Poor braking

Marz wrote on 23/06/2006 19:22 +0100:

Quoted message said:

Ok, I've done a poor job of explaining what I'm talking about. To
complete a bunny hop you need to push yourself down into the bike,
compressing the suspension and or tyres before exploding verticaly to
get lift.

That's the hard work way to do it, lifting the bike up physically. The
easy way is to move your weight back to lift the front wheel and then
push forwards on the bars to bring the back wheel up.

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

Tony Raven said:

That's the hard work way to do it, lifting the bike up physically. The
easy way is to move your weight back to lift the front wheel and then push
forwards on the bars to bring the back wheel up.

Ah yes. Yogic Flying for bicycles.

Was that you or the International Space Station I saw wizzing by last
night ;-)

Mike

Mike Causer wrote on 23/06/2006 22:10 +0100:

Quoted message said:

Was that you or the International Space Station I saw wizzing by last
night ;-)

That would have been Helen of this parish - often mistaken for a UFO
with her Sizewell powered night-time illuminations

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

Tony Raven said:

Phil Armstrong wrote on 23/06/2006 19:15 +0100:

Quoted message said:

It's been asserted elsewhere in this thread that rim brakes are
perfectly capable of reaching this limiting braking force.

Not on tandems ;-)

The pedants in the corner can pipe down 🙂

Phil

--
http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt

Marz said:

Phil Armstrong said:

As has been pointed out elsewhere in this thread, the limit of braking
is when the torque on the rider + bike due to the rider pushing
against the bars against the braking of the bike is just short that
required to lift the back wheel. Any more braking force will tip the
rider over the bars.

You shouldn't be pushing against the bars, the bars are for steering,
braking and shifting gear, most (98.7657%(yes I made it up)) of your
weight should be on your pedals.

Basic physics again: if you're at the limit, you have to be pushing
against the bars. Unless you can get your COG lower than the axle of
the front wheel then you have to have something to push against to
stop yourself going over the bars!

Quoted message said:

But a better braking technique increases the limit to a point (I've
found) beyond the capabilities of cable operated rim brakes. This is
based mostly through mtb experience rather than road riding.

I can believe that brakes with better 'feel' than rim brakes can let
you get closer to the limits with more control.

Quoted message said:

Bounce, once and down, if one can bounce down. All this [censored] from
me is going land me with face plant this weekend as I try prove my
point.

Do try not to faceplant on my account 🙂

Phil

--
http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt

Chris Eilbeck said:

Disks must have some advantages over rim brakes. The one I can see
would be that

Lots.

Quoted message said:

- your pads are pressing flat against a disk and compressing it rather
than pressing on the sides of a u-section rim.

- you have separate mechanical system for supporting the rider (the
wheel rim) and the braking system, which will have different and
probably competing design goals.

- you can run disks hotter, no need to keep them cool because you've
got a a tyre in contact with the braking surface.

Disks just seem like a better solution to me and the desire to stick
with traditional methods of braking is just that, tradition.

Probably subject to debate, but:

Disks are more expensive.
Discs are more fragile.
Discs place more force on the wheel spokes in order to transfer the
braking force to the rim.
Discs are heavier.
Discs need forks that can cope with the forces applied to them & are
therefore heavier than would otherwise be necessary.

The last few are probably why roadies don't seem to use them -- you
can't use light radial spoked wheels with discs IIRC.

Everything has tradeoffs: Discs brakes are a great piece of
technology, but not without at least some drawbacks.

Phil

--
http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt

Phil Armstrong wrote on 23/06/2006 22:42 +0100:

Quoted message said:

Discs are more fragile.

I've been running discs on my mountain bike for six years now and I've
not touched them apart from replacing pads. Hardly fragile. I spent
much more time fettling rim brakes.

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

in message <[email hidden]>, Chris Eilbeck

(') said:

Simon Brooke said:

in message <[email hidden]>, Brendan Halpin

(') said:

druidh <[email hidden]> writes:

> Brendan Halpin wrote:
>> but the wet-weather stopping power is far less
>> than I would like.
>>
>> What options have I to improve the performance?

> They're called disks. Have a look around, you'll see loads.

As far as I can tell, no one sells disc brakes with levers for drop
bars.

They do. But the idea that disk brakes have more stopping power than
well adjusted rim brakes is just false.

Disks must have some advantages over rim brakes. The one I can see
would be that

- your pads are pressing flat against a disk and compressing it rather
than pressing on the sides of a u-section rim.

- you have separate mechanical system for supporting the rider (the
wheel rim) and the braking system, which will have different and
probably competing design goals.

- you can run disks hotter, no need to keep them cool because you've
got a a tyre in contact with the braking surface.

All those things are true. And the downside is

* they're heavier;
* the front wheel has to be able to transmit torque, so you can't have
radial spoking;
* the wheels are weaker, because the flanges are closer together so that
the angle of the spokes is narrower.

The second one there is mainly cosmetic, but the first is significant and
the third is /very/ significant.

Quoted message said:

Disks just seem like a better solution to me

They do. Until you start to think about it.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
Windows 95:
You, you, you! You make a grown man cry...
M. Jagger/K. Richards

in message <[email hidden]>, Marz

(') said:

Phil Armstrong said:

Marz said:

It's not my idea, it's fact. While one can unweight a bike to lift
it over roots or potholes, one can also weight the bike for
cornering and braking. It's akin to 'twisting' the bar grips back to
gain real wheel grip on steep climbs. You can try it yourself, pull
a short skid on dirt or tarmac using just enough power to lock the
rear wheel (or both if on dirt). Now try it again, but this time
attempt to 'jump' on the pedals during the skid, you'll increase
traction to the wheel and unlock it and maybe stop sooner.

As has been pointed out elsewhere in this thread, the limit of braking
is when the torque on the rider + bike due to the rider pushing
against the bars against the braking of the bike is just short that
required to lift the back wheel. Any more braking force will tip the
rider over the bars.

You shouldn't be pushing against the bars, the bars are for steering,
braking and shifting gear, most (98.7657%(yes I made it up)) of your
weight should be on your pedals.

If you don't push against the bars when braking, you /will/ go over them.
Try it some time - it's the classic beginners' crash.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Diplomacy, American: see Intelligence, Military

in message
<[email hidden]>, Mike

Causer (') said:

Tony Raven said:

That's the hard work way to do it, lifting the bike up physically.
The easy way is to move your weight back to lift the front wheel and
then push forwards on the bars to bring the back wheel up.

Ah yes. Yogic Flying for bicycles.

Was that you or the International Space Station I saw wizzing by last
night ;-)

Don't laugh. Most of my friends can do it. It makes me sick.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Morning had broken, and we had run out of gas for the welding torch.

Simon Brooke said:

All those things are true. And the downside is

* they're heavier;

That I can accept, and would accept for better performance.

Quoted message said:

* the front wheel has to be able to transmit torque, so you can't
have radial spoking;

What is this thing for radial spoking?

Quoted message said:

* the wheels are weaker, because the flanges are closer together so
that the angle of the spokes is narrower.

That I can see.

Quoted message said:

The second one there is mainly cosmetic, but the first is
significant and the third is /very/ significant.

Quoted message said:

Disks just seem like a better solution to me

They do. Until you start to think about it.

So it's just a fashion thing? Why does no-one outside cycling stay
with rim or drum brakes?

Chris
--
Chris Eilbeck

"Brendan Halpin" <[email hidden]> wrote

Quoted message said:

Yesterday it rained on my commute -- strange to say it but it
hadn't rained here for weeks -- and it struck me forcibly how [censored]
my brakes are in the wet. Koolstop salmon pads, cantilever brakes,
all in good order, but the wet-weather stopping power is far less
than I would like.

I have two pairs of part used salmons in my box of bits. They worked when
new but went off badly. On my commute I reach nearly 30mph before having to
stop at a junction and I expect to take well under 5 seconds about it.
Intolerable. They shrieked like a banshee too.

In article said:

Tony Raven said:

That's the hard work way to do it, lifting the bike up physically. The
easy way is to move your weight back to lift the front wheel and then push
forwards on the bars to bring the back wheel up.

Ah yes. Yogic Flying for bicycles.

As I read it, Tony actually means "bring the back wheel up and the front
back down", which (AIUI) isn't actually a bunny hop but does do the job
of getting both wheels over an obstacle with less work.
Though I have seen BMX cyclists and skateboarders do things that _look_
very much as if they defy the laws of physics. Maybe Yogic Flying really
is the answer.

in message <[email hidden]>, Chris Eilbeck

(') said:

Simon Brooke said:

All those things are true. And the downside is

* they're heavier;

That I can accept, and would accept for better performance.

Quoted message said:

* the front wheel has to be able to transmit torque, so you can't
have radial spoking;

What is this thing for radial spoking?

It produces a stiff, light wheel. Not /much/ stiffer or /much/ lighter,
of course.

Quoted message said:

Quoted message said:

* the wheels are weaker, because the flanges are closer together so
that the angle of the spokes is narrower.

That I can see.

That's pretty significant. Nine and ten speed cassettes take a lot out of
the effective width of the hub in any case. When you add a disk as well,
you end up with wheels a lot weaker than they were thirty years ago.
That's /progress/?

Quoted message said:

Quoted message said:

The second one there is mainly cosmetic, but the first is
significant and the third is /very/ significant.

Quoted message said:

Disks just seem like a better solution to me

They do. Until you start to think about it.

So it's just a fashion thing? Why does no-one outside cycling stay
with rim or drum brakes?

Because people outside cycling have very different technical
requirements.

Disk brakes are legal, under the rules, for bikes used in UCI road
racing, including, e.g., the Tour de France. Why do you think /none/ of
the teams have chosen to adopt them?

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; Drivers in the UK kill more people every single year than
;; Al Qaeda have ever killed worldwide in any single year.

Simon Brooke said:

That's pretty significant. Nine and ten speed cassettes take a lot out of
the effective width of the hub in any case. When you add a disk as well,
you end up with wheels a lot weaker than they were thirty years ago.
That's /progress/?

Aha! another argument in favour of hub gears, stronger wheels. Go on,
you know it makes sense.

--
Don Whybrow

Sequi Bonum Non Time

Are you still here? The message is over. Shoo! Go away!

In article <[email hidden]>

Phil Armstrong said:

Marz said:

Phil Armstrong said:

As has been pointed out elsewhere in this thread, the limit of braking
is when the torque on the rider + bike due to the rider pushing
against the bars against the braking of the bike is just short that
required to lift the back wheel. Any more braking force will tip the
rider over the bars.

You shouldn't be pushing against the bars, the bars are for steering,
braking and shifting gear, most (98.7657%(yes I made it up)) of your
weight should be on your pedals.

Basic physics again: if you're at the limit, you have to be pushing
against the bars. Unless you can get your COG lower than the axle of
the front wheel then you have to have something to push against to
stop yourself going over the bars!

Actually it's not the axle that matters, it's the tyre contact patch -
so unless you can get your centre of mass lower than the road it's still
theoretically possible to launch yourself. However, until tyre
technology can come up with the sort of grip required, LWB recumbent
riders needn't worry too much about it. :-)

Rob Morley said:

In article <[email hidden]>

Phil Armstrong said:

Marz said:

Phil Armstrong wrote:
> As has been pointed out elsewhere in this thread, the limit of braking
> is when the torque on the rider + bike due to the rider pushing
> against the bars against the braking of the bike is just short that
> required to lift the back wheel. Any more braking force will tip the
> rider over the bars.

You shouldn't be pushing against the bars, the bars are for steering,
braking and shifting gear, most (98.7657%(yes I made it up)) of your
weight should be on your pedals.

Basic physics again: if you're at the limit, you have to be pushing
against the bars. Unless you can get your COG lower than the axle of
the front wheel then you have to have something to push against to
stop yourself going over the bars!

Quoted message said:

Actually it's not the axle that matters, it's the tyre contact patch -
so unless you can get your centre of mass lower than the road it's still
theoretically possible to launch yourself. However, until tyre
technology can come up with the sort of grip required, LWB recumbent
riders needn't worry too much about it. :-)

A coefficient of friction of 1, which looks so frequently like a
maximum friction that some folk have assumed that it must be a
theoretical maximum limit, corresponds to an angle of 45 degrees
between front tyre contact patch and combined centre of gravity of
bike and rider, i.e. with that coeff of friction and angle, your back
wheel is just lifting off the ground at the same time as your front
wheel is starting to skid.

A coefficient of friction of 1 is often found between dry roads and
tyres. A good dry road and racing tyres can get up to 1.3ish.

If you look at photographs of folk on bikes and estimate angle between
CofG and front wheel contact patch you will appreciate why you can't
brake upright bikes nearly as fast as cars or motorcycles. At least
they're a big improvement over the penny farthing :-)

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

Phil Armstrong wrote:
[snip]

Quoted message said:

Disks are more expensive.
Discs are more fragile.
Discs place more force on the wheel spokes in order to transfer the
braking force to the rim.
Discs are heavier.
Discs need forks that can cope with the forces applied to them & are
therefore heavier than would otherwise be necessary.

You forgot the one about discs making your whells fall off if the
skewers aren't tight enough

<runs for cover>

TL

Chris Malcolm said:

Rob Morley said:

In article <[email hidden]>

Phil Armstrong said:

Marz <[email hidden]> wrote:
> Phil Armstrong wrote:
>> As has been pointed out elsewhere in this thread, the limit of braking
>> is when the torque on the rider + bike due to the rider pushing
>> against the bars against the braking of the bike is just short that
>> required to lift the back wheel. Any more braking force will tip the
>> rider over the bars.
>
> You shouldn't be pushing against the bars, the bars are for steering,
> braking and shifting gear, most (98.7657%(yes I made it up)) of your
> weight should be on your pedals.

Basic physics again: if you're at the limit, you have to be pushing
against the bars. Unless you can get your COG lower than the axle of
the front wheel then you have to have something to push against to
stop yourself going over the bars!

Quoted message said:

Actually it's not the axle that matters, it's the tyre contact patch -
so unless you can get your centre of mass lower than the road it's still
theoretically possible to launch yourself. However, until tyre
technology can come up with the sort of grip required, LWB recumbent
riders needn't worry too much about it. :-)

A coefficient of friction of 1, which looks so frequently like a
maximum friction that some folk have assumed that it must be a
theoretical maximum limit, corresponds to an angle of 45 degrees
between front tyre contact patch and combined centre of gravity of
bike and rider, i.e. with that coeff of friction and angle, your back
wheel is just lifting off the ground at the same time as your front
wheel is starting to skid.

A coefficient of friction of 1 is often found between dry roads and
tyres. A good dry road and racing tyres can get up to 1.3ish.

If you look at photographs of folk on bikes and estimate angle between
CofG and front wheel contact patch you will appreciate why you can't
brake upright bikes nearly as fast as cars or motorcycles. At least
they're a big improvement over the penny farthing :-)

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

Warning; no science here.

It's funny you mention angles as I was trying out a few different body
positions to see if I could get better performance from my brakes and
qualify any of the BS I came up with last week.

Two (three) things I found out were

1, you can brake heavily without pushing on the bars by pushing back
through the pedals, but this has the adverse affect of

2, reducing critical weight on the front wheel allowing the front wheel
to skip/skid.(this happened on tarmac and dirt)

3, If you put your weight too far back the front brake become useless
and you have to use the back brake to stop before you hit a small cliff
face. (MTB on loose dirt)

So I found that pushing back on the bars AND pedals, while I brake, at
around 45 degrees adds some traction to both wheels and I stop/slow
down quicker. Plus the additional rear ward weight of my [censored] helps
counter act the compression on the front fork and it stays more active
while braking.

I guess it's something my body already knew, as it's I've ridden for
years, but I'd never stopped to think about it.

Laters,

Marz

The Luggage said:

Phil Armstrong wrote:
[snip]

Quoted message said:

Disks are more expensive.
Discs are more fragile.
Discs place more force on the wheel spokes in order to transfer the
braking force to the rim.
Discs are heavier.
Discs need forks that can cope with the forces applied to them & are
therefore heavier than would otherwise be necessary.

You forgot the one about discs making your whells fall off if the
skewers aren't tight enough

<runs for cover>

Oh yeah, that too 🙂

Phil

--
http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt