Pros and cons of mechanical vs hydraulic disc brakes?

Paul Boyd wrote on 16/02/2007 09:02 +0100:

Dunno, but over on (USA biased) alt.mountain-bike they've been talking
about forks locking up with the cold, plastic bits snapping with the
cold, but no-one's mentioned brakes not working. Maybe those whose
brakes failed in the cold were unable to report that fact :-)


What I have had in the cold is rims glazing with ice removing all
braking capability. Disks seem to be much less prone, presumably
because they both run hotter and are not being immersed and cooled in
puddles.

--
Tony

"...has many omissions and contains much that is apocryphal, or at least
wildly inaccurate..."
Douglas Adams; The Hitchhiker's Guide to the Galaxy

Tony Raven wrote:

Clive George wrote on 16/02/2007 02:35 +0100:

Disk brakes may have less surface to dump the heat to the atmosphere,
but they can safely run at a higher temperature than a rim (I've
demonstrated this in the past...), and this means they can dump heat
quite well.


I know people with disks that have been blued by the temperature after a
long steep technical descent. The brakes still worked and work fine. I
also know people who have had tyres blown by the rim temperature doing
the same with rim brakes.

and the whole if the rim gets knocked slightly out of true the brakes go
from good to rather poor.

where disks remain the same.

roger

"Duncan Smith" a écrit:

So, the bike came with some sleek carbon forks which only
allowed up to 28mm width tyres. Cycling to work on un-gritted
icy back roads made me a little twitchy, so I let the LBS fit some
cross forks and either canties or a v-brake - they went for Vee
in the end - Shimano Deore. I did mention about the 287V, but
they thought that the front cable was short enough that it wasn't
necessary - and kind of isn't, at least for one of my wheels. The
other wheel has a slight, slight buckle that means I just have to
slacken of the v-brake a little, but the result is that by the time I
pull the lever (standard road lever) so that the pads bite the rims,
there isn't all that much free travel left before touching the bars,
which in the wet is definitely sub-par.

As you've discovered, you really need more cable pull to work a V-brake. The
287V will do that, and there are a few other options, like the "travel
agent" Rob Morley mentioned:

http://www.phred.org/~alex/bikes/brakes.html

I've run a time-trial style bar-end brake lever with V-brakes in a cowhorn
bar, and that gave enough travel to run a V-brake with more normal rim
clearances. Likewise, a Campag or Tektro style lever with a quick release in
the lever body can be run with the QR open to get more lever travel. That
doesn't solve the inherent leverage mismatch between brake and lever, but it
stops you running out of travel.

Another option would be a centre-pull canti, like the Avid Shorty or Empella
Froggleg. The Avids in particular are easy to adjust, and the cable pull
requirement is compatible with your levers.

The idea was that it would be quick and easy to swap the wheels over
depending upon the weather, one with a 28mm tread, the other a 35mm
studded tyre, but that didn't really work out because the rims are
different widths - and it takes longer to dick with the vees than it
does to change the tyre over.

I ran 287V levers with XT V-brakes on a touring bike that I used with two
sets of wheels: one heavy, one light. It worked fine. The "parallel push"
system of XT and XTR V-brakes mean there's generally no need to adjust the
pads for different rims - you just adjust cable slack with the barrel
adjuster on the noodle supplied with the levers. Takes about two seconds.

Strictly speaking I could probably make do without, but I wouldn't
mind trying out some discs anyway. Never had discs before.

Fair enough. But consider you'll need a new fork, hubs (if your current hubs
aren't disk compatible), rotors, caliper,
lever, and the ensemble will weigh more than a matched lever and rim brake.

James Thomson

Den 2007-02-16 10:02:47 skrev Paul Boyd usenet.dont.work@plusnet:

Ian Smith said the following on 15/02/2007 18:58:

Only thing I've not seen in the discussion to date is that mechanical
are prone to cables frrzing if they get wet in them and it becomes
cold. Presumably hydraulic don't (until it becomes very cold? What's
the freezing point of the fluid?

Dunno, but over on (USA biased) alt.mountain-bike they've been talking
about forks locking up with the cold, plastic bits snapping with the
cold, but no-one's mentioned brakes not working. Maybe those whose
brakes failed in the cold were unable to report that fact :-)


Cable brakes easily stop working overnight if you leave the poor bike out
in the cold. But I've never heard of them stop working while riding. Just
pull them once in a while to prevent ice from forming.

Don't know about hydraulic brakes.

Erik Sandblom
--
Oil is for sissies

Tony Raven wrote:
Clive George wrote on 16/02/2007 02:35 +0100:

Disk brakes may have less surface to dump the heat to the atmosphere,
but they can safely run at a higher temperature than a rim (I've
demonstrated this in the past...), and this means they can dump heat
quite well.

I know people with disks that have been blued by the temperature after a
long steep technical descent. The brakes still worked and work fine. I
also know people who have had tyres blown by the rim temperature doing
the same with rim brakes.

Ditto: I've melted rim brake pads descending, and also got my rims up to
blueing temperature.

One of those brake technologies faded with the heat, and the other didn't.

A

Ambrose Nankivell wrote on 16/02/2007 19:09 +0100:

Ditto: I've melted rim brake pads descending, and also got my rims up to
blueing temperature.


Since steel bluing temperature is 300C I doubt that very much.


--
Tony

"...has many omissions and contains much that is apocryphal, or at least
wildly inaccurate..."
Douglas Adams; The Hitchhiker's Guide to the Galaxy

Tony Raven wrote:
Ambrose Nankivell wrote on 16/02/2007 19:09 +0100:

Ditto: I've melted rim brake pads descending, and also got my rims up
to blueing temperature.


Since steel bluing temperature is 300C I doubt that very much.

Quite rightly so. I meant to write discs.

In article , Simon
Brooke
says...
All brakes work by turning
kinetic energy into heat and then dumping that to the atmosphere. Disk
brakes have less surface to do this with.

But run at a higher temperature ...

In newsp.tnutmanmzubk0m@toshiba,
Erik Sandblom tweaked the Babbage-Engine to tell us:

Cable brakes easily stop working overnight if you leave the poor bike
out in the cold. But I've never heard of them stop working while
riding. Just pull them once in a while to prevent ice from forming.

A couple of weeks ago my front derailleur cable twice froze up on the way
into work in the morning; once after about 10 km and once after 4. It was
fine on the way home once it had thawed out again.

--
Dave Larrington
http://www.legslarry.beerdrinkers.co.uk
This Unit is a productive Unit.

In article , Dave Larrington
says...
In newsp.tnutmanmzubk0m@toshiba,
Erik Sandblom tweaked the Babbage-Engine to tell us:

Cable brakes easily stop working overnight if you leave the poor bike
out in the cold. But I've never heard of them stop working while
riding. Just pull them once in a while to prevent ice from forming.

A couple of weeks ago my front derailleur cable twice froze up on the way
into work in the morning; once after about 10 km and once after 4. It was
fine on the way home once it had thawed out again.


Maybe you should give it a good squirt of moisture displacer.