Can Disk Brakes flip you over the handle bars?

DougC

jobst.brandt@stanfordalumni.org wrote:
>
> I think you should read the FAQ item first at:
>
> http://www.sheldonbrown.com/brandt/over-the-bars.html
>
> before giving the usual endless pitch about the superiority of
> recumbents. Going over the bars, especially with disk brakes, is
> highly unlikely to be caused by locking the front wheel, but rather
> follows the scenario described in the FAQ.
>

The problem with the concept of "bracing with the arms" to use the front
brake of an upright bicycle is that--by nature--most crashes are
basically unanticipated. That's why there's crashes.

And as I noted--a bicycle doesn't need to tip completely over forward to
be unsafe during a panic stop. Merely un-weighting the rear tire enough
for the rear end to swing out left or right can result in a crash.

This is easy to demonstrate on pretty much any upright bicycle with
decent front brakes, and just about impossible to do on any
long-wheelbase recumbent. If one is worried about "going over the bars"
during a panic stop, it *IS* possible to pick a bicycle that basically
won't ever do it.
~

Ron Ruff

On May 1, 2:33*am, "mike.a.sch...@gmail.com" <mike.a.sch...@gmail.com>
wrote:
> Disk brakes have more stopping power and any such 'stomp' can result
> in a flip, not requiring any irregularities. *Due to their design,
> recumbents are immune from such a flip.

Even regular road brakes are strong enough to do this.

DougC

TBerk wrote:
>
> Yeah, I have a feeling a got one of them on the line right now.
>
>
> TBerk

The difference is between someone telling you it's your fault and to fix
the bike and keep riding,

and someone else telling you there's another kind of bike that this sort
of thing /never/ happens on, and that you can't even /make/ it happen if
you /try/.

------

Recumbents aren't better at all things but they have significant
advantages in several aspects, and emergency braking tends to be one of
them.
~

JG

> Disk brakes have more stopping power and ...

No they don't. Every unassisted brake system has the energy from your
two hands to work with to drive rubber pads into the rotor or rim.
You can make this more or less efficient, but you can't change this
fundamental limitation.

JG

Harry Brogan

On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
<landotter@gmail.com> wrote:

>On Apr 30, 10:49 pm, TBerk <bayareab...@yahoo.com> wrote:
>> Obviously I would assume they could if you clamp down fast enough.
>
>Yes, if you don't brace yourself and are unfamiliar with the brake and
>grab wildly, any powerful brake can be dangerous--but so can many
>things in life. Well adjusted brakes should be easy to modulate,
>provided you're not inebriated and have practiced a few panic stops,
>and shouldn't necessitate the purchase of a new bicycle.
>
>Be careful when posting questions like this, because you may attract
>'bent riders, who are bearded hammers in search of nails--sometimes
>with orange flippy flags!


I do NOT have orange flippy flags!!!!!! ROFLMAO
__o | Every time I see an adult on a bicycle....
_`\(,_ | I no longer despair for the human race.
(_)/ (_) | ---H.G. Wells---

landotter

On May 1, 12:51 pm, Harry Brogan
<hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
>
> <landot...@gmail.com> wrote:
> >On Apr 30, 10:49 pm, TBerk <bayareab...@yahoo.com> wrote:
> >> Obviously I would assume they could if you clamp down fast enough.
>
> >Yes, if you don't brace yourself and are unfamiliar with the brake and
> >grab wildly, any powerful brake can be dangerous--but so can many
> >things in life. Well adjusted brakes should be easy to modulate,
> >provided you're not inebriated and have practiced a few panic stops,
> >and shouldn't necessitate the purchase of a new bicycle.
>
> >Be careful when posting questions like this, because you may attract
> >'bent riders, who are bearded hammers in search of nails--sometimes
> >with orange flippy flags!
>
> I do NOT have orange flippy flags!

Yellow?

A Muzi

>> TBerk <bayareab...@yahoo.com> wrote:
>>> Obviously I would assume they could if you clamp down fast enough.

> landotter <landotter@gmail.com> wrote:
>> Yes, if you don't brace yourself and are unfamiliar with the brake and
>> grab wildly, any powerful brake can be dangerous--but so can many
>> things in life. Well adjusted brakes should be easy to modulate,
>> provided you're not inebriated and have practiced a few panic stops,
>> and shouldn't necessitate the purchase of a new bicycle.
>> Be careful when posting questions like this, because you may attract
>> 'bent riders, who are bearded hammers in search of nails--sometimes
>> with orange flippy flags!

Harry Brogan wrote:
> I do NOT have orange flippy flags!!!!!! ROFLMAO

Not yet?
Tom Sherman can probably help you choose a nice flippy orange one.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

Ben C

On 2008-05-01, JG <jchg@cox.net> wrote:
>> Disk brakes have more stopping power and ...
>
> No they don't. Every unassisted brake system has the energy from your
> two hands to work with to drive rubber pads into the rotor or rim.
> You can make this more or less efficient, but you can't change this
> fundamental limitation.

You sort of can, with leverage.

It's not really the energy from your hands that's important, but the
force they can apply. That force can be geared up to give you as much
force as you want on the rim/disk.

You need four times as much force on a disk because it has about a
quarter the radius of the wheel. But in either case you just gear it so
it feels right for people with averagely normal hand strength. This
isn't the difficult part of brake design.

Lots of cars didn't used to have servo assistance on the brakes. All the
force and work required to brake came from your leg. And yet you could
slow down a tonne of car from 70mph like that.

The difficult part is getting rid of all the heat that the brakes are
converting the bike's kinetic energy into.

Bicycle rims have enough heat capacity to just soak up the heat for most
stopping situations, but they can overheat badly if you need to keep
them on continuously because you want to go down a hill quite slowly.

Disks have less capacity, but get hotter, so dissipate heat to the air
more rapidly. So I reckon they're better for sustainable braking down
long hills.

But for emergency stops either kind of brake (of decent quality and
level of maintenance) will be able to tip you over the handlebars if you
aren't careful.

Harry Brogan

On Thu, 1 May 2008 11:21:35 -0700 (PDT), landotter
<landotter@gmail.com> wrote:

>On May 1, 12:51 pm, Harry Brogan
><hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
>> On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
>>
>> <landot...@gmail.com> wrote:
>> >On Apr 30, 10:49 pm, TBerk <bayareab...@yahoo.com> wrote:
>> >> Obviously I would assume they could if you clamp down fast enough.
>>
>> >Yes, if you don't brace yourself and are unfamiliar with the brake and
>> >grab wildly, any powerful brake can be dangerous--but so can many
>> >things in life. Well adjusted brakes should be easy to modulate,
>> >provided you're not inebriated and have practiced a few panic stops,
>> >and shouldn't necessitate the purchase of a new bicycle.
>>
>> >Be careful when posting questions like this, because you may attract
>> >'bent riders, who are bearded hammers in search of nails--sometimes
>> >with orange flippy flags!
>>
>> I do NOT have orange flippy flags!
>
>Yellow?


FUNNY!!!!......No....not yellow either.....Here's a photo....

http://i255.photobucket.com/albums/...01012003_02.jpg


__o | Every time I see an adult on a bicycle....
_`\(,_ | I no longer despair for the human race.
(_)/ (_) | ---H.G. Wells---

jobst.brandt@stanfordalumni.org

Ben C? wrote:

>>> Disk brakes have more stopping power and...

>> No they don't. Every unassisted brake system has the energy from
>> your two hands to work with to drive rubber pads into the rotor or
>> rim. You can make this more or less efficient, but you can't
>> change this fundamental limitation.

> You sort of can, with leverage.

As is apparent, leverage cannot be arbitrarily changed without other
effects that require difficult redesign. Dual pivot rim brake
calipers are a classic example. To achieve the higher MA required by
today's riders pad clearance had to be reduced and this required
forced centering to prevent brake drag. Disks have the same problem.

> It's not really the energy from your hands that's important, but the
> force they can apply. That force can be geared up to give you as
> much force as you want on the rim/disk.

In what units are you measuring "energy" or do you mean "force"?

> You need four times as much force on a disk because it has about a
> quarter the radius of the wheel. But in either case you just gear it
> so it feels right for people with averagely normal hand
> strength. This isn't the difficult part of brake design.

That isn't the parameter of interest. Disk diameter and coefficient
of friction both have a major effect on the ratio between application
force and brake torque.

> Lots of cars didn't used to have servo assistance on the brakes.
> All the force and work required to brake came from your leg. And
> yet you could slow down a tonne of car from 70mph like that.

Drum brakes used massive self servo action to achieve useful braking.
Because that effect is highly unpredictable, they had both lock-up and
fade. That is why we use disks today. You may recall that this was
discussed here at great length.

> The difficult part is getting rid of all the heat that the brakes
> are converting the bike's kinetic energy into.

Apparently the bicycle industry is not addressing that part of the
problem when the surface area and thermal mass their gossamer rings of
steel have. I have asked brake manufacturers why their disks are
mostly air with a thin pattern of thin steel between. For cooling is
the answer. Maybe they should tell the automotive and railway people
about their theory.

> Bicycle rims have enough heat capacity to just soak up the heat for
> most stopping situations, but they can overheat badly if you need to
> keep them on continuously because you want to go down a hill quite
> slowly.

It depends on gradient that gives (vertical) foot (rider weight
(pounds) per second. The slower you go the less cooling and the less
wind drag on the rider. There is a narrow trade-off between brake
cooling and speed which was discussed here recently.

> Disks have less capacity, but get hotter, so dissipate heat to the
> air more rapidly. So I reckon they're better for sustainable
> braking down long hills.

By that measure, a wafer thin disk is all it takes, surface area and
mass be damned.

> But for emergency stops either kind of brake (of decent quality and
> level of maintenance) will be able to tip you over the handlebars if
> you aren't careful.

I doubt it. I don't know many riders who can raise the rear wheel
while traveling at normal road speeds. In contrast, I have seen
people go over the bars:

http://tinyurl.com/3kunfl

Jobst Brandt

_

On Thu, 01 May 2008 12:02:27 -0500, DougC wrote:

> jobst.brandt@stanfordalumni.org wrote:
>>
>> I think you should read the FAQ item first at:
>>
>> http://www.sheldonbrown.com/brandt/over-the-bars.html
>>
>> before giving the usual endless pitch about the superiority of
>> recumbents. Going over the bars, especially with disk brakes, is
>> highly unlikely to be caused by locking the front wheel, but rather
>> follows the scenario described in the FAQ.
>>
>
> The problem with the concept of "bracing with the arms" to use the front
> brake of an upright bicycle is that--by nature--most crashes are
> basically unanticipated. That's why there's crashes.
>
> And as I noted--a bicycle doesn't need to tip completely over forward to
> be unsafe during a panic stop. Merely un-weighting the rear tire enough
> for the rear end to swing out left or right can result in a crash.
>

Or, like the Raptor trike, be badly designed - that one had a very small
bolt loaded in shear about 1" from the front wheel axle as a means of
controlling brake torque. It broke when the ten-year old was riding it;
the steering arm went forward pulling him over the front wheels and out of
the trike; fortunately he was on the pavement at the time.

It's been fixed now; the brake torque is now taken by a triangluted
arrangement that is much larger and much stronger, with only a few ounces
additional weight.

landotter

On May 1, 6:47 pm, Harry Brogan
<hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> On Thu, 1 May 2008 11:21:35 -0700 (PDT), landotter
>
>
>
> <landot...@gmail.com> wrote:
> >On May 1, 12:51 pm, Harry Brogan
> ><hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> >> On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
>
> >> <landot...@gmail.com> wrote:
> >> >On Apr 30, 10:49 pm, TBerk <bayareab...@yahoo.com> wrote:
> >> >> Obviously I would assume they could if you clamp down fast enough.
>
> >> >Yes, if you don't brace yourself and are unfamiliar with the brake and
> >> >grab wildly, any powerful brake can be dangerous--but so can many
> >> >things in life. Well adjusted brakes should be easy to modulate,
> >> >provided you're not inebriated and have practiced a few panic stops,
> >> >and shouldn't necessitate the purchase of a new bicycle.
>
> >> >Be careful when posting questions like this, because you may attract
> >> >'bent riders, who are bearded hammers in search of nails--sometimes
> >> >with orange flippy flags!
>
> >> I do NOT have orange flippy flags!
>
> >Yellow?
>
> FUNNY!!!!......No....not yellow either.....Here's a photo....
>
> http://i255.photobucket.com/albums/...%20Rig/1000Mile...

You could accent Old Glory with an international Pantheon of flippy
flags! Might affect your aerodynamics.

clare at snyder dot ontario dot canada

On Thu, 1 May 2008 01:33:03 -0700 (PDT), "mike.a.schwab@gmail.com"
<mike.a.schwab@gmail.com> wrote:

>On Apr 30, 10:49 pm, TBerk <bayareab...@yahoo.com> wrote:
>> Obviously I would assume they could if you clamp down fast enough.
>>
>> I ask because I bruised some rib bones this week when I stomped the
>> front brake and *surprise* I found out later my front rim has a bubble
>> bend in it from (I guess) a pot hole at some recent time.
>>
>> Made for a portion of the rim that just wasn't going to get past the
>> brake pads, not while I was trying to actually use said brakes.
>>
>> It would seem a better setup would be one unaffected by a slightly
>> bent rim, or so I wonder.
>>
>> TBerk
>> it would have been funny if it hadn't hurt so much at the time
>
>Disk brakes have more stopping power and any such 'stomp' can result
>in a flip, not requiring any irregularities. Due to their design,
>recumbents are immune from such a flip.


Even the relatively ineffectual old "atom" drum brake could "unhorse"
you under the right circumstances.
** Posted from http://www.teranews.com **

Tom Sherman

mike.a.schwab@gmail.com aka Mike Schwab wrote:
> On Apr 30, 10:49 pm, TBerk <bayareab...@yahoo.com> wrote:
>> Obviously I would assume they could if you clamp down fast enough.
>>
>> I ask because I bruised some rib bones this week when I stomped the
>> front brake and *surprise* I found out later my front rim has a bubble
>> bend in it from (I guess) a pot hole at some recent time.
>>
>> Made for a portion of the rim that just wasn't going to get past the
>> brake pads, not while I was trying to actually use said brakes.
>>
>> It would seem a better setup would be one unaffected by a slightly
>> bent rim, or so I wonder.
>>
>> TBerk
>> it would have been funny if it hadn't hurt so much at the time
>
> Disk brakes have more stopping power and any such 'stomp' can result
> in a flip, not requiring any irregularities. Due to their design,
> recumbents are immune from such a flip.

Recumbents with PROPER weight distribution will skid the front wheel
instead of sending the rider over the bars. Some early bad designs, such
as the Hypercycle, would send the rider off the front under heavy
braking, and had too little weight on the rear wheel for it to provide
much braking.

I often wonder if the Hypercycle and its ilk are responsible for much of
the negative attitudes towards recumbents by certain riders. Certainly,
if a rider's only experience was the ill handling, poor climbing and
poor braking Hypercycle, they would not look kindly on recumbents as a
whole.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful