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 'Grabbing a handful' - what does that mean?
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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/21/2010 :  2:22 PM Follow poster on Twitter  Join poster on Facebook as Friend                        Like
We have in another thread on this site recently discussed braking performance and, in particular, we looked at a large set of braking skill test runs done by the Idaho STAR administrator, 'Ax' Axmaker.

Those runs were performed at three different speeds: 20, 25 and 30 mph.

I have challenged the results of those tests because far too many of them showed braking performance well beyond the capabilities of even competent riders, and some of them were beyond the capabilities of most motorcycles.

It is my contention that unless a person can consistently achieve a deceleration rate of at least 0.7g's, that person is not 'qualified' to ride a motorcycle on public roads, and that if the rider can consistently achieve deceleration rates of at least 0.8g's, he or she is a competent rider in terms of braking skills.

The test results, however, showed that a group of highly skilled riders consistently achieved deceleration rates well in excess of 1.0g's, with several achieving 1.1g's and a few even achieving a deceleration rate in excess of 1.2g's.

I'm not going to argue why those rates that are in excess of 1.1g's are highly suspicious here (but you will understand why when I finish this message.) Instead, I want to explore the concept of 'rapidly squeezing' the front brake lever.

We all know that 'grabbing a handful' of front brake lever is dangerous. That is, squeezing the front brake lever too quickly leads to locking up the front brake and the result is a bike that ends up on its side - almost faster than you can blink.

But how fast is too fast?

Well, I'm betting that you've heard otherwise knowledgeable riders and even instructors suggest that you should squeeze hard, then squeeze harder, then harder still until you've achieved your maximum deceleration rate. And when asked how long it should take until you've reached that maximum, you hear suggestions such as 'about one second'. NUTS!!!

It should never take you as long as .7 seconds to reach maximum squeeze pressure on your front brake lever when you are trying to stop aggressively. In fact, most people can easily hit their maximum squeeze pressure in .5 seconds, and with practice you should be able to reach maximum in about .3 seconds. That's a HUGE difference in reality and the well intentioned suggestion of 'about one second'.

On the test range you are to attain a given speed and then stop as quickly as you can. For example, you are to begin braking at 20 mph and you should come to a complete stop within seventeen feet in order to achieve a deceleration rate of 0.8g's.

The deceleration rate is the average deceleration rate during that stop. But in actuality, until you reach your maximum deceleration rate (maximum squeeze pressure), your deceleration rate is obviously less than 0.8g's, if the average is 0.8g's. Which means, of course, that the maximum achieved deceleration rate is higher than 0.8g's.

Let's look at what happens to the deceleration rate when stopping from a speed of 20 mph if it takes you only 0.3 seconds to reach your maximum squeeze pressure.



If you average a deceleration rate of 0.8g's, you will come to a complete stop in 1.1 seconds (and take 16.7 feet). The chart above shows that for the last 0.8 seconds you must have achieved a deceleration rate of 0.93g's, because for the first 0.3 seconds you had to have averaged half of that rate.

That is,
.8X + (.3 *.5)X = 1.1 * 0.8
.8X + .15X = 0.88
.95X = 0.88
X = 0.93

In other words, to achieve an average deceleration rate of 0.8g's when stopping from 20 mph and using 0.3 seconds to reach your maximum deceleration rate, that maximum had to be 0.93g's.

Bravo! You now know that a competent rider in terms of braking skills actually achieves a rate in excess of 0.9g's in order to average 0.8g's when stopping from 20 mph.

But this thread is about how long it takes you to achieve your maximum deceleration rate, not what the maximum rate is. Still, it's very informative to explore what happens if you take longer than 0.3 seconds to reach your maximum. What, for example, happens to deceleration rates if it takes you as much as 0.7 seconds to reach your maximum?




If it takes you as long as 0.7 seconds to reach your maximum squeeze pressure, you must achieve a deceleration rate of 1.17g's when you get there in order to average 0.8g's. I showed that in red in the chart above because that deceleration rate is extremely near skidding even on good concrete, let alone asphalt. It should be no surprise that if an instructor suggests that it takes you 'about one second' to reach your maximum squeeze pressure, he doesn't really understand the real world.

But what this little example clearly shows is that it is much easier to achieve a deceleration rate of 0.8g's when stopping from a speed of 30 mph than it is if you are stopping from 20 mph. (It takes 1.7 seconds to come to a complete stop from 30 mph if you average a deceleration rate of 0.8g's.)





And so I suggest that 'grabbing a handful', when meant as a pejorative indicating dangerous behavior, also means taking less than 0.3 seconds to reach maximum squeeze pressure.

I also suggest that when you do parking lot practice braking runs you pay more attention to getting to maximum deceleration rate quickly than you do at the distance it takes you to stop.

You will need the following chart to determine your deceleration rate:

aidanspa
Male Advanced Member
1739 Posts
[Mentor]


Omaha, NE
USA

Harley-Davidson

Road King

Posted - 11/23/2010 :  2:39 PM
I have read this post several times and am fascinated by the mind behind it. Great stuff.

Jim, in focusing our attention on the time it takes to get to maximum deceleration rate during PLP, particularly for newbies, is there a better way to determine what that may be than the distance it takes us to stop from a given speed?

Thanks for the thread.

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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/23/2010 :  3:10 PM Follow poster on Twitter  Join poster on Facebook as Friend  
Jerry, [oops, Robert]

The only practical way to determine how quickly a newbie can stop is by using speed and distance. The distance marks are static on the ground while the instructor measures both time through a timing area plus where the student starts braking as compared to the starting gate.

The student pays attention only to maintaining speed through the timing area and then only on his right hand front brake lever effort. The instructor determines the 'score' (in the BRC, whether the student achieves about a 0.6g stop or not, and how many feet in excess of the target distance.)

Obviously, this thread is meant for the experienced rider who wants to improve his braking ability. He still needs his target distance marks on the ground, and an estimate of speed when he hits the starting gate. But let's say that he 'almost makes' 0.8g's with his efforts (assuming that's his target). This method shows him how to do better, not at braking, but at getting his brakes to start to work for him. If he merely maintains the same amount of braking pressure as he was using before attempting to 'squeeze quicker', achieving his objective becomes easier. In fact, now he can achieve his objective with less maximum braking pressure.

This is material for the second volume of the book - obviously.

What this material is demonstrating is that if you can achieve an average deceleration rate of 0.8g's during a 20 mph quick stop, the same braking effort will result in your achieving an average deceleration rate in excess of 0.9g's when you emergency stop at any speed greater than about 30 mph. And that improvement is free!
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aidanspa
Male Advanced Member
1739 Posts
[Mentor]


Omaha, NE
USA

Harley-Davidson

Road King

Posted - 11/23/2010 :  3:24 PM
quote:
Originally posted by James R. Davis

Jerry...

If he merely maintains the same amount of braking pressure as he was using before attempting to 'squeeze quicker', achieving his objective becomes easier. In fact, now he can achieve his objective with less maximum braking pressure.
Excellent. And you can call me anything except late for dinner.
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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/23/2010 :  3:39 PM Follow poster on Twitter  Join poster on Facebook as Friend  
Oops. Sorry, I corrected it.
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Axiom2000
Male Moderator
1761 Posts
[Mentor]


Georgetown, Delaware
USA

BMW

F 800 GT

Posted - 11/23/2010 :  4:16 PM
James,

quote:
What this material is demonstrating is that if you can achieve an average deceleration rate of 0.8g's during a 20 mph quick stop, the same braking effort will result in your achieving an average deceleration rate in excess of 0.9g's when you emergency stop at any speed greater than about 30 mph. And that improvement is free!


Very good stuff here, thought provoking.

Very few things of much worth are free, this is great free thing.

I think given the difference a few 10ths of a second makes to achieve maximum squeeze and then compare that to how quick a "Hand-full" may be, points out to just how important braking PLP is for anyone.




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gymnast
Moderator
4267 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 11/23/2010 :  4:32 PM
Among all the skills that are needed to competently (and safely) operate a motorcycle, braking skills are the most important and, in my opinion, the most overlooked. Jim, the charts, graphs, and explanations in your above post are a excellent resource that should see a great amount of use by those seeking to improve their performance as well as teach braking skills to others.
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radan2
Male Advanced Member
1117 Posts
[Mentor]


Jacksonville, NC
USA

Moto Guzzi

2007 Breva V750 ie

Posted - 11/23/2010 :  8:49 PM
I am constantly amazed when I read what James writes about how obvious it all seems AFTER he 'splained it.
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PopPop
Male Junior Member
47 Posts


Wilmington, DE
USA

Honda

2011 Kawi Concours14

Posted - 11/23/2010 :  10:45 PM
James, thank you for these great resources! I wish there was a way I could encourage all of the coaches I teach with to look at this information and then use it in a way that would help them to encourage their students in the BRC to improve their braking performance. Too many coaches are OK with just having their students meet the "standard" as defined by MSF and that is not good enough to ride on the street. Passing the class should not be their goal, getting the skills they need to ride on the street should be.
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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/25/2010 :  8:07 AM Follow poster on Twitter  Join poster on Facebook as Friend  
For those of you still convinced that some highly skilled riders can achieve an average deceleration rate of 1.2g's when stopping from 20 mph, you will need to be able to explain how a motorcycle's tires can support deceleration rates of nearly 1.5g's without losing traction. (It takes only 0.8 seconds and 11.1 feet to stop if you average 1.2g's.)



This is a much more likely representation of what happens when you 'squeeze too hard' trying for a world record quick stop.



Note that most bikes will do an end-over if they were to achieve a deceleration rate in excess of about 1.3g's (sport bikes may do an end-over at rates substantially lower than that.) The chart above assumes that an end-over does not occur.

There is nothing safe about trying to establish a world-record setting quick stop. A competent rider should establish and maintain the ability to average a deceleration rate of 0.8g's from 20 mph, and not much more than that even if he is a 'perfectionist'.
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CaptCrash
Male Advanced Member
744 Posts
[Mentor]


Nampa, ID
USA

Honda

Phantom

Posted - 11/25/2010 :  2:38 PM
Where I'm from "Grabbing a handful" is typically used as a negative to describe sudden, violent over-braking on the front, and occasionally used to describe violent application of throttle.

I've quite taken with the idea of how FAST you need to load the front--the idea of getting to max application while counting "one thousand one" has been batted around before and I've always shook my head and thought "Zikes! That's a long time".

Personally I enjoy stopping from 30 a great deal more than stopping from 20. At 20 I end up with rear tire in the air, having to relax my grip to put it down and then going long on my stops. At 30 I can get the front end down and 'float' the rear while not experiencing the fear of an endo. It raises the question in my mind to ask, when DO braking mistakes happen--particularly skidding and losing the front? My anecdotal, personal experience is that my stops from 20 are far uglier than my stops from 30...This leads me to wonder if that old axiom "there are 2 kinds of riders, those that have crashed and those that will" comes from all those low speed, grab a handful and tuck the front kinds of things illustrated by the red asterisks in James above diagram...

*added content: Perhaps the LOW speed "Grab a Handful" crash is where the common urban legend "the front brake kills you" finds it's roots as well...

Edited by - CaptCrash on 11/25/2010 2:48 PM
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Texasphotographer
Male Advanced Member
896 Posts
[Mentor]


Copperas Cove, Texas
USA

Honda

2006 GL1800 Trike

Posted - 11/25/2010 :  8:34 PM
Back in June 2008, when a cage ran a red light I only learned too well what "grabbing a handful" meant. I was turning right when I saw the cage out of my left eye. At that time, I grabbed rather violently the front brake and, while in the turn the bike lost traction and I went down. I broke 5 bones in my leg (3) and two in the ankle. Spent the next several months reading this forum and The Profecient Motorcyclist. The entire time, I was practicing squeeazing a makeshift front brake device a friend made for me. This device had a small amount of reverse pressure that allowed me practice squeezing and when I was cleared to ride this squeezing instead of grabbing was ingrained into me and this paid off when I started doing PLP again.

It is absolutely amazing what we learn here and even though I am now on three wheels much of the lessons taught here apply totally.

I am quite proud to say I have about 13,000 miles of happy miles on my trike since January 31, 2010.
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bachman1961
Male Advanced Member
2266 Posts
[Mentor]


colorado springs, co
USA

Honda

CB750 NightHawk

Posted - 11/27/2010 :  4:03 AM
James;

Not advocating PLP at higher speeds but I am interested in results for a 60 mph .3 .5 and .7 squeeze time to show it on paper.

Can you expand the chart to show the results or give me a formula to work it out?

~brian
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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/27/2010 :  9:23 AM Follow poster on Twitter  Join poster on Facebook as Friend  
The formula is simply:

Time to get to max rate * one half of max rate + time during max rate * max rate = deceleration ratetime

Since it takes 3.4 seconds to stop from 60 mph at an average deceleration rate of 0.8g's, the total deceleration ratetime is 3.4 * 0.8 = 2.72 g seconds.

Assuming 0.3 seconds to reach max deceleration rate:

(0.3 * 0.5)X + 3.1X = 2.72
0.15X + 3.1X = 2.72
3.25X = 2.72
X = 0.84g's




Assuming 0.5 seconds:

(0.5 * 0.5)X + 2.9X = 2.72
0.25X + 2.9X = 2.72
3.15X = 2.72
X = 0.86g's




Assuming 0.7 seconds:

(0.7 * 0.5)X + 2.7X = 2.72
0.35X + 2.7X = 2.72
3.05X = 2.72
X = 0.89g's

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bachman1961
Male Advanced Member
2266 Posts
[Mentor]


colorado springs, co
USA

Honda

CB750 NightHawk

Posted - 11/28/2010 :  12:53 AM

James;

Thank you for the formula and for taking the time to work it out showing the results! You obviously know of my engineering talents (how drained I am after un-packaging batteries or testing 600 light bulbs in the past few days) ... but still, you didn't go and tell everybody thus I am saved

A while back on another thread, I recall the topic of Perception, Decision and Reaction (PDR elapsed time) to be factored in as a part of the total in stopping distance. Now I can go back and look for evidence of 'the squeeze' duration to see if that was considered since I don't remember. It was probably identified in other terms.

Maybe 'one full second'. NUTS!!! you elude to in the opening of this post is a general number thrown in for a conservative consideration in the total stopping distance.
If so, the difference you point out in the .7 (max) for a competent rider to the 1.0 second example 'they' toss around is a very comforting margin of safety. At 1.46 fps this would be stopping over 20 feet shorter (26?) at 60 mph when shaving off that .3 of a second. Nice !

Seeing things in this respect makes me appreciate the higher degree of skills and expectations in our own performance because the 'yield' is a very sobering difference on the open road where we are sometimes far from help or emergency services. I'll take that extra .3 any day and hope I don't need it!

~brian
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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/28/2010 :  12:18 PM Follow poster on Twitter  Join poster on Facebook as Friend  
quote:
If so, the difference you point out in the .7 (max) for a competent rider to the 1.0 second example 'they' toss around is a very comforting margin of safety. At 1.46 fps this would be stopping over 20 feet shorter (26?) at 60 mph when shaving off that .3 of a second. Nice !


I had hopes that the message learned here was NOT that one, as it is definitely not true.

Whether you had a 0.3, 0.5, or 0.7 second time to get to your max deceleration rate, if you attained an average 0.8g deceleration rte (AND ONLY IF YOU DID) would you stop in 3.4 seconds taking the same 150 feet to do so.

The message I've been trying to get across is that the longer it takes you to get to your maximum deceleration rate, the HARDER IT IS to attain that average.

This 'squeeze time' is NOT a part of PDR. PDR precedes the braking effort. As soon as braking begins, you are no longer in the PDR time window.

Coupling good reflexes with high attentiveness and covering your brakes shortens the distance you travel before braking begins. A fast squeeze makes stopping easier.
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bachman1961
Male Advanced Member
2266 Posts
[Mentor]


colorado springs, co
USA

Honda

CB750 NightHawk

Posted - 11/29/2010 :  1:46 AM

I didn't intend to side step your point or mislead and, Thank you for the correction / clarification so I and others don't miss the correct message.

I think I was a bit too focused on the distance traveled after PDR and over the .3 or greater squeeze times. I brought up PDR to remind myself it is part of the real-world process in stopping distance as a precursor and that's where I drifted off the subject of times and g-forces.

Your closing really ties it together well in that short description for me;
Coupling good reflexes.... with high attentiveness and covering your brakes shortens the distance you travel before braking begins. A fast squeeze makes stopping easier.

~brian
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James R. Davis
Male Administrator
17292 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/29/2010 :  6:47 AM Follow poster on Twitter  Join poster on Facebook as Friend  
Brian,

Whoa! We are stepping on each others messages here - quite unintentionally, but I'm sure causing others some confusion.

All I tried to do with my last was separate the effects of a quick squeeze and PDR, which is what I thought your earlier post was trying to merge.

But your conclusion that a quicker squeeze results in a shorter stopping distance is absolutely correct if you merely use the same maximum braking force regardless of how quickly you get there.

An overall summary, from my perspective, is that you should do parking lot practices with the objective of being able to consistently achieve a deceleration rate of at least 0.8g's when starting at 20 mph. When you have gotten as good as you're going to get doing your practices, you can improve your performance even farther by changing your focus from attaining a certain stopping distance to achieving a faster squeeze time. The result will be that your average deceleration rate will increase.

While out on the road, when you do an emergency stop, that practicing effort will yield even better results because the length of time you are decelerating at your maximum rate is a substantially greater proportion of total stopping time than it was when braking from only 20 mph.

Finally, to stop even more quickly during an emergency you need to make your PDR time as small as possible. You do that by not allowing yourself to be distracted, by being healthy and not 'impaired' (for fast reflexes), by being pre-disposed to brake in response to virtually any threat (to minimize any decision time), and by covering your front brake lever.

I apologize for stepping on your message - I was only trying to separate PDR and quick squeeze time effects. But this message allows all of our readers to see the big picture more clearly - I hope.
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bachman1961
Male Advanced Member
2266 Posts
[Mentor]


colorado springs, co
USA

Honda

CB750 NightHawk

Posted - 11/29/2010 :  7:07 AM

No apology necessary but thanks for the offer !

I get caffeined up at night, this and my head is entirely too small to fit much of these subjects in.
As a result I speak (write) before I think (or read and understand) ... therein lies the problem or in this case, the challenge for James.

~brian
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(Deleted or Lost)

Posted - 11/29/2010 :  11:21 AM
quote:
Originally posted by bachman1961


No apology necessary but thanks for the offer !

I get caffeined up at night, this and my head is entirely too small to fit much of these subjects in.
As a result I speak (write) before I think (or read and understand) ... therein lies the problem or in this case, the challenge for James.

~brian


I think most of us are 'a challenge for James'.
Good thing, too, we probably do our part in keeping the ' grumpy old fogey' alert and focused, to everyone's benefit... If it wasn't for our 'creative' misunderstandings , his wisdom wouldn't stay as sharply aimed at being understandable by all.
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scottrnelson
Advanced Member
6890 Posts
[Mentor]


Pleasanton, CA
USA

KTM

990 Adv, XR650L

Posted - 12/02/2010 :  3:05 PM
Finally back from vacation...

I wanted to make one comment on the amount of time it takes to achieve maximum braking. On the two Ducatis that I owned for many years and sold at the end of the summer, it was possible to achieve maximum braking forces quite quickly. The suspension would only compress an inch or two before everything was settled and the front tire could get to its maximum braking force.

However, with my current bikes, there is a great deal more suspension travel. My KTM has a bit over 8 inches of suspension travel front and rear and the Honda XR650L is over 11 inches front and rear. It takes a little bit longer to get the bike to settle into a steady position for maximum braking. If the front brake is applied full force before the forks have compressed, the amount of weight on the front wheel will be less initially, then increase as the full weight of bike and rider compress the springs to the maximum amount, then it will decrease slightly as the front end rebounds to its final position. (Or at least, that is my opinion, I have no proof.)

This might not really matter on the KTM, since it has ABS, but could make a bigger difference on the Honda. But the Honda has weaker brake with one rather small disc on the front wheel, so maybe it's not an issue there either. But still, neither of those bikes will have the suspension settled in 0.3 seconds. It's going to be closer to 0.7 seconds to get them settled.
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