th, 2006, 12:14 pm Thread Starter
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I feel as though I have a pretty decent understanding of braking, having roadraced for 12 years. I also believe that practice on a new bike is essential to learning it's behaviors. What I'm not as sure of, is the manner in which the BMW system operates. If the system allows full lockup, I would presume at a point a rapid cycling of brake pressure is employed. I know on a non ABS bike maximum braking effectness has been exceeded at the point of loss of traction,(skidding). It just seemed to me that the front tire locked up for a few feet on two occasions,(not wet, no debris, good asphalt), with no hint of any ABS related function coming into play. Does this sound normal?

What I would like to avoid is ending up in a wad, explaining that I was experimenting with the dynamics of LT brakes, "I'll skid a bit more dear, I'm sure the ABS will kick in any moment............."
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post #5 of 14 Old Dec 11th, 2006, 12:38 pm
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If in doubt have dealer check function.....then go practice like Joe suggests.

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post #6 of 14 Old Dec 11th, 2006, 1:08 pm Thread Starter
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O.K.- practice and dealership checkup, I'll rephrase the question counselor: What has been YOUR experience with the LT ABS at the braking threshold, specifically the front brake?
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post #7 of 14 Old Dec 11th, 2006, 1:41 pm
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Properly operating ABS system should "never" lock up and slide the wheel. That's the whole point of the thing. At least in the direction of rotation, and ignoring lateral forces.... (etc, etc, disclaimer for not being an engineer, etc)

Now, is the 'howl' slide or hard brake noise?

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post #8 of 14 Old Dec 11th, 2006, 1:53 pm
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Quote:
Originally Posted by alanforn
O.K.- practice and dealership checkup, I'll rephrase the question counselor: What has been YOUR experience with the LT ABS at the braking threshold, specifically the front brake?
You should feel the ABS grab and release on a repetitive basis. It kind of feels like you're actually speeding up slightly during the release, but that's just in relation to the hard stopping power when the brakes kick in again. It's a bit disconcerting, but less so than sliding down the road on your side. Low traction or wet pavement will cause this, as will hard braking on bumpy or rippled roads.

The ABS is designed to deactivate at real low speeds (something like 3 mph or less). Otherwise you could never come to a complete stop.

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post #9 of 14 Old Dec 11th, 2006, 2:04 pm Thread Starter
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Quote:
Originally Posted by Zotter
Properly operating ABS system should "never" lock up and slide the wheel. That's the whole point of the thing. At least in the direction of rotation, and ignoring lateral forces.... (etc, etc, disclaimer for not being an engineer, etc)

Now, is the 'howl' slide or hard brake noise?
The howl is rubber singin,(lockup).
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post #10 of 14 Old Dec 11th, 2006, 5:57 pm
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Quote:
Originally Posted by alanforn
O.K.- practice and dealership checkup, I'll rephrase the question counselor: What has been YOUR experience with the LT ABS at the braking threshold, specifically the front brake?
This is what I can tell you about my '04. The harder, and less progressive the front brake application is, and the tire will skid before the ABS kicks in. We're talking milliseconds.

Gravel - few inch slide and then released by the ABS

70-80 mph - near panic application and I get a front tire chirp and then a release by the ABS.

Bumps and rough pavement - same as above


ABS systems sense wheel speed. If the ABS kicks in before zero wheel speed you've lost brake effectiveness. So IMO, there will be a nanosecond of lockup before release and that is what I experience on the LT.

I have never done a high speed - grab the brake full hard - and leave it there to see how many pulses I get.

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post #11 of 14 Old Dec 11th, 2006, 6:26 pm
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Originally Posted by bowlesj
I have never done a high speed - grab the brake full hard - and leave it there to see how many pulses I get.
You ought to try it, more fun than goosing a bull in a squeeze chute. Just remember to keep your head up and eye's to the horizon.



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post #12 of 14 Old Dec 11th, 2006, 7:58 pm
 
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Originally Posted by alanforn
O.K.- practice and dealership checkup, I'll rephrase the question counselor: What has been YOUR experience with the LT ABS at the braking threshold, specifically the front brake?
Neither my ex-LT or my current GT would lockup the front tire for more than a few inches...even in gravel. If you're getting full lock, I don't think your ABS is working properly. Perhaps the sensor is out of spec. That's a simple check.
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post #13 of 14 Old Dec 12th, 2006, 7:39 pm Thread Starter
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Thanks to all for the feedback, will check it out
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post #14 of 14 Old Dec 12th, 2006, 7:56 pm
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Lockup

I have done some panic stops for practice anywhere from 45 to 55 and not had a lock up.
Only time I did was when I hit gravel on the berm doing a quick emergency stop when someone ran out of gas in front of me going 55 and swerved to miss them then stopped, but it skidded for maybe for a second or two before it corrected.

Have yours checked out by the dealer with the computer to make sure your ABS is working correctly and once it is do some more panic stops for practice
and have fun

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