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Braking Technique



 
 
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  #1  
Old July 16th 03, 02:57 PM
asqui
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Default Braking Technique

In the footage of Beloki's spectacular crash it can be seen that Armstrong
briefly locks up his rear wheel as Beloki crashes. I thought on a decent
surface the best way to stop was front brake only? I guess that was feasible
with the Weinmann brakes on my Eddy Meckx but these Tektro cantilevers leave
some braking performance to be desired . Anyway, obviously on a descent
like that you'll want to use both to distribute the rim heating evenly, but
why did Lance lock up the rear? In the emergency situation shouldn't he have
been using the front brake exclusively -- exactly for the reason of avoiding
a rear wheel skid?

(I will agree that front brake only is a little "eggs in one basket" because
if you wash out the front you're pretty much gone, but I'm arguing based on
the "front brake only" rule I've heard time and time again.)

Dani


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  #2  
Old July 16th 03, 03:39 PM
rayneman
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Default Braking Technique

Dani, try this... Go out and find a big hill, get going really fast and
grab your front brake, hard as you can like you would in an emergency
situation. When you get out of the hospital, write back and let us know
how it works.
Thanks,
Ray

asqui wrote:
In the footage of Beloki's spectacular crash it can be seen that Armstrong
briefly locks up his rear wheel as Beloki crashes. I thought on a decent
surface the best way to stop was front brake only? I guess that was feasible
with the Weinmann brakes on my Eddy Meckx but these Tektro cantilevers leave
some braking performance to be desired . Anyway, obviously on a descent
like that you'll want to use both to distribute the rim heating evenly, but
why did Lance lock up the rear? In the emergency situation shouldn't he have
been using the front brake exclusively -- exactly for the reason of avoiding
a rear wheel skid?

(I will agree that front brake only is a little "eggs in one basket" because
if you wash out the front you're pretty much gone, but I'm arguing based on
the "front brake only" rule I've heard time and time again.)

Dani



  #3  
Old July 16th 03, 04:03 PM
Callistus Valerius
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Default Braking Technique


Dani, try this... Go out and find a big hill, get going really fast and
grab your front brake, hard as you can like you would in an emergency
situation. When you get out of the hospital, write back and let us know
how it works.
Thanks,
Ray


what foolishness, everyone knows it's both brakes.


  #4  
Old July 16th 03, 04:35 PM
asqui
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Default Braking Technique

Callistus Valerius wrote:
Dani, try this... Go out and find a big hill, get going really fast
and grab your front brake, hard as you can like you would in an
emergency situation. When you get out of the hospital, write back
and let us know how it works.
Thanks,
Ray


what foolishness, everyone knows it's both brakes.


The argument I have heard is thus:

Since the center of gravity of the human-bike system is higher than the
wheel-road interface (which provides the braking force) the human-bike
system has the tendency to pitch forward with braking, causing weight
transfer to the front wheel.
Hence the theoretical scenario for maximal braking would be that the braking
is sufficient to transfer all weight to the front wheel, leaving the rear
wheel with zero force on the ground. At this point any increase in braking
force of the front wheel would cause the rear wheel to lose contact with the
ground, and braking on the rear wheel would cause the it to skid and
increase the chances of the rider losing control.

This assumes that the front wheel has sufficient friction with the road (in
order to not skid) and brake blocks (in order to receive the necessary
braking force).

As for the experiment, I've already carried it out -- steep downhill, amber
light, car in front stops. I managed to stop about a meter behind said car,
with my rear wheel off the ground and trying to overtake me. I think that
was because I was out of the saddle and didn't sit down on it properly as I
was braking. Ideally I would have sat down and shifted my weight back to
keep the rear wheel on the ground and increase my stability.

What do you think?

Dani


  #5  
Old July 16th 03, 04:56 PM
Daniel Connelly
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Default Braking Technique

asqui wrote:
Callistus Valerius wrote:
The argument I have heard is thus:

Since the center of gravity of the human-bike system is higher than the
wheel-road interface (which provides the braking force) the human-bike
system has the tendency to pitch forward with braking, causing weight
transfer to the front wheel.
Hence the theoretical scenario for maximal braking would be that the braking
is sufficient to transfer all weight to the front wheel, leaving the rear
wheel with zero force on the ground. At this point any increase in braking
force of the front wheel would cause the rear wheel to lose contact with the
ground, and braking on the rear wheel would cause the it to skid and
increase the chances of the rider losing control.

This assumes that the front wheel has sufficient friction with the road (in
order to not skid) and brake blocks (in order to receive the necessary
braking force).

As for the experiment, I've already carried it out -- steep downhill, amber
light, car in front stops. I managed to stop about a meter behind said car,
with my rear wheel off the ground and trying to overtake me. I think that
was because I was out of the saddle and didn't sit down on it properly as I
was braking. Ideally I would have sat down and shifted my weight back to
keep the rear wheel on the ground and increase my stability.

What do you think?


In real world conditions, uncertainty in the current state of the
system, plus time-variation in the conditions, means it's not possible
to brake at the theoretical limit. This makes it prudent to
apply rear braking force, as well. As the deceleration increases, the
normal force at the rear tire/road contact decreases, decreasing the braking
force relative to what it would be if only the front brake was used.
OTOH, if all force is applied to the front brake, an increase in the
normal force at the front tire due to a momentary increase in the rate
of deceleration will have maximum positive feedback as braking force
is then increased. Positive feedback is destabilizing.

Result: hospitalization.

Dan

  #6  
Old July 17th 03, 02:11 AM
asqui
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Posts: n/a
Default Braking Technique

rayneman wrote:
Dani, try this... Go out and find a big hill, get going really fast
and
grab your front brake, hard as you can like you would in an emergency
situation. When you get out of the hospital, write back and let us
know
how it works.
Thanks,
Ray


If I was going to indiscriminately squeeze as hard as I possibly could on a
single lever, I don't think it would make any difference whether I skid the
front, skid the rear uncontrollably and slide, or possibly even fail to
brace my hands against the bars and fly over them before developing enough
braking force to skid the front wheel.

I was talking about effective braking technique, not how to hurt yourself by
panicking in an emergency and doing something rash.

The rec.bicycles.* faq (http://draco.acs.uci.edu/rbfaq/FAQ/9.17.html) and
Sheldon Brown (http://sheldonbrown.com/brakturn.html) are the most likely
candidates for where I heard about the front-brake-only technique. I hope
you will agree that they are both reputable sources and present the solid
justification for this technique.

Dani


  #7  
Old July 17th 03, 03:36 AM
S. Anderson
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Default Braking Technique

"asqui" wrote in message
...
rayneman wrote:

If I was going to indiscriminately squeeze as hard as I possibly could on

a
single lever, I don't think it would make any difference whether I skid

the
front, skid the rear uncontrollably and slide, or possibly even fail to
brace my hands against the bars and fly over them before developing enough
braking force to skid the front wheel.

I was talking about effective braking technique, not how to hurt yourself

by
panicking in an emergency and doing something rash.

The rec.bicycles.* faq (http://draco.acs.uci.edu/rbfaq/FAQ/9.17.html) and
Sheldon Brown (http://sheldonbrown.com/brakturn.html) are the most likely
candidates for where I heard about the front-brake-only technique. I hope
you will agree that they are both reputable sources and present the solid
justification for this technique.

Dani


Both the FAQ and Mr. Brown are correct and I don't think they advocate
front-brake only for max braking. Max braking is a slippery ideal. Even
with full concentration it's a tricky thing. Put the purple mist or sheer
panic into the mix and it's nearly impossible to achieve consistently. Max
braking does occur when the rear wheel is leaving the ground, effectively
making the rear brake useless. But it's a tricky thing to accomplish. So
unless the rear wheel is off the ground, the rear brake is making SOME
contribution, however very little it may be. It's a sliding scale, front
versus rear brake, depending on how much deceleration is occuring and how
much weight is on the rear wheel. In a situation like Beloki's crash, these
things can easily overwhelm even the best riders. We're talking about a guy
who makes his professional living climbing and descending mountains..I'm
sure he's well aware of braking techniques and maybe he was simply in a
situation that was impossible. There may have been just too much sensory
input to decode and he just made a mistake.

Incidentally, I hit the racetrack every now and again with my motorcycle and
I NEVER touch the rear brake when at the track. However, if you watch the
good guys, you can see them sliding the rear tire into corners using the
rear brake and engine braking. These guys are able to decode the input from
the bike to do those things. I'm simply overwhelmed with all the stuff
going on and cannot do the stuff they do. So your idea of front-brake only
may be analogous to my motorcycle situation..if you can't reliably operate
the rear brake during max braking so that the rear wheel doesn't skid,
you're probably better off using the front only.

Cheers,

Scott..


  #8  
Old July 17th 03, 04:02 AM
warren
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Default Braking Technique

In article , asqui
wrote:

warren wrote:
I think you should worry less about invalid "arguments" and spend the
time practicing with both brakes and keeping your weight farther back
under heavy braking. Don't you think that having two tires making
contact/friction with the ground would work better?

-WG


So yeah... now that I found out where I read this invalid argument perhaps
you would like to consult the rec.bicycles.* faq around he
http://draco.acs.uci.edu/rbfaq/FAQ/9.17.html
Eating one's hat is optional.


Look dude, 700+ criteriums and riding up and down the 15mph switchbacks
here in the Sierra foothills have taught me plenty about braking. It's
true that more braking force is used on the front wheel but you were
talking about putting none on the rear wheel, which is dumb.

Stay out of my way in the turns.

-WG
  #9  
Old July 17th 03, 05:12 AM
S. Anderson
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Posts: n/a
Default Braking Technique

"warren" wrote in message
...
In article , asqui
wrote:


Look dude, 700+ criteriums and riding up and down the 15mph switchbacks
here in the Sierra foothills have taught me plenty about braking. It's
true that more braking force is used on the front wheel but you were
talking about putting none on the rear wheel, which is dumb.

Stay out of my way in the turns.

-WG


700+ criteriums?? How many years have you been racing?? That's a bit of
practice to be sure! And you're right. Braking is a dynamic condition..the
amount of traction on either wheel is going to be variable depending on a
number of factors and save for that amazingly fine line where the rear wheel
begins to lift off, the rear wheel does contribute some braking.

Cheers,

Scott..


  #10  
Old July 17th 03, 02:53 PM
Zelda
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Default Steering (was Braking Technique)

Since you compare bicycles to motorcycles, I have a different
question:

I used to ride motorcycles, and tried amateur roadracing for a couple
of years. Last year, when I bought my first-ever good quality road
bicycle, I asked the staff at the bike shop if you use countersteering
to go around fast corners on a bicycle, as you do on a motorcycle
(pushing the handlebar away from you). They didn't know what I was
talking about.

So, do you use countersteering on a road bicycle?

Thanks,
Zelda

"S. Anderson" wrote in message ...
(snip)
Incidentally, I hit the racetrack every now and again with my motorcycle and
I NEVER touch the rear brake when at the track. However, if you watch the
good guys, you can see them sliding the rear tire into corners using the
rear brake and engine braking. These guys are able to decode the input from
the bike to do those things. I'm simply overwhelmed with all the stuff
going on and cannot do the stuff they do. So your idea of front-brake only
may be analogous to my motorcycle situation..if you can't reliably operate
the rear brake during max braking so that the rear wheel doesn't skid,
you're probably better off using the front only.

Cheers,

Scott..

 




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