Can Disk Brakes flip you over the handle bars?

TBerk

On May 1, 8:58 am, jobst.bra...@stanfordalumni.org wrote:
> The Berk 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!
> > Yeah, I have a feeling a got one of them on the line right now.
> > Folks, obviously if I had known the rim had a problem I would have
> > factored that in, either readjusting the brakes, massaging the rim,
> > drove around instead of stopping suddenly,and/or all of the above.
>
> Wait a minute. You started this thread with the heading about "disk
> brakes". How about getting the description consistent with the story.
> Besides, unless a rim is offset so there is a significant step in the
> alignment before and after a break, a ding in a rim will also not
> cause the front wheel to lock.
>
> You "went over the bars" in the usual manner and leave it at that.
>
> Jobst Brandt

You are no longer invited to bite me, in this case Big Green Donkeys
are your answer.

1) I am well aware of my conventional, on the rim, brakes.

2) I had a deformation of the rim that caused them to lock during a
sudden, but seemingly manageable stopping maneuver.

3) There is a question I posted to the newsgroup about alternative
brake systems; disk brakes.

There comes along a knucklehead who is confused about my posting but
seems to have figured out the mysteries of life... only I am not
paying him any mind.

Thanks most everybody else.


TBerk

TBerk

On May 1, 9:15 am, frkry...@gmail.com wrote:
<snip>
> BTW, I don't think that readjusting the brakes would help. No matter
> how much rim clearance they have when released, they're going to have
> zero rim clearance when you apply them.
>
> Disk brakes have their own problems. Rather than contemplating a
> switch, I think it's better to learn to care for your bike, and pay
> attention to the road. And I'm not trying to sound harsh. That's
> just the way it is.
>
> - Frank Krygowski

Good points.

The rim will need mending, no doubt. I might have adjusted the brakes
on the road to lessen the braking power. Just an option.

I contemplate a switch because my used frame has been in trouble for
awhile with some bent front forks. Replacing them pens up the option
of a disk brake capible setup.

No need to worry about sounding harsh, you veterans here don't know me
from Adam.

TBerk

jobst.brandt@stanfordalumni.org

Tom Sherman 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.

>>> 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've seen nay recumbents with a small front wheel and cranks and
pedals forward of that wheel. These units will endo easily while the
rider remains firmly in the seat. The advantage is that the rider, if
a bit agile, will land on his feet running. The bike does not fare as
well as it overturns and scraped the road.

> I often wonder if the Hypercycle and its ilk are responsible for
> much of the negative attitudes toward 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.

Long wheelbase recumbents have a slew of other problems in
maneuverability and climbing rough stuff. Disk brakes are not one of
their problems.

Jobst Brandt

Tom Sherman

jobst.brandt@stanfordalumni.org aka Jobst Brandt wrote:
> Tom Sherman 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.
>
>>>> 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've seen nay recumbents with a small front wheel and cranks and
> pedals forward of that wheel. These units will endo easily while the
> rider remains firmly in the seat.

Absolutely NOT true in my experience of short-wheelbase recumbent
bicycles with proper weight distribution (e.g. RANS Rocket, RANS V-Rex,
RANS Vivo, Lighting P-38, Burley HepCat, Reynolds Wishbone, and of
course the Earth Cycles Sunset).

On my Dragonflyer trike which has the crank ahead of the front wheels, I
can skid both on dry pavement without the rear wheel lifting.

How many modern short-wheelbase recumbent bicycles has Jobst Brandt
ridden to determine that "endos" are likely?

> The advantage is that the rider, if
> a bit agile, will land on his feet running. The bike does not fare as
> well as it overturns and scraped the road.
>
Mr. Brandt must be thinking of the Hypercycle or some other obsolete design.

>> I often wonder if the Hypercycle and its ilk are responsible for
>> much of the negative attitudes toward 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.
>
> Long wheelbase recumbents have a slew of other problems in
> maneuverability and climbing rough stuff. Disk brakes are not one of
> their problems.
>
Actually, front braking is more of a problem on a long-wheelbase
recumbent than a short-wheelbase recumbent, since it is much easier to
accidentally lock up the front wheel.

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

Tom Sherman

Doug Cimper 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.
> [...]

On a recumbent bicycle, the rider does not need to brace with his/her
arms to keep from going over the bars, as his/her legs are naturally in
a position to provide the required bracing.

The above would be obvious to someone who has actually ridden a properly
designed recumbent in real world settings.

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

Tom Sherman

landotter 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!
>
Since so many upright riders feel necessary to comment on the alleged
disadvantages of recumbents (often quite rudely in person), it is only
fair to do the same for uprights.

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

Tom Sherman

jobst.brandt@stanfordalumni.org aka Jobst Brandt wrote:
> Ben C? wrote:
> [...]
>> 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:[...]

It is much easier to lift the rear wheel if the bicycle has a suspension
fork. I can do "stoppies" quite easily on my Trek 6000, even with the
knobby tread tires.

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

TBerk

On May 1, 8:31 pm, Tom Sherman <sunsetss0...@REMOVETHISyahoo.com>
wrote:
> landotter wrote:
<snippage>
> > 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!
>
> Since so many upright riders feel necessary to comment on the alleged
> disadvantages of recumbents (often quite rudely in person), it is only
> fair to do the same for uprights.
>
> --
> Tom Sherman -

But yeah, you guys are thread-jacking though.


TBerk

Tom Sherman

TBerk ? wrote:
> On May 1, 8:31 pm, Tom Sherman <sunsetss0...@REMOVETHISyahoo.com>
> wrote:
>> landotter wrote:
> <snippage>
>>> 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!
>> Since so many upright riders feel necessary to comment on the alleged
>> disadvantages of recumbents (often quite rudely in person), it is only
>> fair to do the same for uprights.
>>
>> --
>> Tom Sherman -
>
> But yeah, you guys are thread-jacking though.
>
In other breaking news...

Thread drift is a fact of life on Usenet.

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

Zebee Johnstone

In alt.rec.bicycles.recumbent on Thu, 01 May 2008 22:28:25 -0500
Tom Sherman <sunsetss0003@REMOVETHISyahoo.com> wrote:
>
> On a recumbent bicycle, the rider does not need to brace with his/her
> arms to keep from going over the bars, as his/her legs are naturally in
> a position to provide the required bracing.

And on a recumbent with a hinged stem (such as my Bacchetta Giro)
bracing with the hands is a Bad Idea!

(as I found out on the test ride.....)

Zebee

Peter Clinch

jobst.brandt@stanfordalumni.org wrote:

> I've seen nay recumbents with a small front wheel and cranks and
> pedals forward of that wheel.

My Streetmachine has a 20" front wheel and the cranks ahead of it.

> These units will endo easily while the
> rider remains firmly in the seat.

For some values of "easily"... I find that if I slam on the anchors in
an emergency stop I get both wheels skidding, and no hint of an endo.

> The advantage is that the rider, if
> a bit agile, will land on his feet running. The bike does not fare as
> well as it overturns and scraped the road.

What happens in my direct experience on a Streetmachine is I skid to a
stop, still in the seat, still the right way up and think "!"
For me, direct empirical evidence trumps theory.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net p.j.clinch@dundee.ac.uk http://www.dundee.ac.uk/~pjclinch/

Ben C

On 2008-05-01, jobst.brandt@stanfordalumni.org <jobst.brandt@stanfordalumni.org> wrote:
[...]
>> 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"?

I'm not measuring energy but if I was I would use Joules.
I mean energy when I say "energy" and force when I say "force".

My point is that it takes very little energy from a rider to squeeze the
brakes. You have to move your fingers a short distance, but the main
requirement on your body is to maintain a force.

As discussed here previously continuous force maintenance by human
muscles does require the consumption of some energy, but it is only a
small amount.

>> 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.

Yes that too, but the basic point is the same: you give the user enough
mechanical advantage to give the brakes a satisfactory feel whether they
are disk brakes or rim brakes.

An overgeared brake isn't a better brake.

>> 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.

There were plenty of cars with non-servo-assisted disks too.

>> 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.

This is why I think that disks don't really work as heat sinks but as
dissipators.

Here are my various guesses and estimates on which I'm basing this:
http://groups.google.co.uk/group/uk...91d32532f671264

> I have asked brake manufacturers why their disks are
> mostly air with a thin pattern of thin steel between. For cooling is
> the answer.

Ah but did they mean because they _look_ cool

> Maybe they should tell the automotive and railway people about their
> theory.

I remember a calculation here before about cross-drilled disks on cars.

I think your point was originally to slay a herring about "gas
bearings", which was fair enough, but I think it was concluded also that
a drilled disk will have a slightly higher surface area to volume ratio
than one that isn't drilled.

Same goes for a filigreed disk. But I don't really buy that "it cools
better" line either. It would have to be shown by how much and also what
the effect of a smaller surface area in contact with the pad has (for
car disks, I think those filigreed bike disks usually have a continuous
undrilled track that touches the pads).

>> 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.

Indeed. For a given hill/bike there's a "worst speed" for heat buildup.
Descend either faster or slower than that speed and you're better off.

>> 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.

Well surface area affects its dissipation rate, which does need to be
high by this measure.

But mass be damned, provided the thing's strong enough.

>> 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

Nice picture of a pedal, what's it got to do with going over the
handlebars?

I agree that it's hard to do though. I shouldn't have said "if you
aren't careful"-- it's not a problem practically speaking on any bike
I've ridden.

Zebee Johnstone

In alt.rec.bicycles.recumbent on 02 May 2008 01:44:09 GMT
jobst.brandt@stanfordalumni.org <jobst.brandt@stanfordalumni.org> wrote:
> I've seen nay recumbents with a small front wheel and cranks and
> pedals forward of that wheel. These units will endo easily while the
> rider remains firmly in the seat. The advantage is that the rider, if
> a bit agile, will land on his feet running. The bike does not fare as
> well as it overturns and scraped the road.

Will they?

I've been hard on the picks (front disk even!) on my Giro 20 going
downhill. The back (v-brake) skidded, so I let up, I did my damndest not
to lock the front, and didn't (riding a motorcycle has some advantages)
but the thing showed no sign of an endo I could feel.

Indeed, trying same when I first got the disks didn't get me anywhere.
Locking the front is hard to do when you have trained for years not
to, so maybe I wasn't trying hard enough. Never felt a massive weight
transfer forward, nothing like pulling a stoppie on a motorcycle (which
I have done more than once).

If they will "endo easily" then I must be dreaming...

So I have to ask... have you ridden one? Have you managed to endo it?

If so, how? What did it feel like, when did the weight transfer get so
over rather than forward (hard transfer on a bent feels qualitatively
different to hard transfer on an upright to me), and how fast did you have
to go, and how fast were you going when you managed to get it to go over?


Zebee

Tom Sherman

Zebee Johnstone wrote:
> In alt.rec.bicycles.recumbent on Thu, 01 May 2008 22:28:25 -0500
> Tom Sherman <sunsetss0003@REMOVETHISyahoo.com> wrote:
>> On a recumbent bicycle, the rider does not need to brace with his/her
>> arms to keep from going over the bars, as his/her legs are naturally in
>> a position to provide the required bracing.
>
> And on a recumbent with a hinged stem (such as my Bacchetta Giro)
> bracing with the hands is a Bad Idea!
>
> (as I found out on the test ride.....)
>
I have had to brake very hard when cut off by idiot cagers while
descending fast (70+ kph) on my RANS Rocket with a Flip-It® hinged
handlebar riser, and the bars did not move forward. And I can move the
bars forward and back with one little finger while at rest.

I have had the same experience on several other short-wheelbase
recumbents with hinged risers. Basically, freely hinged handlebars can
NOT restrain the rider from moving forward until they hit their forward
stop, which is farther than the rider can reach while seated. So the
legs and friction between the rider and the seat have to be providing
all the restraining force to keep the rider on the bike while braking.

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