# Which Brakes? Avid Mechanical Disc? Magura Big or Marta HydraulicDisc?

R

#### Roger Merriman

##### Guest
David Damerell <[email protected]> wrote:

> Quoting Roger Merriman <[email protected]>:
> >David Damerell <[email protected]> wrote:
> >>Quoting Roger Merriman <[email protected]>:
> >>>David Damerell <[email protected]> wrote:
> >>>>But your perceptions of brake "power" are worthless because every decent
> >>>>design of brake has exactly the same stopping power on a solo.
> >>>maybe in paper,
> >>And in elementary mechanics.

> >i'm sure it terms of heat they are much of a muchness. and yes if you
> >don't move at point X the bike will endo.

>
> And for a given bottom position, every design of brake has the same
> stopping power.

yes but you'll have a job realising that. you will not beable to pull
the levers hard enought.

you can get to the point that the bike will not endo how ever hard you
pull the brakes.
>
> >>>but taking my old cant bike away from the rolling downs
> >>>and to the beacons shows that while it's brakes can cope with the soft
> >>>lumps of the south east. proper hills it lacks the power, compared with
> >>>a newer bike with disks.
> >>Which is still rubbish because an increasing downhill gradient _reduces_
> >>the maximum deceleration.

> >yes if i sit on the saddle and just jank the brake, but most will learn
> >to get out of the saddle and use that weight.

>
> Doesn't matter. If you can brake on the those soft lumps, you can manage
> the deceleration possible on proper hills because it _is less_.
>

no it's perfectly possible to counter. it isn't hard at all.

> >>Which is also still rubbish as anyone can determine with heavy panniers.
> >>30kg in panniers shifts the centre of gravity more than you can by moving
> >>your bottom; and with 30kg in panniers you can still lift the rear wheel
> >>under braking; and a downhill gradient still reduces the maximum
> >>deceleration before that happens.

> >yes of coarse a hill will increase a heavly laden bikes endo point, but
> >you weigh a lot more than 30KG and on some bikes you can move that
> >weight around a lot,

>
> You can move _some_ of that weight around a lot; your arms and legs don't
> move so much for a given bottom shift. And when we say "a lot", it's not a
> lot compared to the distance that rear panniers are below and to the rear
>

on a bike with out rider yes, but a heavily panniered bike will have a
rider when moving, and is likely to be a lot heaver, higher and more
forward, reduceing the benfit of the paniers. with regard to endos

> >>You're just clinging to purely psychosomatic ideas of brake power. It
> >>won't wash; and particularly it won't wash with anyone familiar with
> >>tandem applications, where you actually _can_ produce differences in brake
> >>power.

> >try taking a bike up and down steep hills good 30%

>
> When the gradient gets steep enough, the available braking before endo is
> small regardless of bottom position. That's one reason it's so blindingly
> obvious you're taking rubbish; you're picking the worse case for a brake
> to demonstrate supposedly superior power.

i'm not i'm pointing out that it is possible to counter the endo and
that riding up and down steep hills doesn't not mean that you end up
endoing every time you have to do a emergecy brake.
>
> >shift your weight around by that i don't mean your bottom as you put it

>
> Yes, you do. Your hands won't move; your shoulders won't get any further
> from the handlebars than they are with straight arms, although they will
> drop a bit. Your feet aren't going anywhere. The bottom is exactly the
> part that moves a lot.

on a mountain bike your shoulder will be above and just behind the
handle bars, you can move your shoulder to just above the saddle very
few hills if any would need such a move. your hands and feet stay put
but you can mover your trunk in a ark down and behind. which puts a lot
of weight lower down and rear.

roger
--
www.rogermerriman.com

R

#### Roger Merriman

##### Guest
David Damerell <[email protected]> wrote:

> Quoting Roger Merriman <[email protected]>:
> >David Damerell <[email protected]> wrote:
> >>Quoting Roger Merriman <[email protected]>:
> >>>yes still needs to be some resistance, or it would be too easy to be a
> >>>system that was on/off
> >>Reducing your guesswork to what it is.

> >brakes that can be feathered with out having to use any force proper
> >will be easyer to control, most things requiring fine control try not to
> >require too much effort.

>
> This is just restating the guesswork. Yes, there's a sweet spot or region
> - but you've failed to show that the brakes you personally prefer are in
> it or that other designs are outside it - for all possible rider hand
> strengths.
>

i don't care if the brakes are disks rims, gas, wire fluid, or what
ever.

what i do care about are brakes that will scrub off speed ie 40 to 50
range and allow one to decend with power left.

> >>>look back at your post not the snippage here, you pritty much did if not
> >>>in actualality.
> >>Let's see a quote from you that shows it, then. Hint; you can't.

> >fine

>
> Coo, you're literally minded. But let's see a quote from _me_ that shows I
> said it?
>
> >>This one won't wash with anyone who has made emergency stops downhill
> >>on road. We might not brake as much, but the speeds are higher.

> >if your not saying you lock your wheels at speed then what are you
> >saying?

>
> On a good surface what happens first with the front brake - front lock or
> rear lift?
>

rear lift normally, hence the need to counter.

> >the only limit to how far back and low is rear tire, and saddle more
> >than enought to be more than 30KG of panniers.

>
> No. Atop the rear tyre, the very bottom of the weight you shifted is at
> the top of where panniers would be.
>

no you get a lot further behind than that. at the end of the ark you
will either hit the very edge of the tire.

> >particulally as with 30KG
> >of panniers the possiblt of shifting ones weight much is limited.

>
> Try reading comprehension; it's either/or. The point is, a rider with
> heavy panniers has an overall centre of gravity just as low and rearward
> without shifting his weight.

with paniers you still have yours truely which is much heaver, far
higher, and forward. which more than makes up for the panniers.

>
> >>You can't make a better job of stopping than stopping with the rear wheel
> >>on the edge of lifting.

> >correct which is why you need to shift ones' weight back and push that
> >point to a higher point.

>
>
> >>I certainly think it's partly marketing, but I think the advantages of
> >>discs aren't what you think they are. "Power" is a red herring on solos,

> >considering the weight that a tamdem could be, they really should be
> >useing something a with a lot more bite.

>
> That's sort of the point. There's actually some chance of discovering
> which brakes are powerful.
>

there is differnce between heat and power.
> >>We've had real advantages of hydraulic disc systems listed. Immunity to
> >>wet muddy conditions; low maintenance (especially no rim wear). And, of
> >>course, if a rider has very weak hands they will get a real benefit from
> >>the reduced application force. But "power"? Not a chance.

> >reduced application force is certinaly a real plus in some situations,
> >very few roads are steep enought to be a issue

>
> As I've explained to you several times now, the steeper the road, the
> _less_ the maximum braking.

yes and as i've pointed out you can very effectvly counter that.
>
> >and also mean that one doesn't need to put whole hand on lever when you
> >really should be worring about that rock...

>
> Yes, I worry about rocks with my fingers. Not.

if your trying to navigate a technical section you will want to keep
most of your fingers on the bars for control not brakes.
>
> >>So what? Are you going to put a five-speed gearbox on your bike next?
> >>Just because it fits motorised applications doesn't mean it fits bikes.

> >it works else where and very well. on faster heaver vehicals than a
> >tamdem.

>
> I've no doubt a disc system as heavy-duty as those on a motor car would
> make a fine brake, if you didn't mind it weighing as much as your bike
> did before you fitted it. Of course, it would still be pointless on a solo
> because the limit on a solo still isn't braking "power".

it wouldn't need to be as heavy weight, but bike brakes are light weight
things, look at the disks very thin, there is a middle ground.

roger
--
www.rogermerriman.com

J

#### Jon

##### Guest
"Roger Merriman" <[email protected]> wrote
>
> what i do care about are brakes that will scrub off speed ie 40 to 50
> range and allow one to decend with power left.

Not sure what "decend with power left" means.

But it seems to me that there are perhaps some points of agreement:

1) for braking methods that rely on slowing wheel rotations [1],
there is a maximum obtainable deceleration rate on a bicycle
before the rear will lift and rotate around the front contact
point.

2) changing weight distribution (or bicycle geometry) affects that
maximum deceleration rate.

3) going down a hill implicitly shifts the bike and rider weight
distribution forward.

4) the weight distribution downhill cannot be "further back" than
it would be with the same rider position on flat ground, hence
the maximum possible deceleration rate downhill is lower
than on flat.

5) properly designed and adjusted disk and rim bicycle braking
systems, cable and hydraulic, can produce braking force greater
than the maximum possible deceleration rate.

6) braking power above that required to produce the maximum
deceleration rate is irrelevant for how quickly one may stop.

7) [gratuitous ARBC content] long wheelbase recumbent
bikes certainly have a greater maximum potential
deceleration rate than upright bikes.

This says nothing about which system is nicer, easier to use,
maintain, modulate and control, or resists fading, or is better
suited for wet and muddy conditions, etc... Or which one

There was recently a very good explanation of the limits
of bicycle braking on the phred touring mailing list. Should
be in the archives at:

http://www.phred.org/mailman/listinfo/touring

It was pointed why it's not a good idea to follow cars at
high speeds too closely on a bicycle. Cars can stop at
much higher deceleration rates than bicycles.

Jon Meinecke

[1] alternative braking methods could include dropping an anchor,
deploying a drag parachute, firing retro-rockets, hitting a large
rock face (with or without a tunnel entrance painted on it), etc...

See Wiley Coyote field tests of Acme Products for examples...
%^)

D

#### David Damerell

##### Guest
Quoting Roger Merriman <[email protected].co.uk>:
>David Damerell <[email protected]> wrote:
>>Quoting Roger Merriman <[email protected]>:
>>And for a given bottom position, every design of brake has the same
>>stopping power.

>yes but you'll have a job realising that. you will not beable to pull
>the levers hard enought.

Also rubbish, and a particularly worthless piece of rubbish to produce to
me when you know I ride tandem. Our centre of gravity's far further back
than you can produce with any contortions in the saddle; I can brake
harder than any solo. Hand strength is not the limiting factor.

>on a bike with out rider yes, but a heavily panniered bike will have a
>rider when moving, and is likely to be a lot heaver, higher and more
>forward, reduceing the benfit of the paniers. with regard to endos

Reading comprehension again. The point is, the CoG of "normal rider
position, heavy panniers" is as far back and down as "abnormal rider
position".

>>When the gradient gets steep enough, the available braking before endo is
>>small regardless of bottom position. That's one reason it's so blindingly
>>obvious you're taking rubbish; you're picking the worse case for a brake
>>to demonstrate supposedly superior power.

>i'm not

Yes, you are; the steeper the hill, the less the braking before an endo.
--
David Damerell <[email protected]> Kill the tomato!
Today is Leicesterday, August.

D

#### David Damerell

##### Guest
Quoting Roger Merriman <[email protected]>:
>David Damerell <[email protected]> wrote:
>>>if your not saying you lock your wheels at speed then what are you
>>>saying?

>>On a good surface what happens first with the front brake - front lock or
>>rear lift?

>rear lift normally, hence the need to counter.

So I was not saying you lock the wheels. You _made that up_.

>>Try reading comprehension; it's either/or. The point is, a rider with
>>heavy panniers has an overall centre of gravity just as low and rearward
>>without shifting his weight.

>with paniers you still have yours truely which is much heaver, far
>higher, and forward. which more than makes up for the panniers.

Well, no. Panniers weigh less; they're further from the normal centre of
gravity. Works out about the same.

>>>considering the weight that a tamdem could be, they really should be
>>>useing something a with a lot more bite.

>>That's sort of the point. There's actually some chance of discovering
>>which brakes are powerful.

>there is differnce between heat and power.

Yes, and I'm talking about power. Tandems decelerate twice the load and
can decelerate harder.

>>As I've explained to you several times now, the steeper the road, the
>>_less_ the maximum braking.

>yes and as i've pointed out you can very effectvly counter that.

Well, no, you've babbled aimlessly. A given bottom position can also be
used on a shallower slope; once you do that, on the steeper slope, the
maximum braking is... less.

>>I've no doubt a disc system as heavy-duty as those on a motor car would
>>make a fine brake, if you didn't mind it weighing as much as your bike
>>did before you fitted it. Of course, it would still be pointless on a solo
>>because the limit on a solo still isn't braking "power".

>it wouldn't need to be as heavy weight, but bike brakes are light weight
>things, look at the disks very thin, there is a middle ground.

It would still be pointless for the reason above.
--
David Damerell <[email protected]> Kill the tomato!
Today is Leicesterday, August.

D

#### David Damerell

##### Guest
Quoting Peter Clinch <[email protected]>:
>David Damerell wrote:
>>Somewhere between those two points is a spot or region where it is
>>easiest, but to say that that's a spot not a region and that that spot
>>happens to be the amount of force required by the brakes you have _and_
>>that that will be true for any user is pure guesswork.

>But rather less guesswork if they happen to have considerable experience
>of multiple brake systems.

And of being multiple people, if the guesswork is going to express more
than personal preference.

>How much time have you actually spent using hydraulic brake systems?

I think I'll spare myself the "I have more experience therefore my guess
is correct", thanks.
--
David Damerell <[email protected]> Kill the tomato!
Today is Leicesterday, August.

D

#### David Damerell

##### Guest
Quoting Peter Clinch <[email protected]>:
>David Damerell wrote:
>>But that's a dodge. What you were talking about was performance via not
>>"less maintenance".

>Oh deary me, I have talked about *both* performance being better through
>better feel when maintained and being better in all respects when not
>maintained and left for some time.
>That's two things.

The second of which is then double accounting with "less maintenance".

>>It's the usual confusion - "this
>>_feels_ better so it must _be_ better" (combined with "this feels better
>>_to me_ so it must be better _for everyone_").

>As opposed to "this is what I use and I think it's fine so obviously
>anyone else finding anuthing better is deluded"...

That's a perfectly reasonable thing to say when someone pretends their
personal prefence is universally applicable.

>>As I've just written in another article - too much sensitivity won't work,

>It isn't "too much" that hydraulics give you, it's more than cables, but
>less than too much. A better amount, in other words.

There must be a sweet spot not a region of equal utility because...
--
David Damerell <[email protected]> Kill the tomato!
Today is Leicesterday, August.

P

#### Peter Clinch

##### Guest
David Damerell wrote:

>> How much time have you actually spent using hydraulic brake systems?

>
> I think I'll spare myself the "I have more experience therefore my guess
> is correct", thanks.

That's a nice little sidestep to admitting "practically none at
all, so I'm working almost entirely from theory".

It isn't do I have more, it's do you have much to speak of
whatsoever? If you don't, and I suspect you don't, it's a bit like
Shaun Murray "proving" Alex Moulton hasn't got a clue about
designing road-going suspension based on his "technical mind" and a
trip around the block on an AM, or Nick Maclaren "proving" that
Bromptons are inherently unsafe for tall riders armed with nothing
but a measuring tape.

If I'm wrong about that then an apology is deserved and will be
supplied, but am I?

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 [email protected] http://www.dundee.ac.uk/~pjclinch/

R

#### Roger Merriman

##### Guest
David Damerell <[email protected]> wrote:

> Quoting Roger Merriman <[email protected]>:
> >David Damerell <[email protected]> wrote:
> >>>if your not saying you lock your wheels at speed then what are you
> >>>saying?
> >>On a good surface what happens first with the front brake - front lock or
> >>rear lift?

> >rear lift normally, hence the need to counter.

>
> So I was not saying you lock the wheels. You _made that up_.
>
> >>Try reading comprehension; it's either/or. The point is, a rider with
> >>heavy panniers has an overall centre of gravity just as low and rearward
> >>without shifting his weight.

> >with paniers you still have yours truely which is much heaver, far
> >higher, and forward. which more than makes up for the panniers.

>
> Well, no. Panniers weigh less; they're further from the normal centre of
> gravity. Works out about the same.

can you ladien the paniers so that on the flat with you on the bike, the
bike is at the tipping point? even with the big long hybrid i can make
the front lift by tipping my weight back.
>
> >>>considering the weight that a tamdem could be, they really should be
> >>>useing something a with a lot more bite.
> >>That's sort of the point. There's actually some chance of discovering
> >>which brakes are powerful.

> >there is differnce between heat and power.

>
> Yes, and I'm talking about power. Tandems decelerate twice the load and
> can decelerate harder.
>
> >>As I've explained to you several times now, the steeper the road, the
> >>_less_ the maximum braking.

> >yes and as i've pointed out you can very effectvly counter that.

>
> Well, no, you've babbled aimlessly. A given bottom position can also be
> used on a shallower slope; once you do that, on the steeper slope, the
> maximum braking is... less.
>

it would be a very bad idea to shift one's weight that far as you can
make the bike tip up.

> >>I've no doubt a disc system as heavy-duty as those on a motor car would
> >>make a fine brake, if you didn't mind it weighing as much as your bike
> >>did before you fitted it. Of course, it would still be pointless on a solo
> >>because the limit on a solo still isn't braking "power".

> >it wouldn't need to be as heavy weight, but bike brakes are light weight
> >things, look at the disks very thin, there is a middle ground.

>
> It would still be pointless for the reason above.

roger
--
www.rogermerriman.com

R

#### Roger Merriman

##### Guest
Jon <[email protected]> wrote:

> "Roger Merriman" <[email protected]> wrote
> >
> > what i do care about are brakes that will scrub off speed ie 40 to 50
> > range and allow one to decend with power left.

>
> Not sure what "decend with power left" means.
>

means to decend steep hills as in over 30% at speed with brakes that
will stop rather than just slow.

> But it seems to me that there are perhaps some points of agreement:
>
> 1) for braking methods that rely on slowing wheel rotations [1],
> there is a maximum obtainable deceleration rate on a bicycle
> before the rear will lift and rotate around the front contact
> point.
>
> 2) changing weight distribution (or bicycle geometry) affects that
> maximum deceleration rate.
>
> 3) going down a hill implicitly shifts the bike and rider weight
> distribution forward.
>
> 4) the weight distribution downhill cannot be "further back" than
> it would be with the same rider position on flat ground, hence
> the maximum possible deceleration rate downhill is lower
> than on flat.
>

not entirely get your hanging off the back you can make the bike tip up,
ie endo.

if your used to shifting your weight, you can shift it so the bike will
tip on either end.

> 5) properly designed and adjusted disk and rim bicycle braking
> systems, cable and hydraulic, can produce braking force greater
> than the maximum possible deceleration rate.
>
> 6) braking power above that required to produce the maximum
> deceleration rate is irrelevant for how quickly one may stop.
>
> 7) [gratuitous ARBC content] long wheelbase recumbent
> bikes certainly have a greater maximum potential
> deceleration rate than upright bikes.
>
> This says nothing about which system is nicer, easier to use,
> maintain, modulate and control, or resists fading, or is better
> suited for wet and muddy conditions, etc... Or which one
>
> There was recently a very good explanation of the limits
> of bicycle braking on the phred touring mailing list. Should
> be in the archives at:
>
> http://www.phred.org/mailman/listinfo/touring
>
> It was pointed why it's not a good idea to follow cars at
> high speeds too closely on a bicycle. Cars can stop at
> much higher deceleration rates than bicycles.
>

yes though worth noting they to suffer from weight transfure, even with
sporty set ups the rear's will unweight a fair bit under hard braking.

> Jon Meinecke
>
> [1] alternative braking methods could include dropping an anchor,
> deploying a drag parachute, firing retro-rockets, hitting a large
> rock face (with or without a tunnel entrance painted on it), etc...
>
> See Wiley Coyote field tests of Acme Products for examples...
> %^)

roger
--
www.rogermerriman.com

J

#### Jon

##### Guest
"Roger Merriman" <[email protected]> wrote
> Jon <[email protected]> wrote:
>
>> [ points 1-3]

Great! There seems to be some level of implicit agreement on
most points.

>> 4) the weight distribution downhill cannot be "further back" than
>> it would be with the same rider position on flat ground, hence
>> the maximum possible deceleration rate downhill is lower
>> than on flat.
>>

> not entirely get your hanging off the back you can make the bike tip up,
> ie endo.

Do you mean raising the front wheel by shifting weight back? Obviously
this would dramatically reduce front wheel braking effect! %^)

Equally obviously, this point of "wheelie" moves further back under
deceleration. And the fact that you can move further back on a slope
before the point of front wheel lift illustrates that there's less "room
left
to move" to counter decleration forces on a slope. That is, the point
of equalibrium starts further back on a slope. (For some slopes, there
may be enough "leeway" to correct to deceleration *and* slope, but
at no point can you obtain a greater effective weight shift on a slope
than on the flat. Proof is by simple trigonometry.)

>> [...] Cars can stop at
>> much higher deceleration rates than bicycles.
>>

> yes though worth noting they to suffer from weight transfure, even with
> sporty set ups the rear's will unweight a fair bit under hard braking.

Exactly. And the effect for cars is a tendency for the rear to pass the
front by rotating horizonatally (a sideways endo).

Here's a few excerpts from the posting by someone who seems to
have a lot of practical experience in braking and cites references:

George Hall wrote:

Cars and motorcycles can decelerate at a max rate
...

If you only consider the coefficient of friction of tire
rubber on common pavement surfaces, you would
determine that about 0.7 - 0.8g of braking is possible
for a cyclist.

[for cyclists, a] practical limit of about 0.45 - 0.50g is
all that most folks will achieve before they experience
rear wheel liftoff.

[...] caliper brakes, cantilver brakes, V-brakes, or
disc brakes - all of these in normal circumstances can
produce a deceleration of 0.45g - 0.50g [...]

[...] Of course, there are a lot of other considerations
for your individual circumstances and preferences, I'm
only discussing this from the perspective of braking
ability.

http://search.bikelist.org/getmsg.asp?Filename=touring.10709.0118.eml

So points that disk brakes are better for some conditions, that
they feel better, are more responsive, or are easier to maintain,
or sexier, etc.. may all be good reasons for some to chose them!
Or not sufficient reasons for others... YMMV

Disk brakes do complicate some things, for instance, rear rack

Jon

D

#### David Damerell

##### Guest
Quoting Roger Merriman <[email protected]>:
>David Damerell <[email protected]> wrote:
>>Well, no. Panniers weigh less; they're further from the normal centre of
>>gravity. Works out about the same.

>can you ladien the paniers so that on the flat with you on the bike, the
>bike is at the tipping point?

That's just fore-aft position of centre of gravity; height of centre of
gravity also affects maximum braking.

>>Well, no, you've babbled aimlessly. A given bottom position can also be
>>used on a shallower slope; once you do that, on the steeper slope, the
>>maximum braking is... less.

>it would be a very bad idea to shift one's weight that far as you can
>make the bike tip up.

Not under heavy braking!
--
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D

#### David Damerell

##### Guest
Quoting Peter Clinch <[email protected]>:
>David Damerell wrote:
>>>How much time have you actually spent using hydraulic brake systems?

>>I think I'll spare myself the "I have more experience therefore my guess
>>is correct", thanks.

>That's a nice little sidestep to admitting "practically none at
>all, so I'm working almost entirely from theory".

Well, imagine I do admit that. Let's imagine, not only have I never ridden
a bike with hydraulic discs, I've actually never seen one. When this
thread started, I didn't even know they existed, and I had to go and do a
little reading to find out what they were. In fact, I've only ever used
rod brakes and a little parachute for downhill work.

Let's imagine all that. Would that make your guesswork any less guesswork?
No.
--
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P

#### Peter Clinch

##### Guest
David Damerell wrote:
> Quoting Peter Clinch <[email protected]>:
>> David Damerell wrote:
>>>> How much time have you actually spent using hydraulic brake systems?
>>> I think I'll spare myself the "I have more experience therefore my guess
>>> is correct", thanks.

>> That's a nice little sidestep to admitting "practically none at
>> all, so I'm working almost entirely from theory".

>
> Well, imagine I do admit that. Let's imagine, not only have I never ridden
> a bike with hydraulic discs, I've actually never seen one. When this
> thread started, I didn't even know they existed, and I had to go and do a
> little reading to find out what they were. In fact, I've only ever used
> rod brakes and a little parachute for downhill work.
>
> Let's imagine all that. Would that make your guesswork any less guesswork?
> No.

A while ago you castigated Roger for just not coming out and saying he
out and quantify the experience you have with hydraulic brakes so as to
and what degree of conjecture and theory your comments are based on?

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 [email protected] http://www.dundee.ac.uk/~pjclinch/

R

#### Roger Merriman

##### Guest
David Damerell <[email protected]> wrote:

> Quoting Roger Merriman <[email protected]>:
> >David Damerell <[email protected]> wrote:
> >>Well, no. Panniers weigh less; they're further from the normal centre of
> >>gravity. Works out about the same.

> >can you ladien the paniers so that on the flat with you on the bike, the
> >bike is at the tipping point?

>
> That's just fore-aft position of centre of gravity; height of centre of
> gravity also affects maximum braking.
>

on a bike with out paniers you can get low and rear, such as mountain
bike, you can make a lot of diffenance, you are far and away the
heaviest thing paniers even heavy loaded ones are light in comparison
and have less effect.

i grew up in a steep sided gorge, i'm prefectly aware it's possible to
endo and bike and aware that it's also possible not to, even under hard
braking.

> >>Well, no, you've babbled aimlessly. A given bottom position can also be
> >>used on a shallower slope; once you do that, on the steeper slope, the
> >>maximum braking is... less.

> >it would be a very bad idea to shift one's weight that far as you can
> >make the bike tip up.

>
> Not under heavy braking!

no but it does show that you can move a lot of weight about. down a
steep hill yes you might move a lot but on the flat even under hard
braking it will not be needed as much though some will be needed to
prevent a endo.

roger
--
www.rogermerriman.com

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#### David Damerell

##### Guest
Quoting Peter Clinch <[email protected]c.uk>:
>>>David Damerell wrote:
>>>>I think I'll spare myself the "I have more experience therefore my guess
>>>>is correct", thanks.

>out and quantify the experience you have with hydraulic brakes so as to
>and what degree of conjecture and theory your comments are based on?

I think I've already answered that one, just above. No matter how much or
how little experience I have, your guesswork remains guesswork. I'm sure
you'd love to produce a spurious justification of it on those grounds; too
bad (except inasmuch as you will now say something like "obviously you
don't really have any experience" and use that to justify your pure
guesswork, which will still be nonsense.)
--
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D

#### David Damerell

##### Guest
Quoting Roger Merriman <[email protected]>:
>David Damerell <[email protected]> wrote:
>>Quoting Roger Merriman <[email protected]>:
>>>can you ladien the paniers so that on the flat with you on the bike, the
>>>bike is at the tipping point?

>>That's just fore-aft position of centre of gravity; height of centre of
>>gravity also affects maximum braking.

>on a bike with out paniers you can get low and rear

Maybe you can; but lifting the front wheel doesn't measure "low", just
"rear".

>bike, you can make a lot of diffenance, you are far and away the
>heaviest thing paniers even heavy loaded ones are light in comparison
>and have less effect.

But - as mentioned to you about a million times now - although they are
lighter (but not far and away lighter if heavily laden) - they can be
further from the CoG of the unladen normal-position system.

>>>it would be a very bad idea to shift one's weight that far as you can
>>>make the bike tip up.

>>Not under heavy braking!

>no but it does show that you can move a lot of weight about.

Which is not being disputed. You've lost track of the point in your
semiliterate gibberish.
--
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P

#### Peter Clinch

##### Guest
David Damerell wrote:

What you've done is come up with a precious excuse for not actually
letting on whether you know what you're talking about from
experience or just from theory (guesswork, in other words, even if
educated guesswork).

> No matter how much or
> how little experience I have, your guesswork remains guesswork.

I specifically pointed out I didn't know what experience you
pathetically persist in avoiding giving.

So why not just stop with the precious justifications of not
actually saying whether your opinions are based on experience or
just theory, and let people know? Do you actually want to provide
useful information, or just pour scorn on people?

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 [email protected] http://www.dundee.ac.uk/~pjclinch/

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#### Roger Merriman

##### Guest
Jon <[email protected]> wrote:

> "Roger Merriman" <[email protected]> wrote
> > Jon <[email protected]> wrote:
> >
> >> [ points 1-3]

>
> Great! There seems to be some level of implicit agreement on
> most points.

yup.
>
> >> 4) the weight distribution downhill cannot be "further back" than
> >> it would be with the same rider position on flat ground, hence
> >> the maximum possible deceleration rate downhill is lower
> >> than on flat.
> >>

> > not entirely get your hanging off the back you can make the bike tip up,
> > ie endo.

>
> Do you mean raising the front wheel by shifting weight back? Obviously
> this would dramatically reduce front wheel braking effect! %^)
>

quite the point being that you can achive a fairly radical weight shift.
if needed.

> Equally obviously, this point of "wheelie" moves further back under
> deceleration. And the fact that you can move further back on a slope
> before the point of front wheel lift illustrates that there's less "room
> left
> to move" to counter decleration forces on a slope. That is, the point
> of equalibrium starts further back on a slope. (For some slopes, there
> may be enough "leeway" to correct to deceleration *and* slope, but
> at no point can you obtain a greater effective weight shift on a slope
> than on the flat. Proof is by simple trigonometry.)
>

true, that is less room to move, though in pratice even a very steep
road you can get enought weight to prevent endo. off road some slopes
are steep enought you probably can't but thats a mute point as
attempting to brake would probably be foolish.

> >> [...] Cars can stop at
> >> much higher deceleration rates than bicycles.
> >>

> > yes though worth noting they to suffer from weight transfure, even with
> > sporty set ups the rear's will unweight a fair bit under hard braking.

>
> Exactly. And the effect for cars is a tendency for the rear to pass the
> front by rotating horizonatally (a sideways endo).
>

yes can be done though mostly just a slide forward locking the brakes.

> Here's a few excerpts from the posting by someone who seems to
> have a lot of practical experience in braking and cites references:
>
> George Hall wrote:
>
> Cars and motorcycles can decelerate at a max rate
> of about 0.7 - 0.9g.
> ...
>
> If you only consider the coefficient of friction of tire
> rubber on common pavement surfaces, you would
> determine that about 0.7 - 0.8g of braking is possible
> for a cyclist.
>
> [for cyclists, a] practical limit of about 0.45 - 0.50g is
> all that most folks will achieve before they experience
> rear wheel liftoff.
>
> [...] caliper brakes, cantilver brakes, V-brakes, or
> disc brakes - all of these in normal circumstances can
> produce a deceleration of 0.45g - 0.50g [...]
>
> [...] Of course, there are a lot of other considerations
> for your individual circumstances and preferences, I'm
> only discussing this from the perspective of braking
> ability.
>
> http://search.bikelist.org/getmsg.asp?Filename=touring.10709.0118.eml
>
> So points that disk brakes are better for some conditions, that
> they feel better, are more responsive, or are easier to maintain,
> or sexier, etc.. may all be good reasons for some to chose them!
> Or not sufficient reasons for others... YMMV
>
> Disk brakes do complicate some things, for instance, rear rack
>
> Jon

roger
--
www.rogermerriman.com

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