"ABS" has been misnamed from day one

[greenwald]

Whoa partner! I appreciate the accolades, but I ain't no Einstein by a long shot!!

I'm just wired like your typical engineer type, that likes to think things out to the n'th degree. However, I do have some strongly formed opnions about how cycles function in the realms of physics and logic, and I try fully understand the dynamics of bikes rather than rely on comments like "ABS will save my butt." Perhaps if I had a cool physics teacher back in high school that rode a cycle and could equate physics to it and me, I woulda aced physics and science easily. Got by ok on a B, but I could have done much better.

Reminds me of Einstein's humility, when while being goaded by a reporter as to how it feels to be the world's smartest human, he simply replied "Son, we're all ignorant...............just about different things."

 

[MOTOR31]

Equipment can only do so much to make up for the lack of rider skills. If a rider requires the same "stability" from their motorcycle that they get from a cage they do not belong on a motorcycle. Neither vehicle requires the same set of skills from the operator and neither vehicle will respond to inputs in the same manner.

As to the semantics of "anti lock brake system" vs "stability system" it's a bit of a misconception that brakes that do not lock on severe application do NOT provide additional stability over a non ABS equipped vehicle. Hence the term stability assistance still applies.

 

[barryg]

I apologise for the inapropiate ABS comment. I was just adding a little humour to the serious discussion of the workings of the abs braking system.

 

[ANDYVH]

Oh, I dunno,....I thought it was totally appropriate. No apology needed.

I'm a Monty Python kind of guy, when the seriousness gets too much, its time for irreverant humor. Humor is good because quite often it exposes the true feelings.

Sure, many may not agree with ABS as a braking or stability system, my intent is to get riders to think beyond either system covering for a rider's mistakes, or worse, a rider's lack of skills. No matter the system or technology, it ALWAYS comes back to the rider. The rider always has to have the skill sets to ride. If a rider does not want to develop those skills, then I have to say that person should not be riding, stick to cars then.

 

[AKsuited]

Perhaps if I had a cool physics teacher back in high school that rode a cycle and could equate physics to it and me, I woulda aced physics and science easily.

I did have a cool physics teacher in high school, Mr. Walters. I don't think he rode a motorcycle.

But this reminds me of something important I did learn in school, that the static coefficient of friction is usually higher than the sliding coefficient of friction. I still remember the example: push on a heavily loaded cardboard box. You will push harder and harder until it breaks loose and slides. The force required to slide it is less than the force you exerted just before it broke loose. The coefficient of sliding friction is lower.

This is why drag racers lose when they smoke their tires. They can't win a drag race using sliding coefficient of friction because it is lower.

So many people fail to understand that. To stop in the shortest distance, you must use static coefficient of friction, not sliding coefficient. Same thing with measuring skid marks at an accident scene: somewhat informative in the sense that brakes were applied, but is misses the point: the driver would have stopped shorter by not leaving skid marks. And this is where ABS comes in: it keeps you in static coefficient of friction territory and avoids sliding coefficient of friction.

Back to leaned over bikes: you need an ABS system between your ears that knows that motorcycle tires have a limited amount of static friction available and that most of it is used up being leaned over. Jacking your brakes will quickly overwhelm that limit, put you in sliding coefficient of friction territory, and at a minimum have your rear wheel step out or worse case, have you go down hard. Since the forces used to get you around the curve are sideways, the ABS system on the bike can't possibly know about them, and can't help you avoid sliding out.

Harry

 

[Anyname]

This is why drag racers lose when they smoke their tires. They can't win a drag race using sliding coefficient of friction because it is lower.

Hmmm, most dragsters light them up for quite some distance. It may be that they are just using their tires and the road surface to augment their clutches, but they definitely spin their wheels.

I have had people knowledgeable in physics explain tire to road traction in terms of basic physics, and it always seems to imply that traction is determined by the load on the wheel. Also that the surface area of the tire on the road isn't important. Based on actual observations of vehicles, I have to conclude that the basic physics are only part of the equation, and that rubber compounds, tire construction, tire geometry (tall and narrow vs low and wide), temperature, the road surface (both large and small irregularities), vehicle suspension and a host of other things have a large effect on traction as you experience it on a vehicle.

 

[ANDYVH]

Yeah, I agree. Tire traction is a black art in itself, many more variables than just tire load and surface are of contact.

I also understand the reply about static and sliding friction, and I think I understand your point. Though I can't quite agree on the aspect of static versus sliding friction. Static friction has much to do with the "breakaway force" to get a stationary body in motion. Consider a heavy metal block on a table top. It takes more force to get it moving, than it does to keep it moving.

Since a motorcycle in motion is the main realm of ABS system, it is more sliding motion even if the tire does stop rotating. The mass of bike and rider in motion, in contact at the road on the tire contact patches, I think is still sliding friction versus static friction. Most ABS systems require a 10% to 20% slip thresehold to be exceeded for ABS control to engage, which is the tire already sliding slightly while the bike is in motion.

Interesting discussion though, far deeper than reviewing what latest piece of shiny chrome bling some riders focus their discussions on. Chrome don't get you home!

 

[AKsuited]

Since a motorcycle in motion is the main realm of ABS system, it is more sliding motion even if the tire does stop rotating.

As soon as the tire stops rotating, it is all sliding motion, and sliding coefficient of friction. That's basically all an ABS system does: check to see if the wheel is still rotating. If it isn't, then by definition the tire is sliding.

The mass of bike and rider in motion, in contact at the road on the tire contact patches, I think is still sliding friction versus static friction.

I have to disagree. As long as the tire is not sliding, it is static coefficient of friction.

Most ABS systems require a 10% to 20% slip thresehold to be exceeded for ABS control to engage, which is the tire already sliding slightly while the bike is in motion.

I don't know enough about the details of ABS systems other than to point out as above that the whole purpose of ABS is to detect a non-rotating wheel, and cutting off braking force to the wheels when that happens.

Harry

 

[ROLLIFAHRER]

It seems much of the thread relates to hard braking in corners. I think we'e asking too much of mechanical systems when we expect them to defy certain laws of physics.


In my limited experience, I've discovered that ABS does a good job of preventing wheels from locking up while braking hard IN A STRAIGHT LINE.

In all of my reading and training, most braking should occur before entering a corner, while the bike is vertical and traveling IN A STRAIGHT LINE.

If one misjudges entry speed and needs to apply more brake force prior to the turn in point, ABS intervenes in the event the rider panics and applies to much force to the lever and/or is not skilled at predicting maximum braking without locking up.

Used as intended ABS in fact does prevent wheels from locking, and the OP's claim that a wheel must lock in order to enable ABS functions is not correct. The control unit reads sensor data at a rate of 4 - 8 milliseconds and pulses the valves at 16 times per second. The control unit measures wheel speed and engages when a wheel BEGINS to slow, but before it locks--hence Anti Lock Braking.

The following uses automotive 4-wheel ABS as an example, but the principles apply to all ABS.

Use (Wiki)

There are many different variations and control algorithms for use in an ABS. One of the simpler systems works as follows:[15]
The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 km/h) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation the driver will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. This pulsing also tells the driver that the ABS has been triggered. Some ABS systems can cycle up to 16 times per second.

 

[ANDYVH]

Used as intended ABS in fact does prevent wheels from locking, and the OP's claim that a wheel must lock in order to enable ABS functions is not correct.
I am not saying the wheel must "lock", but I am saying the wheel MUST exceed a slower speed preset thresehold before ABS control engages. In many cases, that means the braked tire IS slightly slipping, not locked. BUT! The point is I don't want to rely on a slightly slipping tire which is exceeding traction limits.

The control unit reads sensor data at a rate of 4 - 8 milliseconds and pulses the valves at 16 times per second. The control unit measures wheel speed and engages when a wheel BEGINS to slow, but before it locks--hence Anti Lock Braking.
True, I am not argueing that point. It engages control BEFORE the wheel locks but AFTER the braked wheel IS spinning slower than the other wheel and the actual vehicle speed. It is at THAT point, if leaned over, that I believe ABS stability cannot be fully relied upon. If you are already near the traction limit, then ABS slightly exceeds the traction limit as control is engaged.

I have said it before, and I have not yet read or found anything to disprove it: that ABS systems function on the preset condition of a wheel, with braking applied, slipping at a rotational speed up to 20% less than the actual vehicle speed.

I would really like to find out the actual control parameters typical of motorcycle ABS systems to be disproved on this. But really, my intent on this post is to get riders thinking beyond the realm of "ABS will save my butt if I mess up, even if I do it in a corner." Not true, to me, until proven otherwise.

 

[BCKRider]

A few (probably ignorant) questions about ABS

1. Isn't the MAIN PROBLEM with both car and bike ABS the fact that so few users "test it" until faced with a real event? When I got my first car with ABS in 1991, I made myself try slamming on the brakes on snowy roads, starting very slowly and always making sure there were no following vehicles. The impulse, ingrained from years of driving cars which lacked this feature, of releasing the brake when you heard and felt the ABS activating was VERY STRONG. I still do this drill every year after the first snowfall - and I know I am negligent for not practicing the same thing in the rain. And maybe also on dry pavement.

I only once got to "practice" steering with the ABS activated - and am still amazed that I remembered this piece of information when I really needed it. But I steered my way around a couple of stalled vehicles while descending a very slippery road. Would have had a fender bender, without question, without ABS.

I wish I had conducted the same tests on my current bike - when the ABS actually worked. Well, I sort of did with the rear brake on gravel. Seems to me the rear brake produced a number of "mini-skids." (BMW ABS-1.) Anyone who has dumped their bike because of locking the front wheel probably tends to be leary of trying "threshold braking" to the point of getting to "where the front end seems rubbery" or whatever other descriptive the pro's use for the point just before a crash. But ABS would be absolutely the best way of safely experiencing maximum braking. At least when the bike is upright.

2. How have BMW bike ABS systems improved since the first one? (I would hope improved reliability, but other than that?)

3. With modern bike ABS systems, is the old idea of "a quick squeeze" rather than a "sudden grab" still appropriate? (Still talking about a straight ahead stop.)

4. "Stopping in a curve," or even braking, still seems to be the topic which generates the least consensus among the "experts." Seems on this thread there is disagreement about whether the newest systems do any good at all, though maybe consensus that you can't hit the brakes when leaned well over on a wet curve with a bunch of gravel and expect all will be well. My approach (which many of you will think ridiculously conservative) is to slow down and gear down before the curve to a speed which allows me to do some engine braking while reaching for the brake lever and righting the bike in a worst case scenario.

Always more to learn.

 

[ANDYVH]

1. Isn't the MAIN PROBLEM with both car and bike ABS the fact that so few users "test it" until faced with a real event?
EXACTLY! I have always said any rider on any bike HAS to practice basic high effort braking skills, regularly. Same for ABS equipped bikes. Practice stops until you develop a "feel" for what you and the bike can/cannot do.

ABS on gravel is hampered by the "damming" effect of gravel piling up in front of the tire. Then, even though the ABS releases brake pressure, the lag time of the tire plowing through the gravel "dam" does indeed produce mini-skids. If it happens enough, the mini-skids can cause the ABS to go into fault mode and shut off. That's why many off-road ABS systems have an ON/OFF function.
2. How have BMW bike ABS systems improved since the first one? (I would hope improved reliability, but other than that?)
Biggest improvements are reduced weight, smaller components, higher "cycle rates" of braking pulses, and much higher computing capabilities.
3. With modern bike ABS systems, is the old idea of "a quick squeeze" rather than a "sudden grab" still appropriate? (Still talking about a straight ahead stop.)
Proper basic braking technique ALWAYS has priority, so it is better to still use the skills you know, and hopefully practice, that being the quick, progressive, increasing squeeze. If you just "grab" and either never achieve the full braking thresehold, of always exceed it, you'll never develop proper braking "feel" and you'll be over-reliant on ABS saving your butt and not knowing what you did to cause it.
4. "Stopping in a curve," or even braking, still seems to be the topic which generates the least consensus among the "experts." My approach (which many of you will think ridiculously conservative) is to slow down and gear down before the curve to a speed which allows me to do some engine braking while reaching for the brake lever and righting the bike in a worst case scenario.
Actually, I agree with your technique entirely, and use it almost all the time. Using this technique does not also make you a slow pace rider. Smooth, consistent traction and minimal chassis pitching are part of my riding style, and I tend to be somewhat quicker through the turns actually. I also do not depend or expect ABS to do anything for me when I am already leaned into a turn. Again, back to good basics. Scan/search BEFORE the turn, setup BEFORE the turn, slow-in/roll-up (throttle) through the turn, look to the exit. Doing this helps to mininmize reliance on any system other than the best one, between your ears, which is the only true Motorcycle Stability system.

 

[ANDYVH]

In the past I had discussed ABS systems on cycles with David Hough and Ken Condon. We pretty much all agreed that ABS can really only be relied upon for braking and stability when the bike is vertical or as near vertical as possible.

I recently emailed back and forth with Keith Code on this same subject. After about three rounds of emails I got this back from Keith, "For sure, the best advice for anyone is to get the bike as vertical as possible for any braking maneuver, ABS or not, especially on the road."

 

[globalrider]

ABS-less by choice, even if it were FREE.

 

[globalrider]

In the past I had discussed ABS systems on cycles with David Hough and Ken Condon. We pretty much all agreed that ABS can really only be relied upon for braking and stability when the bike is vertical or as near vertical as possible.

Been posting that on forums well over ten years ago, long before I even heard of those two.

Its basic physics...not rocket science!

 

[ANDYVH]

True, I agree. It aint rocker science for sure.

But I bet a lot of cycle riders, even those who did well in High School or College physics classes still think ABS will help them when leaned over in a turn.

 

[globalrider]

True, I agree. It aint rocker science for sure.

But I bet a lot of cycle riders, even those who did well in High School or College physics classes still think ABS will help them when leaned over in a turn.

Have them look up "traction circle".

 

[ANDYVH]

Yeah, I live the "traction circle" as a MSF instructor of 20 years. But actually, living in the traction circle really brings a lot of riding into perspective as far as what you can expect, and what you can do.