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James R. Davis
 Administrator
14909 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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 Posted - 09/25/2003 : 4:26 AM
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I have been rather steadfast in my refusal to accept ABS as a worthwhile addition to my motorcycle - not because I don't think it works, but because I think proper braking technique is more effective - and it is an expensive option.
However, I have also been virtually rabid in my admonishing to NEVER aggressively use your rear brake because of how easy it is to lock that brake and place yourself in a potentially deadly situation as a result.
Somewhere there is a compromise - that is, ABS is a godsend for inexperienced riders or those who simply will not practice braking techniques so that they find themselves having to 'learn' their braking limits in a panic situation. In those cases the expense of the option is of no concern.
So, let me ask those of you that have ABS, or those of you who REALLY understand how it works, for your opinions.
It is my understanding that ABS is not designed to help you stop in the quickest time and shortest distance. Rather, it is designed to help you avoid locking the rear brake. It does that by sensing when the rear wheel is spinning at a different (slower) rate than the front wheel is spinning (i.e., it is skidding.)
In such a case it releases brake pressure and allows the rear wheel to regain its traction, then QUICKLY restores braking pressure. In the past the speed with which the system responded was relatively slow - and the result was that there was NO BRAKING from the rear wheel for a relatively long time. Clearly that resulted in less than optimal braking, but it did avoid loss of control from a locked rear brake.
Subsequently these systems have been built with incredibly fast computers and sensors so that today's ABS systems no longer have that as a glaring deficiency. Still, I wonder. That is, if HALF the time (no matter how short the intervals) there is no braking pressure on the rear brake when the rear wheel is close to skidding then doesn't that mean that there is, on average, only 50% braking near its limits?
Granted that the physical reality is that you cannot remove brake pressure instantaneously and that therefore there is SOME (fading) brake pressure even in the half cycle where the system has 'removed' brake pressure, what is the effective braking rate over time? Is it close to 50%? More like 75%? Very close to 100%? (The closer to 100% the closer to optimal stopping performance.)
Anybody have any real-world experience and data to share with us?
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/25/2003 : 9:00 PM
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Maybe I'm a bit old fashioned but from what I know about ABS systems I would prefer not to have them on my bike or cars. Why?
(1) Increased and unnecessary complication to what should be a simple system with minimum points of failure.
(2) I like to "drive/ride" my vehicles instead of just being in the drivers/riders seat. I would rather be able to control what's going on under me than rely on some "black box".
(3) ABS systems as stated here do not improve braking performance and in some cases increase stopping distances. Their only advantage is the keep the wheels "steerable" in a panic stop.
This is a debatable advantage. If its a "panic stop" then you are already in a bad situation where you haven't been paying attention to the road conditions.
Furthermore, in these situations there most likely is nowhere to steer to!. Lanes are full of traffic, you are in a narrow cutting, guides rails each side, or you just plain panic and don't steer out of trouble.
If you can steer out of trouble then its not a "panic situation anyway and you have anticipated problems in advance and you don't need ABS anyway. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/25/2003 : 9:24 PM
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Jim,
As you know, I don't have ABS. But I have taught enough ERCs to make judgments on stopping distances between ABS equipped BMWs and other motorcycles without ABS. I would opt for the ABS if it were available on the model bike I was considering.
Sorry, even a pro has a hard time keeping up with the changing traction conditions on the street.
Do I think ABS is a good thing? Yep. Does it only work on the rear wheel? Don't think so. I will check this out at a later date in the near future.
// OB |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/25/2003 : 10:20 PM
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(From: Scooter) Interesting question. Some other points to ponder.
1) On today's automobiles with ABS, in most situations, the stopping distances at maximum braking have not changed at all. This is with professional drivers doing the testing. One example was a comparison test on a Corvette, ABS on and ABS off. Stopping distances from 60 were within 5 feet with professionals doing the driving. I suspect that the newest ABS motorcycles would yield the same results. Meaning that a pro won't gain or lose stopping power, but an average rider will probably gain with ABS. One note I will add is that automotive ABS can greatly extend the stopping distances on mixed surfaces, stopping power is limited by the wheel with the LEAST traction. Two wheels on ice and 2 on dry pavement will have an ABS vehicle taking 3 or 4 times the distance to stop as a non ABS vehicle would.
2) I believe that BMW is using, or working on, a system that uses acceleration rate algorithms to sense wheel lockup. When a tire skids, the wheel normally changes it's rate of rotation quickly, i.e.. it stops turning. By using an acceleration rate algorithm to sense when the rate of change in wheel rotation spikes, you do not need to use another tire to sense lockup. This means that you can have an ABS system that is single point and can tune the ABS action for each individual wheel. A system like this would eliminate the mixed traction problem that cars with ABS have. This type of system could lead to the car pulling toward the high traction side in a stop, however.
I have tended to be as skeptical as you are about ABS. My cars don't have it and I saw a superb example of the mixed traction problem last winter, the driver beside me went through a red light I stopped easily for. I know he was trying to stop, the brake lights were on the whole time I was watching, and I could see the panic on his face as he passed by me.
However, seeing BMW demonstrate their new system has given me second thoughts. BMW's new system worked extremely well in this demonstration and they claim you won't notice it working at all. Braking in the rain always makes me very nervous, you never know what is under that water, oil grease, etc. Having ABS in the rain would help alleviate that worry.
My hope is that someday a completely independent ABS system will be available at a reasonable cost. Linked brakes are something I am too old fashioned to accept right now and the ABS systems that I am aware of are all linked. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/26/2003 : 8:21 AM
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For those of you who do not know, OB (Bill) is an MSF instructor (or whatever they are called now) and we have shared asphalt many times with our motorcycles. Bill has exceptionally fine control of his motorcycle at all times. Indeed, when he comes to my house to meet with me before a ride there is a narrow area behind my parking area that Bill invariably uses to 'practice' slow tight turns on while he is waiting for me or any others that are going on our ride. He leans his bike over at virtually zero MPH and CASUALLY completes a 180 degree turn, then reverses himself and does it in the opposite direction several times. I am in awe when I watch him do that as I have NEVER, not once, been able to make a complete 180 there on my own bike (and I've tried MANY times.)
In any event, Bill, I am not arguing that professional braking skills is better than (certainly not more responsive than) ABS. I am saying, however, that well practiced braking skills are fundamentally important to the safety of a rider over time. To become reliant on ABS to make up the difference between proper brake usage and thoughtless brake usage probably is a good thing - when you are driving a bike with ABS. However, as you know, we have all, from time to time, ridden bikes other than our own. What then?
In any event, for those who are reading this thread and are not yet quite sure what this topic is all about ... When your rear brake locks and your rear tire then begins to skid/slide it is NOT true that you have 'lost' all traction. Instead, traction has been significantly reduced. Even while sliding the tire maintains upwards of 80% of the traction it had prior to the skid.
In other words, even with your brake locked and rear wheel skidding you will slow down, just not as quickly as you would if the tire was not skidding.
So, if while ABS is cycling it has 100% braking effectiveness during half of its cycle and near zero during the other half of that cycle, that means an AVERAGE of only 50% braking power. As a skidding tire generates more stopping power than that, why would anyone expect ABS to stop you faster than good braking practices (or even as fast as a skidding tire?)
There are two obvious reasons: the first is that a skilled rider can recognize and stop a rear wheel skid in a matter of a few tenths of a second and, thus, regain full braking power. Unfortunately, most people are not skilled enough to do so quickly (or to recognize that a skid has begun quickly enough) and pretty soon after beginning a skid the rear tire begins to slide (to the side.) Once THAT has happened it is foolish in the extreme to release the rear brake as a highside is quite possible as a result - so, MSF and most other responsible motorcycling organizations argue that once a rear brake is locked you SHOULD LEAVE IT LOCKED. Good advice, but the result is that it will take a relatively long time to come to a stop with only 80% traction. ABS allows VERY FAST return to normal braking with minimum time at only 80%. Even if the effective braking was only 50% while it was cycling, it returns to 100% quickly as compared to manual efforts.
The second reason is a little tricky. If you never locked your rear brake it is a certainty that you have NEVER USED THE MAXIMUM BRAKING POWER YOU HAVE. That is, maximum braking power occurs at the point just before a skid occurs. If you are so concerned about avoiding a skid that you use your brakes too conservatively, you have voluntarily left stopping power on the table. ABS allows you to 'go for it' with confidence and, thus, more likely attain proximate maximum braking power.
As I said, I am coming to believe that ABS makes sense for many people and that the only rationale, (other than cost,) for not having ABS is if you practice and maintain professional level braking skills. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/26/2003 : 9:10 AM
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| (From: drwebb) A late model ABS-equipped BMW riding friend has described an evasive maneuver during which he claims he successfully executed a brake AND swerve. This ability is an established benefit with autos, but does it also apply to MC-ABS? (anyone with an owner's manual?) If ABS allows simultaneous evasive maneuvers, that alone would seem to justify it to my thinking. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/26/2003 : 10:19 AM
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Fascinating concept!
Traction is not determined by brakes - but it IS consumed by their usage. It is also consumed by swerving. In combination you quickly run out of traction. However, if brakes are AUTOMATICALLY backed off as traction becomes less available for braking (as would be the case with ABS) then, I suppose, the odds are better that you could get away with braking and swerving at the same time.
(It would mean that your brakes would be less and less a factor in that escape plan.)
A scary thought, actually. When I use my brakes aggressively I want to stop! When I swerve I want to change directions. Doing both at the same time seems contra-intuitive. I cannot imagine recommending to a student that he consider using both brakes and swerving in a panic, but I know that many want to do so and it's possible that ABS increases the odds of surviving such wrong headed behavior. <G> |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/26/2003 : 3:47 PM
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ABS. Don't leave home without it.
Consider this. It is nearly impossible to high-side an ABS equipped bike because you can't lock up the rear wheel. This is a very good thing and worth the price of admission right there.
Consider this too. It is by definition impossible to practice emergency braking. While we can and should practice hard braking this is not emergency braking. When we are practicing braking we know well ahead of time where and when we are going to put on the binders, we are aware and thoughtful of the activity in advance, and we don't have a bloodstream full of adrenalin. By definition, you cannot practice a panic stop where you do not have time to plan it, you may be puckered to the max, and despite all the controlled braking practice you have done there's a decent chance of grabbing too much front bake and stomping on the back. Thankfully, ABS can be there to maintain traction when you're operating on the unplanned adrenaline of a true emergency rather than the planned awareness of a practice stop.
I don't think the calculation that ABS may be 50% as effective as non-ABS because it is pulsing on and off holds any water. Remember, the ABS system kicks in only when the tire has begun to skid. Its purpose is to get you out of that skid almost instantaneously. As soon as the skidding stops, ABS gets completely out of the way.
This last point leads directly to one of the common mistakes people make when analyzing results of ABS vs. non-ABS tests. Real world tests show that on a good surface a good rider without ABS can out-stop an ABS assisted stop. But this is a meaningless comparison. Why? Because it is a comparison against someone who is overbraking on an ABS bike, hence constantly initiating micro-skids, hence causing the ABS system to pulse. This is no way to stop a bike. A decent rider on an ABS bike never engages the ABS system during controlled stops. You maximally stop an ABS bike the same way you do a non-ABS bike, by using up maximum traction without skidding. Your bike is not going to take longer to stop simply because there is an ABS on board. It will only take longer to stop if you push it into wheel lockup where the ABS kicks in. The non-ABS bike takes longer to stop if pushed into lockup too. Unfortunately, ABS stopping distance tests universally compare an ABS bike in the skid zone to a non-ABS bike that is not made to skid. It's a no brainer which will win every time, but it says nothing about the value of ABS. Or to make this point shorter: ABS and non-ABS bikes stop identically if the tires on both are not made to skid. ABS bikes stop quicker than non-ABS bikes if the tires on both are made to skid (unless the non-ABS bike highsides first ;-).
Here's a link to a pretty good real-world ABS comparison (although it does make the same mistake of comparing skidding ABS bikes to non-skidding non-ABS bikes). One of the big takeaways from this report is the huge advantage of ABS on dodgy surfaces - where it may be needed the most.
http://www.ibmwr.org/prodreview/abstests.html
Cheers... |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/27/2003 : 3:23 PM
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James R, I usually agree with you but not with your statement, “When I use my brakes aggressively I want to stop! When I swerve I want to change directions. Doing both at the same time seems contra-intuitive. I cannot imagine recommending to a student that he consider using both brakes and swerving in a panic,......"
First, I don't recommend doing anything in a panic. I recommend not panicking. That said, there are times that you may not stop in time and your swerving area is being possibly cut off. For example, a Deer jumps into the road at night and freezes. He may stay frozen and you can swerve around or he may move again. There are other such scenarios if that one has faults such as things falling off a truck in front of you in traffic etc. In such a situation swerving might save you and it might not. I would want to swerve and get rid of all the speed that I could so that if I did impact, then it would be at a slower speed. Impact forces square with doubling of speed, so any speed that you can get rid of helps tremendously.
In my scenario, if you went straight you hit for sure and at a higher speed. If you swerve and brake, you may miss you may hit, but if you do hit it will be at a lower impact speed than just swerving with no braking. It seems to me that there are times that call for swerving and braking as a best defense.
By the way, I am impressed with your friend’s turns in your driveway. I can do figure eight’s, scraping the floorboards on both sides constantly on my Vulcan Nomad. I saw a police motor officer practicing in a parking lot once and he taught me tight turns. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/27/2003 : 6:42 PM
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Nomad Dan,
I am at a loss to determine what your point was in your reply. Stopping quickly doesn't mean panic! Are you advocating swerving and braking at the same time?
Concerning my abilities of making sharp turns, I'm not impressed either about what Jim said, however, scraping floorboards on a Vulcan Nomad is even less impressive. What does that take 10° lean? ;)
// OB |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/28/2003 : 8:24 PM
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(From: Stephen Webb) My ABS experience comes from cars (specifically European cars equipped with BOSCH ABS systems), so I don't know how well it transfers to motorcycles.
1. Braking distance with ABS (pedal to the floor) on dry pavement tends to be 10-20% longer than a PROFESSIONAL driver braking without ABS.
(my guess is that ABS actually REDUCES stopping distance for typical drivers. Without ABS you have to be somewhat conservative, or you risk locking up your wheels...ABS can explore the limits, and quickly adjust if wheel lock is sensed (or predicted))
2. My understanding is that ABS (modern Bosch system on a car, at least) does _not_ simply pulse the brakes on and off. I believe it is a much more complicated "control system" that can do more than just turn the brakes on and off (eg it can modulate the pressure).
(for a networking analogy, it works more like TCP's congestion control...not like your heater's thermostat)
3. I have heard abs systems modulating the brakes anywhere from 2 to 30 times per second.
2 times per second. 1993 Ford F150 rear axle ABS.
"At least 11 times per second" 1990 Saab 9000 CD turbo
15 times per second (standard quoted Bosch statistic for early 1990s systems)
Up to 30 times per second (some early '90s Cadillac)
From experience, 2 times per second is a piece of poo. 11 and 15 times per second does pretty well, and I am all about ABS on cars.
4. Standing on the brakes and locking them up works better than ABS on gravel. (4 wheelers, BTW)
(That brings up a question...can motorcycles ride on gravel roads at all?)
5. As pointed out by someone else, ABS means a more predictable, controllable vehicle. You can turn and stop at the same time (cars, anyway).
-Steve
(never driven a bike) |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/28/2003 : 10:16 PM
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The one feature that is on at least some, (if not all), BMW motorcycles is that the ABS can be turned completely off. If you think you can do better based on the conditions, (ie. dry pavement), switch it off and then turn it back on for wet-slick conditions.
Just a thought. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/29/2003 : 10:03 AM
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(From: drwebb) Nomad Dan, your response mirrors my own to JRD's comment- perhaps OB would think I didn't have a point either.
First, the historic term of art "panic stop" has been hashed previously on this board, and all agreed it refers to an emergency braking maneuver rather than an attitude of pandemonium in executing it.
Now JRD has elsewhere pointed out the advantages of scrubbing off as much kinetic energy before an impact, so I expected him to appreciate the potential swerve/brake controllability of ABS. Yet he reminded us of the fundamental that traction spent braking- whether by the rider or the ABS makes no difference- is not available for swerving. So to employ either contermeasure most fully one still has to commit to it exclusively.
I remain curious if the ABS-BMW owner's manuals weigh in on swerving+braking since it's not as clear-cut as might be thought. Hopefully as JRD requested an ABS-equipped MC rider will wander along and tell us about their experience? |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/29/2003 : 11:31 AM
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Thank you for providing that information.
There was a time when there was legislation in the United States mandating that all new vehicles (cars) would have to provide ABS based on the expectation that it would significantly reduce accidents and resulting injury/deaths. That legislation was repealed after it was discovered that the number of accidents as between cars with and without ABS was virtually identical BUT that those vehicles with ABS tended to have FAR MORE single vehicle accidents involving running off the road.
It is speculated that when a car locks its brakes and begins a skid/slide that it continues to move generally in the direction it was going at the time the brakes were locked (i.e., in the direction the road goes.) But for cars with ABS that begin to lock their their brakes the drivers feel that they are in more control and try evasive maneuvers that, because of regained traction, causes them to over-correct and lose control of the direction of travel - thus, off the road.
In any event, there is no longer a law that mandates ABS in the U.S.
Yes, on gravel if you simply lock your brakes in a car you will slow faster than with unlocked brakes. This is because the 'dam' of loose rocks that builds in from of the tires provides more resistance to forward travel than braking over the top of those rocks can provide.
And, yes, motorcycles can handle loose gravel very well, with appropriate speed and smooth changes of direction and throttle and brakes. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/29/2003 : 11:53 AM
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I had hoped that my 'emoticon' (<G>) following my comment about being 'wrong headed' would be seen as a grin and suggest that I meant nothing harsh with the comment.
Survival mandates that if you can use your brakes to avoid an accident, you do so. Only if that is not possible should you consider another alternative (such as swerving or accelerating.) And if there is no alternative that avoids an impact, then scrubbing speed is fundamentally important - i.e., maximal braking.
If braking alone cannot stop an impact accident from happening then swerving, alone, might. If not, a combination swerving and braking is NOT the best of both worlds, it is the worst as you can neither swerve maximally nor brake maximally while trying to do both thus you will impact and you will be traveling faster when you do so than had you simply applied your brakes.
I was reacting to suggesting in a public forum that swerving and braking together might be a reasonable approach to be taken on a motorcycle when confronted by an imminent collision. Those of you who have substantial experience on motorcycles might fully appreciate how risky that is but there are those, like several readers of this thread have admitted to, who have little to no experience on a motorcycle. We must not lead these people into making mistakes here. This forum is dedicated to doing just the opposite. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 09/29/2003 : 2:51 PM
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OB, you stated that, “I am at a loss to determine what your point was in your reply.” That surprised me, it seemed to be very clearly stated. I will make an attempt to be clearer.
James R. said, “When I swerve I want to change directions. Doing both (swerve and brake) at the same time seems contra-intuitive. I stated, “I would want to swerve and get rid of all the speed that I could so that if I did impact, then it would be at a slower speed.” Additionally I stated, “If you swerve and brake, you may miss you may hit, but if you do hit it will be at a lower impact speed than just swerving with no braking.”
At no time did I imply that it is possible to put ALL available traction into swerving and still have anything left for braking. That said, (clear enough I hope) I have never (on a street bike) swerved to the point of using all available traction. I haven’t even come close to a loss of traction in a swerve. Therefore there would be traction available to brake with in addition to swerving.
Neither James nor you need to think, believe or teach that. However James stated that it seemed contra-intuitive. In a style of thinking that is either or/black or white, you can only swerve or brake. I maintain, there is traction available in a swerve that could be used for braking. In my scenario, brake going straight you hit for sure or swerve and you might hit might not, it does not seem contra-intuitive to use some of the left over traction to get rid of speed in case you do hit after a swerve. Using some traction for braking doesn't make it so that you can not swerve.
About the floorboard thing:) it is a skill that is useful and harder than might be imagined even though you can. Do you really think that even one percent of Harley Road King riders can turn as sharp as motor officers on Road Kings? I can and my bike is similar in dimensions and setup. When I see riders on a narrow road with limited visibility (a canyon near my home) doing a three or four point U-turn, I find it useful to be able to make a no stop quick 180 degree turn; rather than be in the middle of a pull forward/back up turn with the possibility of cars coming around the corner. On group rides I’m amazed at all the commotion it cause when someone makes a wrong turn and everyone needs to get turned around. Most people simply can’t turn their bikes around in a small space.
I have posted on this site for a long time and I am not a flamer like some that find this site. I simply, and hopefully respectfully, disagree with the idea that you can only swerve or brake. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 10/04/2003 : 12:55 AM
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Much clearer than your previous post. Thanks. You have heard this analogy before, but, I think it applies here. In theory I agree with you 100%, why not brake while swerving? Makes sense to slow if you can. The problem comes when trying to put this into practice. Swerving is typically a very abrupt change in direction. The more the lean, the more you have to back off on your brakes or you go down. Doesn't seem to me to be extremely practical. MSF says to separate swerving and braking and I agree with them in practice.
Thanks again // OB |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 10/19/2003 : 1:57 PM
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This can go on forever - with clarifications ad nausea. I hope this makes clear *MY* black/white thinking:
If you cannot avoid an accident with maximum braking and you cannot avoid the accident by maximum swerving, then BY DEFINITION any combination of the two means that you CANNOT AVOID THE ACCIDENT and that you will collide moving faster than had you merely used maximum braking. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 11/20/2003 : 3:46 PM
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(From: Badger) Jim,
While my Vulcan does not have anti-lock brakes I recently tried out a BMW r1150r which does. BOTH brakes are antilock and linked front to back but NOT back to front. Thus you can trail the rear if you want without engaging the front....e.g. on slow slippery surfaces.....
I tried a panic stop from about 80 mph on a deserted, well paved, four lane highway.....after a brief delay, the bike stopped really really fast. The BMW system is also power assisted.....
I haven't had enough experience with the system to decide if I like it, tho it felt good......but there is probably merit in a system which prevents either wheel from locking up in a panic/emergency situation. I know you emphasize rear lock up as an evil, and I agree, but you can stay upright with rear lock up as long as it stays locked up. Front lock up and down you go.
Oh..those BMW brakes don't work when the engine is off....which makes start up maneuvering interesting. |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 11/20/2003 : 3:55 PM
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| (From: Badger) what about that once in a thousand suddenly slippery surface, anti-freeze, oil on the road, sheet of ice, where a good antilock system saves your life? |
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Badger
New Member
21 Posts
rockville, md
USA
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Posted - 02/11/2004 : 12:59 PM
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Again, an imported thread that though it does talk about ABS, has an interesting side-bar that may be of interest: can you (or should you) brake and swerve at the same time believing that ABS equipped bikes make it less dangerous to do so.
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