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



R

Roger Merriman

Guest
Tony Raven <[email protected]> wrote:

> [email protected] (Roger Merriman) wrote in
> news:1i3v58y.5ykd2y1onief8N%[email protected]:
>
> > Tony Raven <[email protected]> wrote:
> >
> >> [...]

> >
> > indeed, the chances of attaully heating a rim or disk on normal bike
> > seem slim.

>
> Not slim at all on a long descent


okay not something i've ever had a problem with but then the geography
means you don't tend to get long fast descents but short and sharp.

ie it might be over 30% or more in places but you'll reach the bottom
before the heat of the rim starts to be a issue.

>
> > and attaully looking and tamdems they seem to have bog
> > standurd brakes, mostly V brakes with the drum to assist. does also beg
> > the question if heat is a problem then why use the rim with the risks
> > that come with that. but use a disk where if it gets hot it shouldn't
> > cause any problems bar brake fade.
> >
> > does suggest that braking is heat rather than stronger brakes, for the
> > tamdems.
> >

>
> You can use disks but you need them designed for tandem heat loads that
> most of them are not. A disk could not be used with a drum on the rear
> wheel because the drum takes up the disk space - so you are going to need
> a rim brake on the back anyway - unlike singles rear brakes are effective
> on tandems. So that leaves you with just a front disk.


ah righty that kinda makes sence. i guess that disks big enought to
disapate the heat would start to get seriously heavy. as car and
motorbike disks are.

roger
--
www.rogermerriman.com
 
D

David Damerell

Guest
Quoting Roger Merriman <[email protected]>:
>standurd brakes, mostly V brakes with the drum to assist. does also beg
>the question if heat is a problem then why use the rim with the risks
>that come with that. but use a disk where if it gets hot it shouldn't
>cause any problems bar brake fade.


Or the disc warping, the hydraulic fluid boiling, plastic bits catching on
fire... yes, Santana produced all these failure modes in disc brakes.

>does suggest that braking is heat rather than stronger brakes, for the
>tamdems.


Stronger brakes as well. For the same deceleration a tandem brake is
working twice as hard, and a tandem can manage higher decelerations than
any solo.

The real answer is that what people think of as "strong" brakes aren't.
_Any_ sensible design of brake can lift the rear wheel (or skid the front
wheel on a poor surface). For solo bikes there is no difference in brake
strength from one design to another.
--
OPTIONS=name:Kirsty,menustyle:C,female,lit_corridor,standout,time,showexp,hilit
e_pet,catname:Akane,dogname:Ryoga,fruit:eek:konomiyaki,pickup_types:"!$?=/,scores:
5 top/2 around,color,boulder:0,autoquiver,autodig,disclose:yiyayvygyc,pickup_bu
rden:burdened,!cmdassist,msg_window:reversed,!sparkle,horsename:Rumiko,showrace
 
D

David Damerell

Guest
Quoting Roger Merriman <[email protected]>:
>which begs the other question if tamdems have allways or for a reasonble
>time had half decent brakes why did it not filter to mountain bikes?


Because mountain bikes can't actually use any more braking than any other
solo bike.
--
OPTIONS=name:Kirsty,menustyle:C,female,lit_corridor,standout,time,showexp,hilit
e_pet,catname:Akane,dogname:Ryoga,fruit:eek:konomiyaki,pickup_types:"!$?=/,scores:
5 top/2 around,color,boulder:0,autoquiver,autodig,disclose:yiyayvygyc,pickup_bu
rden:burdened,!cmdassist,msg_window:reversed,!sparkle,horsename:Rumiko,showrace
 
R

Roger Merriman

Guest
David Damerell <[email protected]> wrote:

> Quoting Roger Merriman <[email protected]>:
> >standurd brakes, mostly V brakes with the drum to assist. does also beg
> >the question if heat is a problem then why use the rim with the risks
> >that come with that. but use a disk where if it gets hot it shouldn't
> >cause any problems bar brake fade.

>
> Or the disc warping, the hydraulic fluid boiling, plastic bits catching on
> fire... yes, Santana produced all these failure modes in disc brakes.
>

still a disk failing has to be safer than a tire blowing off?

which then begs the question why the standard v brakes with out issue
then?

> >does suggest that braking is heat rather than stronger brakes, for the
> >tamdems.

>
> Stronger brakes as well. For the same deceleration a tandem brake is
> working twice as hard, and a tandem can manage higher decelerations than
> any solo.
>
> The real answer is that what people think of as "strong" brakes aren't.
> _Any_ sensible design of brake can lift the rear wheel (or skid the front
> wheel on a poor surface). For solo bikes there is no difference in brake
> strength from one design to another.


that is not my experance at least given enought, speed and/or gradiant.
the differnce can be quite a lot.

roger
--
www.rogermerriman.com
 
R

Roger Merriman

Guest
David Damerell <[email protected]> wrote:

> Quoting Roger Merriman <[email protected]>:
> >which begs the other question if tamdems have allways or for a reasonble
> >time had half decent brakes why did it not filter to mountain bikes?

>
> Because mountain bikes can't actually use any more braking than any other
> solo bike.


really? funny the jump though various cable rim brakes to hydraulic
disks has been a steady improvement in braking.

roger
--
www.rogermerriman.com
 
T

Tony Raven

Guest
[email protected] (Roger Merriman) wrote in
news:1i3vrac.12wh6fh3la53jN%[email protected]:

> still a disk failing has to be safer than a tire blowing off?
>
> which then begs the question why the standard v brakes with out issue
> then?
>


I've had a front tyre blow explosively (not from heating) on a tandem doing
about 30mph downhill on a fire road. Because a tandem has a long wheelbase
it was relatively easy to bring it to a halt. I would much rather go
through that any time than have the brakes fail at that speed on a slope
for which the only answer would be a painful bale out.

--
Tony

" I would never die for my beliefs because I might be wrong."
Bertrand Russell
 
S

Steve Gravrock

Guest
On 2007-09-03, Roger Merriman <[email protected]> wrote:
> David Damerell <[email protected]> wrote:
>
>> Quoting Roger Merriman <[email protected]>:
>> >which begs the other question if tamdems have allways or for a reasonble
>> >time had half decent brakes why did it not filter to mountain bikes?

>>
>> Because mountain bikes can't actually use any more braking than any other
>> solo bike.

>
> really? funny the jump though various cable rim brakes to hydraulic
> disks has been a steady improvement in braking.


It's been a steady improvement in the mechanical advantage of the brake
system, and thus a drop in how much hand pressure you need to get the
same braking, but the total deceleration you can manage is still limited
by going over the bars rather than by any property of the brakes.

Or, to put it differently, properly set up cantilevers will stop you
just as well on a given slope as hydraulic discs. The difference is in
how sore your hands will be at the bottom.
 
C

CoyoteBoy

Guest
On 3 Sep, 17:30, David Damerell <[email protected]>
wrote:
> Quoting Roger Merriman <[email protected]>:
>
> >which begs the other question if tamdems have allways or for a reasonble
> >time had half decent brakes why did it not filter to mountain bikes?

>
> Because mountain bikes can't actually use any more braking than any other
> solo bike.


True, even a 30ft vertical drop only exerts the same braking force on
the brakes as a 30mph road stop, in fact probably less due to tyre
slippage.
 
P

Paul Boyd

Guest
Steve Gravrock said the following on 03/09/2007 22:20:

> Or, to put it differently, properly set up cantilevers will stop you
> just as well on a given slope as hydraulic discs. The difference is in
> how sore your hands will be at the bottom.


The difference is that you might not always want to stop on a given
slope, but have delicate control going down it. Less likely on a
tandem, but on an MTB pointing down a 60 degree loose slope you need
very precise braking control :)

--
Paul Boyd
http://www.paul-boyd.co.uk/
 
P

Peter Clinch

Guest
David Damerell wrote:

> Conversely, most PC joysticks are big chunky things - and, guess what,
> it's easier to fine tune adjustment when "hard over" isn't a centimetre
> away from "dead centre" and you can't do "hard over" just by flicking it.


You seem to have mistaken travel for force required.

> So what's better about fingertips versus a gentle pull with the fingers?


"Fingertips" *is* a nice gentle pull with your fingers. Try that on a
setup like Clive's where the cables haven't been touched for a decade on
mechanicals and all you'll get with a gentle pull with the fingers on a
worryingly accelerating tandem is panic-stricken...

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
Tony Raven <[email protected]> wrote:

> [email protected] (Roger Merriman) wrote in
> news:1i3vrac.12wh6fh3la53jN%[email protected]:
>
> > still a disk failing has to be safer than a tire blowing off?
> >
> > which then begs the question why the standard v brakes with out issue
> > then?
> >

>
> I've had a front tyre blow explosively (not from heating) on a tandem doing
> about 30mph downhill on a fire road. Because a tandem has a long wheelbase
> it was relatively easy to bring it to a halt. I would much rather go
> through that any time than have the brakes fail at that speed on a slope
> for which the only answer would be a painful bale out.


i'm suprised you didn't have more problems but then i guess the extra
stablity of a tamdem helps.

roger
--
www.rogermerriman.com
 
T

Tony Raven

Guest
Paul Boyd <[email protected]> wrote in
news:[email protected]:
>
> Less likely on a
> tandem, but on an MTB pointing down a 60 degree loose slope you need
> very precise braking control :)
>


<pedant>

You can't have a 60 degree loose slope - its beyond the maximum angle of
repose for loose material.

</pedant>


--
Tony

" I would never die for my beliefs because I might be wrong."
Bertrand Russell
 
A

Alan Braggins

Guest
In article <[email protected]>, Tony Raven wrote:
>Paul Boyd <[email protected]> wrote in
>news:[email protected]:
>>
>> Less likely on a
>> tandem, but on an MTB pointing down a 60 degree loose slope you need
>> very precise braking control :)

>
><pedant>
>You can't have a 60 degree loose slope - its beyond the maximum angle of
>repose for loose material.
></pedant>


I think you might reasonably consider damp sand to be a loose slope for
the purpose of riding a bike down it, even though it obviously isn't as
loose as dry sand (which is why it has a much higher angle of repose).
 
R

Roger Merriman

Guest
Steve Gravrock <[email protected]> wrote:

> On 2007-09-03, Roger Merriman <[email protected]> wrote:
> > David Damerell <[email protected]> wrote:
> >
> >> Quoting Roger Merriman <[email protected]>:
> >> >which begs the other question if tamdems have allways or for a reasonble
> >> >time had half decent brakes why did it not filter to mountain bikes?
> >>
> >> Because mountain bikes can't actually use any more braking than any other
> >> solo bike.

> >
> > really? funny the jump though various cable rim brakes to hydraulic
> > disks has been a steady improvement in braking.

>
> It's been a steady improvement in the mechanical advantage of the brake
> system, and thus a drop in how much hand pressure you need to get the
> same braking, but the total deceleration you can manage is still limited
> by going over the bars rather than by any property of the brakes.
>

that as maybe certinaly at slower speeds, but ramp the speed up to and
disks do seem to stop one faster and cleaner then rim brakes, the rim
did stop the bike and safely, but at higher speeds they don't at least
in my experiance attaully stop as fast.

> Or, to put it differently, properly set up cantilevers will stop you
> just as well on a given slope as hydraulic discs. The difference is in
> how sore your hands will be at the bottom.


yes that is one point, that cant's need a harder tug. but also given a
steep enought hill don't stop as well as hydraulic disks. around SW
london and surrrey the hills that are about don't stress the brakes
enought for this to be a issue. get to proper hills and the differnce
becomes very apparent.

roger
--
www.rogermerriman.com
 
C

CoyoteBoy

Guest
On 4 Sep, 13:16, [email protected] (Roger Merriman) wrote:

> that as maybe certinaly at slower speeds, but ramp the speed up to and
> disks do seem to stop one faster and cleaner then rim brakes, the rim
> did stop the bike and safely, but at higher speeds they don't at least
> in my experiance attaully stop as fast.


I suspect this is down to heat buildup - a rim brake has a much higher
contact speed than a disk brake so the pads will suffer from the
effects of heat much faster. Oh and dont forget the rim pads have to
be fairly soft rubbery stuff so as not to eat the soft rims, which
doesnt help with heat dissipation and pad life.
 
P

Peter Clinch

Guest
Steve Gravrock wrote:

> Or, to put it differently, properly set up cantilevers will stop you
> just as well on a given slope as hydraulic discs. The difference is in
> how sore your hands will be at the bottom.


And also in how easy it is to fine tune the braking so you have as much
force as possible /without locking the wheels/. The fine control is
much easier if you're not pulling so hard.

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/
 
B

Ben C

Guest
On 2007-09-04, CoyoteBoy <[email protected]> wrote:
> On 4 Sep, 13:16, [email protected] (Roger Merriman) wrote:
>
>> that as maybe certinaly at slower speeds, but ramp the speed up to and
>> disks do seem to stop one faster and cleaner then rim brakes, the rim
>> did stop the bike and safely, but at higher speeds they don't at least
>> in my experiance attaully stop as fast.

>
> I suspect this is down to heat buildup - a rim brake has a much higher
> contact speed than a disk brake so the pads will suffer from the
> effects of heat much faster.


Yes but the force is lower.

For a given deceleration of a bike weighing a given amount, power
dissipation is the same, whether you're using rims or disks. Sure the
disk is moving slower past the pad but the pad is gripping it tighter.

The amount of heat transferred from the moving bike to the brakes
is the same in both cases.

Heat buildup is rate of kinetic energy dissipation minus what the brakes
can get rid of by cooling. So do disks or rims cool faster? The answer's
not obvious.

> Oh and dont forget the rim pads have to
> be fairly soft rubbery stuff so as not to eat the soft rims, which
> doesnt help with heat dissipation and pad life.


Yes, the pads on disks can possibly work over a wider range of
temperatures from cool (when you first start braking) to very hot. The
disk itself can also be allowed to get hotter since it won't blow the
tyre off the way the rim will.
 
D

David Damerell

Guest
Quoting Roger Merriman <[email protected]>:
>David Damerell <[email protected]> wrote:
>>Or the disc warping, the hydraulic fluid boiling, plastic bits catching on
>>fire... yes, Santana produced all these failure modes in disc brakes.

>still a disk failing has to be safer than a tire blowing off?


Neither is an acceptable outcome.

>which then begs the question why the standard v brakes with out issue
>then?


Please look up "begs the question" to find out what it means.

V-brakes (alone) on a tandem have the difficulty that they will blow off
tyres, so they are not without issue.

>>The real answer is that what people think of as "strong" brakes aren't.
>>_Any_ sensible design of brake can lift the rear wheel (or skid the front
>>wheel on a poor surface). For solo bikes there is no difference in brake
>>strength from one design to another.

>that is not my experance at least given enought, speed and/or gradiant.


If you can't lift the rear wheel, adjust your brakes properly. Note that a
downhill gradient makes this easier, not harder.
--
David Damerell <[email protected]> Kill the tomato!
Today is Second Saturday, August - a weekend.
 
D

David Damerell

Guest
Quoting Roger Merriman <[email protected]>:
>David Damerell <[email protected]> wrote:
>>Because mountain bikes can't actually use any more braking than any other
>>solo bike.

>really? funny the jump though various cable rim brakes to hydraulic
>disks has been a steady improvement in braking.


No, there hasn't. With a well adjusted cable rim brake you can lift the
rear wheel (or skid the front on a poor surface). How can a hydraulic disc
offer more braking than that? It can't.
--
David Damerell <[email protected]> Kill the tomato!
Today is Second Saturday, August - a weekend.
 
M

Marz

Guest
On Sep 4, 3:01 am, Tony Raven <[email protected]> wrote:
> Paul Boyd <[email protected]> wrote innews:[email protected]:
>
>
>
> > Less likely on a
> > tandem, but on an MTB pointing down a 60 degree loose slope you need
> > very precise braking control :)

>
> <pedant>
>
> You can't have a 60 degree loose slope - its beyond the maximum angle of
> repose for loose material.
>
> </pedant>
>
> --
> Tony
>
> " I would never die for my beliefs because I might be wrong."
> Bertrand Russell


You can very easily have a 60 degree slope, rock face, rooty sections,
washed out river banks, but it's not something you're ever going to
attempt to brake on. When things get that steep all you're hoping to
do is roll it out without crashing.