Can Disk Brakes flip you over the handle bars?

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

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

Doug Cimper wrote:
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

landotter wrote:
On Apr 30, 10:49 pm, TBerk 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

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

On May 1, 8:31 pm, Tom Sherman
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

TBerk ? wrote:
On May 1, 8:31 pm, Tom Sherman
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

In alt.rec.bicycles.recumbent on Thu, 01 May 2008 22:28:25 -0500
Tom Sherman 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

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 http://www.dundee.ac.uk/~pjclinch/

On 2008-05-01, 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....1d32532f671264

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.