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galileo
Ex-Member
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 Posted - 09/21/2009 : 8:26 AM
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There are several aspects to braking:
1. Perception of a hazard
2. Reaction to the hazard
3. Applying the brakes properly
4. Stopping.
I do consider the first two to be the most important as they can eliminate the need for threshold braking. But should threshold braking become necessary, it's critical that it be done right.
There are some mistakes I've observed:
1. Using too much rear brake which results in a skid.
2. Using too little front brake which results in a longer stopping distance.
3. Applying the front brake too slowly which increases stopping distance.
4. Applying too much front brake before the load transfer is complete which can result in a front wheel skid.
5. Applying too much front brake.
Rather then writing a book in one post, I'll address just the issue of using too much rear brake. How much rear brake is needed is a function of the height of the CG and how far forward the CG is. Some bikes do well with little or no rear brake. Others get 30% of the braking force from the rear brake. One can determine a value pretty closely just by intuitively looking at their bike. No need to measure with a micrometer. If the CG is low and aft, more rear brake will be needed. If it is high and forward, less rear brake will be needed. The pressure ranges from almost none to just a light pressure. Some bikes like the Buell have the rear brake dumbed down, so more pressure might be needed to get light braking.
In order to internalize the pressure needed, one can practice stopping using just the rear brake. Pick a pressure which results in stopping in about 66 feet for bikes with a low aft CG and further with a high forward cg. The idea is to ingrain a pressure into the mind where this becomes automatic. Then add front brake while using the same amount of rear brake and gradually decrease the stopping distance. If a rear wheel skid occurs, then go back to the rear brake practice using less rear brake until the new pressure is internalized. Experienced riders can walk the distance in pretty quickly.
Personally, I use the same rear brake pressure for every stop on the road. There is no danger of a skid at less than threshold braking as not enough load has transferred for this to occur. Then I modulate the stopping distance with the front brake. Then for a threshold braking situation, I'm only focusing on the front brake as the rear has become automatic. Using this technique, every stop becomes a partial threshold braking exercise.
The hazard that exists is if a person gets in the habit of using too much rear brake for less than threshold braking, there is no punishment. The punishment will only occur in a threshold braking situation when there is more load transfer and a rear wheel skid occurs.
A g-meter with an instantaneous readout can be had for about $42. One with data recording is about $87. The advantage to a readout is a rider knows exactly what's happening during practice and can adjust their technique accordingly. Personally, I have the first and have ordered the second. There are many other aspects of riding that can be easily analyzed with a data recorder.
I guess it's kind of like wearing a helmet. We each draw our own lines of safety. If some want to "just go practice braking" that's what they will do. The result will vary. If some want to make a science of it, then they may be safer as a result. Maybe those who want to approach things scientifically can come up with a learning process that can be used by those who prefer a non-scientific approach.
As for BRC, I realize time is limited and stuffing more into a new rider's brain just isn't possible. I think the problem could be resolved simply with a section in the book on how to practice braking on your new bike.
The purpose of this thread will be to come up with a practice technique that is effective and short enough so that people will actually do it.
Added the words "too much" with front braking
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Edited by - galileo on 09/21/2009 10:41 AM |
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whittlebeast
 Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/21/2009 : 2:42 PM
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quote:
Originally posted by galileo
.....
Personally, I use the same rear brake pressure for every stop on the road. There is no danger of a skid at less than threshold braking as not enough load has transferred for this to occur. Then I modulate the stopping distance with the front brake. Then for a threshold braking situation, I'm only focusing on the front brake as the rear has become automatic. Using this technique, every stop becomes a partial threshold braking exercise.....
When I first started riding I found the logic involved in using two separate controls to stop a little difficult to get my head around.
I wound up writing a computer program to bring the majority of this into focus.
Statements like yours quoted above will jump out at you once the programming is done. Like most things that you start out to understand get messy at first but later some very odd things turn out to not make any difference. Other things wind up making far more difference than you even dreamed.
WB |
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scottrnelson
Advanced Member
5258 Posts
[Mentor]
Pleasanton, CA
USA
KTM
990 Adv, ST2, XR650L
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Posted - 09/21/2009 : 3:01 PM
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quote:
Originally posted by whittlebeast
I wound up writing a computer program to bring the majority of this into focus.
As a computer scientist, I'm rather curious as to what you would put into a program to deal with braking on a motorcycle. |
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galileo
Ex-Member
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Posted - 09/21/2009 : 3:06 PM
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quote:
Originally posted by whittlebeast
quote:
Originally posted by galileo
.....
Personally, I use the same rear brake pressure for every stop on the road. There is no danger of a skid at less than threshold braking as not enough load has transferred for this to occur. Then I modulate the stopping distance with the front brake. Then for a threshold braking situation, I'm only focusing on the front brake as the rear has become automatic. Using this technique, every stop becomes a partial threshold braking exercise.....
When I first started riding I found the logic involved in using two separate controls to stop a little difficult to get my head around.
I wound up writing a computer program to bring the majority of this into focus.
Statements like yours quoted above will jump out at you once the programming is done. Like most things that you start out to understand get messy at first but later some very odd things turn out to not make any difference. Other things wind up making far more difference than you even dreamed.
WB
I'm not sure if you are agreeing with me or disagreeing, but either way I'm happy. |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
Peer Review:
1
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Posted - 09/21/2009 : 3:27 PM
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quote:
Originally posted by scottrnelson
quote:
Originally posted by whittlebeast
I wound up writing a computer program to bring the majority of this into focus.
As a computer scientist, I'm rather curious as to what you would put into a program to deal with braking on a motorcycle.
[In a fit of pique whittlebeast deleted the link he posted to his spread sheet. It turns out that the next message captured the link and can be used, if you want, but it appears that whittlebeast would rather you didn't have access to it. Pity, since it is an excellent spreadsheet. If he doesn't want you to have access to that spreadsheet, he merely has to ask me to remove the reference from the next message and I'll happily oblige him. JRD]
Here you go. The default numbers in that sheet are off my Sporty. I never bothered to model the FZ1. Most of what I have been messing with on it are on the HP and aero side of the equation.
WB |
Edited by - whittlebeast on 09/26/2009 2:58 PM |
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scottrnelson
Advanced Member
5258 Posts
[Mentor]
Pleasanton, CA
USA
KTM
990 Adv, ST2, XR650L
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Posted - 09/21/2009 : 3:52 PM
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quote:
Originally posted by whittlebeast
Here you go. The default numbers in that sheet are off my Sporty. I never bothered to model the FZ1. Most of what I have been messing with on it are on the HP and aero side of the equation.
http://www.ncs-stl.com/motorcycle/brakeCalcs10.xls
That's impressive.
I wouldn't call it a "computer program", though, since it's actually an Excel Spreadsheet. For your uses, a spreadsheet is much quicker to generate than an actual computer program. |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/21/2009 : 4:01 PM
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Excel is really an old Basic Programming language With variables in a row by column naming convention.
Glad you like it.
The most interesting thing that I found in doing that is that the rear breaking pressure is essentially a constant (and a very small one at that) no matter the situation. Who would of thunk it...?
WB |
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Andrew Dressel
Standard Member
153 Posts
Milwaukee, WI
USA
Moto Guzzi
California Special
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Posted - 09/22/2009 : 9:22 AM
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quote:
Originally posted by whittlebeast
Here you go. The default numbers in that sheet are off my Sporty. I never bothered to model the FZ1. Most of what I have been messing with on it are on the HP and aero side of the equation.
http://www.ncs-stl.com/motorcycle/brakeCalcs10.xls
WB
First, in case what I write below comes across as critical, let me state up front that I find your spreadsheet very slick, though I doubt you need to hear it from me. Thanks for posting it.
Second, I agree with Scott and find your assertion that "Excel is really an old Basic Programming language" a little odd, but would be fascinated to learn more about that, though we probably should take that off line.
Third, you obviously know what you mean by 'total mass', but for public consumption you might do better with 'total weight'. See, that right there sounds snotty, but I don't know how to mention a trivial issue in a way that doesn't.
Anyway, I am happy to report, in case anyone was skeptical (was I the only one?) that the equations embodied in the spreadsheet calculate load transfer in a way that matches the equations Cossalter provides (page 97 of Motorcycle Dynamics).
If I understand your spreadsheet correctly, it goes like this, though I might have some steps out of order. Here I use Cossalter's convention of measuring from rear hub and his symbols: p = wheelbase, b = horizontal distance to static cm from rear hub, h = height of cm. Of course g = acceleration of gravity, m = mass, w = weight, and a = acceleration/deceleration:
1. Calculate brake force (from all the brake parameters specified): F
2. Verify that brake force does not exceed available tire friction
3. Calculate 'geez' of deceleration: geez = a/g = F/w
4. Calculate 'dynamics cm location': d = (p-b) - (a/g)*h
5: Calculate rear wheel load after load transfer: Nr = w*(d/p) = w*(p-b)/p - w*(a/g)*h/p
Replacing w with m*g, canceling the gs in the last term, and replacing m*a with F yields Cossalter's formulation: Nr = m*g*(p-b)/p - F*h/p
Since edited to improve grammar. |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/22/2009 : 10:02 AM
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I really don't remember the order that I did the math as that was a few years ago. It has been some time since I have caught it in error. I tend to program like an engineer and not like a "programmer". I look at what I know, what I think I know, and then can I solve for the next thing that I think I need. Once I get the answer I think I am looking for, then I look for ways to verify the answer I got under a situation that I know the right answer. I was not looking at any book or other referenced source when I did that so....
That was done as a learning experience but some of the finding in that sheet will be worked back into my next racecar. I ran the findings past a good friend that is a head engineer for a stock car race team (came from Indy car racing) and he laughed and then said "yep we found that also when we had a cheater ABS system hid in the car. Never could find a good way to hide the hardware well and gave up."
Glad you like it.
You ought to see the spreadsheet I have for winged 4 wheel stuff. I have way too many hours in that one to post it publicly.
WB
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Edited by - whittlebeast on 09/22/2009 10:13 AM |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/23/2009 : 1:39 PM
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There are a very few possible conditions as you got to evaluate the braking capability of a motorcycle.
When only using the front brake
1) The bike does not have the ability to lock the front tire
2) The bike has the ability to lock the front tire, and right before this happens the bike is not stopping at the max decel as dictated by the CofF
3) The bike can stop at very close to the max decel as dictated by the CofF and the rear tire remains on the ground
4) The bike is capable of doing a Stoppie and does so before the front tire skids
If a person is unwilling to test their bike to find what their bike does at the limit and they are not willing to use my program (that I posted above) to predict what will happen when they ever do get into the situation, then they are setting themselves up for a very bad day sometime in the future.
Having the talent of driving at the limits when the situation must be practiced before you are in the situation.
Note that none of this testing on the bike is for the faint of heart but neither is crashing. I personally elect to do the math route first and then test.
WB |
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James R. Davis
Administrator
14930 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 09/23/2009 : 2:02 PM
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quote:
Having the talent of driving at the limits when the situation must be practiced before you are in the situation.
Despite what you say, in my opinion it NEVER makes sense to drive at or even near limits.
For example, if you want to learn how to threshold brake it is NOT necessary to EVER make an emergency stop from a speed greater than 30 mph. To invite or suggest that civilians (NOT competitive racers) practice emergency braking at highway speeds, or to practice stoppies or wheelies, or ANYTHING that approaches the limit of the bike is totally irresponsible.
A rider's limits may not be anywhere near the limits of his bike, and improving one's skills always involves putting one's toes over the line. But trying to approach a bike's limits is foolish and DANGEROUS.
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/23/2009 : 4:07 PM
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I just can't accept the logic.
1) if you are careful, then you will never get into a 70 MPH full load brake test
2) if number one is true there is no need to practice that situation as it will never come up.
Twenty or thirty MPH may be a good place to start practicing but eventually the rider must be able to execute this from any speed that they ride. Whatever that speed may be.
If the schools have been forced into this view based on liability reasons, then the riders will be forced to learn this on there own one way or the other.
I elect to teach my family to stop. You never know when they will thank you for the effort. If they scratch the tupperware learning, so be it. For the record, my family always ware CE rated slide suits and Snell rated headware. A few thing I leave up to the pros to do the testing for me.
My children have called me on several occasions over the years and said with a broken voice "Dad?... Thanks for taking me to racing school. It just saved my butt."
WB |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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twc
Advanced Member
659 Posts
[Mentor]
Fort Collins, CO
USA
Harley-Davidson
Electra Glide Ultra
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Posted - 09/24/2009 : 10:43 AM
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quote:
Originally posted by whittlebeast
This is the sort of thing that happens when the rider does not understand the capabilities and limits of both himself and his bike.
WB,
I am willing to concede that you may have a point about braking practice, but the video you have chosen appears to illustrate more fundamental problems than a thorough understanding of braking capabilities and limits. I'd choose again. 
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galileo
Ex-Member
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Posted - 09/24/2009 : 10:55 AM
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quote:
Originally posted by twc
quote:
Originally posted by whittlebeast
This is the sort of thing that happens when the rider does not understand the capabilities and limits of both himself and his bike.
WB,
I am willing to concede that you may have a point about braking practice, but the video you have chosen appears to illustrate more fundamental problems than a thorough understanding of braking capabilities and limits. I'd choose again.
This video is generally a good ride:
http://www.youtube.com/watch?v=KO2z...78A1&index=1
But there may be some things the rider may not know about the capabilities of himself and the bike. See if you can pick them out.
Edited to separate quote from my post. |
Edited by - galileo on 09/24/2009 11:32 AM |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/24/2009 : 11:24 AM
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In the video I posted, the guys HUGE mistake was underestimating the power of the bike followed by a total lack braking talent. Granted, it was a little over the top but it gets the point across. You have to know your bike and learn it in a controlled and gradual way.
Can we get to the procedure of learning braking now? This is the part that you just can not learn from just reading a book, but a book can sure help you thru the learning curve.
WB |
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scottrnelson
Advanced Member
5258 Posts
[Mentor]
Pleasanton, CA
USA
KTM
990 Adv, ST2, XR650L
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Posted - 09/24/2009 : 11:35 AM
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quote:
Originally posted by galileo
This video is generally a good ride:
http://www.youtube.com/watch?v=KO2z...78A1&index=1
But there may be some things the rider may not know about the capabilities of himself and the bike. See if you can pick them out.
I am unable to understand the point of that video. I didn't see any braking in it (this is a thread about braking, right?). And the road didn't seem to require any exceptional skill to ride.
Would you mind explaining what we were supposed to see in that? |
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galileo
Ex-Member
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Posted - 09/24/2009 : 2:19 PM
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quote:
Originally posted by scottrnelson
quote:
Originally posted by galileo
This video is generally a good ride:
http://www.youtube.com/watch?v=KO2z...78A1&index=1
But there may be some things the rider may not know about the capabilities of himself and the bike. See if you can pick them out.
I am unable to understand the point of that video. I didn't see any braking in it (this is a thread about braking, right?). And the road didn't seem to require any exceptional skill to ride.
Would you mind explaining what we were supposed to see in that?
Thanks for asking, Scott. Perhaps I mixed topics with the one on minimum braking. But I was piggybacking on whittlebeast's "know the capabilities of your bike" as well as the data from the study I posted.
The key to threshold braking successfully is don't do it. In the middle part of the video, the rider was pressing the 2 second following distance. With one car ahead of him, it might not be so bad, but the two cars ahead of that car were disappearing around the curve. They may have set up a stopping wave that would have resulted in hard braking. The other thing is that the rider was at times was riding between the tire tracks with less than two second spacing. This would have made the time to react very short had the vehicle ahead straddled a rock or a muffler or something.
To address the capabilities of the bike more directly, if the vehicle ahead braked hard in a curve, the rider may not have been able to stop unless they realized how much braking a bike can do in a curve. The only real way to know this is to try it in a series of gradual tests to see if any handling issues come up. On one of my bikes it really doesn't like me to use any front brake in a curve as the front wheel starts to wobble and there is a real tendency to go wide. It is controllable, just startling the first time.
Sorry, I realize this might be perceived as a trick question. I probably should have put it in a thread from way back that has situations and a challenge to see if one can catch the errors.
Some may disagree with my analysis, and that's ok, as long as it makes us think. |
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whittlebeast
Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/24/2009 : 2:36 PM
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quote:
Originally posted by galileo... On one of my bikes it really doesn't like me to use any front brake in a curve as the front wheel starts to wobble and there is a real tendency to go wide. It is controllable, just startling the first time....
A great example of the sort of thing that comes up in testing.
WB |
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scottrnelson
Advanced Member
5258 Posts
[Mentor]
Pleasanton, CA
USA
KTM
990 Adv, ST2, XR650L
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Posted - 09/24/2009 : 3:30 PM
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quote:
Originally posted by galileo
Some may disagree with my analysis, and that's ok, as long as it makes us think.
I appreciate your explanation. That makes it much more clear and points out a few things that I didn't really notice. |
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galileo
Ex-Member
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