Disk Brakes vs. V Brakes??

Yes and no. Depends on the brake type, as well as the setup. If the people
with the tandem have a caliper/rotor disc brake, they'd find improved
performance by going to a larger rotor.

" wrote in message
oups.com...
jim beam wrote:
wrote:
Hi,

- After playing with the brakes for a few minutes, I noticed that the
discs get noticeably warm, around 170F. Are there ever heating issues
with disc brakes on longer downhill segments? Seems a stupid question,
but they did get quite warm just by playing around on level ground for
about ten minutes.

they get warm because of the friction - that's what all brakes do.
you'll have no problem with heating issues on a disk braked bike - once
set up correctly, use with complete confidence.


Regarding the heating issue, I came across a couple on a tandem who had
a hydraulic disk brake in back, instead of a drag brake. They said
that on long downhills the brake heating transfers heat to the fluid,
the fluid expands and they end up with the brake applied without any
lever action. They have to stop and let the fluid cool.

A tandem drag brake and a downhill ATB are not the exact same situation
but both can expect to sometimes apply the brake for 20-30 minutes on a
very long downhill. Does this ever occur on an ATB?

Tom

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Per :
A tandem drag brake and a downhill ATB are not the exact same situation
but both can expect to sometimes apply the brake for 20-30 minutes on a
very long downhill. Does this ever occur on an ATB?

I've had my front brake (Hope C2) lock up in that manner when descending a very
steep hill.

Somebody who knows can chime in, but my suspicion is that phenom is limited to
closed-system hydraulic brakes.

I also think it's aggravated by having fluid that needs changing bc after I bled
the brake, it stopped happening.
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In article
. com,
"Marz" wrote:

Here's a question, which action produces the most heat, keeping the
brakes on to control speed on a steep hill or letting the bike go and
then jamming on the brakes at the last second to kill the speed?
Laters,

Depends. If it is a fast road descent, you brake very
hard for a short time, then run up to speed again
whereupon the air flow cools the rim before much heat
gets to the tire. On a long slow descent, road or
trail, nothing works. You need to stop and let the
system cool.

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Marz wrote:
wrote:
jim beam wrote:
wrote:
Hi,

- After playing with the brakes for a few minutes, I noticed that the
discs get noticeably warm, around 170F. Are there ever heating issues
with disc brakes on longer downhill segments? Seems a stupid question,
but they did get quite warm just by playing around on level ground for
about ten minutes.

they get warm because of the friction - that's what all brakes do.
you'll have no problem with heating issues on a disk braked bike - once
set up correctly, use with complete confidence.


Regarding the heating issue, I came across a couple on a tandem who had
a hydraulic disk brake in back, instead of a drag brake. They said
that on long downhills the brake heating transfers heat to the fluid,
the fluid expands and they end up with the brake applied without any
lever action. They have to stop and let the fluid cool.

A tandem drag brake and a downhill ATB are not the exact same situation
but both can expect to sometimes apply the brake for 20-30 minutes on a
very long downhill. Does this ever occur on an ATB?


I've never had heat cause the brakes to apply through heat expansion.
What I do experience is dot4 brake fluid boiling (or the water in the
fluid boiling) and I loose all braking power. And I have to wait until
it cools before continuing down hill. On the same hill with v-brakes I
had a front tire blow because the rim got too hot.

My make of disk brake is not compatible with dot5 fluid, which if I
could use it, would help.

Here's a question, which action produces the most heat, keeping the
brakes on to control speed on a steep hill or letting the bike go and
then jamming on the brakes at the last second to kill the speed?
Laters,

Marz

--
There is a higher temp grade of DOT fluid called DOT 5.1. Despite it's numerical designation, it IS NOT the same as DOT 5 fluid, it's a grade of DOT 4 developed specifically for high temp braking (wonder why they didn't call it 4.1?). Some of the motorcycle road racing teams are using it. Speaking of brake fluid, when I worked in a motorcycle shop, this was the second most neglected item of maintenance (changing the fluid). The most neglected was checking tire pressure.

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I'm not surprised. Tandems have double the weight and therefore double
the energy to be dissipated while braking.

It will be more than double - significantly more as the double weight
going downhill only experiences the air resistance of a single rider.
As any rider knows from experience, the heavier rider will descent
faster (handling aside) than a lighter rider.

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On Wed, 11 Oct 2006 00:58:40 -0600, jlee wrote:

I'm not surprised. Tandems have double the weight and therefore double
the energy to be dissipated while braking.

It will be more than double - significantly more as the double weight
going downhill only experiences the air resistance of a single rider.

This is true.

Matt O.

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a écrit :

Hi,

I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
for the first time, and would appreciate your input on my impressions:

- On the first bike I tried, it was not possible to block the wheel
with the disk brake. I checked and found that the disk was oily. On
another bike (same brake) I was able to get the wheel to block, but
with application of extreme force to the brake handle, MUCH more than
required by any V brake I ever tried.

Question: Are Hydraulic Brakes really weaker than V brakes, or was this
bike just assembled by monkeys?

- I noticed that the hydraulic disc brakes have a much 'spongier' feel
than the cable actuated V brakes. This I guess was related to the
hydraulic hose / brake line expanding under pressure, because it was ok
on the front brake (1/2 of the brake lever way until full braking), and
not acceptable no the rear brake (had to pull the brake lever almost up
to the handle bar to get full breaking power)

Question: Is this again a problem of monkey assembly (not enough
fluid?, air in the lines?, what else? ...), or cheap brake lines, or
both? And are there better brake lines that expand less than the stock
ones?
Or ARE hydraulic disc brakes just spongier? If yes, that much
spongier??

- After playing with the brakes for a few minutes, I noticed that the
discs get noticeably warm, around 170F. Are there ever heating issues
with disc brakes on longer downhill segments? Seems a stupid question,
but they did get quite warm just by playing around on level ground for
about ten minutes.

Thanks a lot!

PS: All the monkey references are founded on an employee there telling
me that 'there are no electrical brakes' when I asked for differences
between hydraulic and cable actuated. When I asked her that about the
front fork maxing out, i.e. hitting the limit of it's travel hard, she
replied with 'many people like their forks soft'. (I found out how they
can be adjusted later.) When I showed her that the (later found to be
well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
So monkeys or Neanderthals are definitely a possibility in that store.
But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I

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the model that you use?


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On Tue, 10 Oct 2006 00:04:56 CST, wrote:


Hi,

I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
for the first time, and would appreciate your input on my impressions:

- On the first bike I tried, it was not possible to block the wheel
with the disk brake. I checked and found that the disk was oily.

Well, that would explain it. BTW, a brake which locks the front wheel
when the bike is actually being ridden can be an unpleasant thing to
have. If you get one, I suspect that you will discover this at some
point.

On
another bike (same brake) I was able to get the wheel to block, but
with application of extreme force to the brake handle, MUCH more than
required by any V brake I ever tried.

Question: Are Hydraulic Brakes really weaker than V brakes, or was this
bike just assembled by monkeys?

In my experience, most v-brakes require far less finger pressure to
produce a given amount of stopping power than a disc brake.

- I noticed that the hydraulic disc brakes have a much 'spongier' feel
than the cable actuated V brakes. This I guess was related to the
hydraulic hose / brake line expanding under pressure, because it was ok
on the front brake (1/2 of the brake lever way until full braking), and
not acceptable no the rear brake (had to pull the brake lever almost up
to the handle bar to get full breaking power)

Cable-operated disc brakes often have similar results. This is not
unusual for disc brakes as a class of unit, but results vary wildly
between setups; it is foolish to infer anything about a specific
brake's probable operating characteristics on the basis of other
brands or models. The only way to reliably establish what a given
brake does is to try it and see.

Question: Is this again a problem of monkey assembly (not enough
fluid?, air in the lines?, what else? ...), or cheap brake lines, or
both? And are there better brake lines that expand less than the stock
ones?

To each: Possibly.

Or ARE hydraulic disc brakes just spongier? If yes, that much
spongier??

Any brake can be made to work poorly. Some can't be made to work
well. Each must be evaluated on its own merits.

- After playing with the brakes for a few minutes, I noticed that the
discs get noticeably warm, around 170F.

Gosh, you had a contact thermometer available? I'm impressed.

Are there ever heating issues
with disc brakes on longer downhill segments? Seems a stupid question,
but they did get quite warm just by playing around on level ground for
about ten minutes.

Yes, it is possible to get disc brakes hot enough on a long descent
(especially with a heavy rider or on a steep grade) to discolor the
disc. Whether this is a problem depends on other factors that vary
from brake to brake.

PS: All the monkey references are founded on an employee there telling
me that 'there are no electrical brakes' when I asked for differences
between hydraulic and cable actuated.

Correct: there are no electric brakes. If you used the term "cable
actuated" they should have known you were talking about something that
was not electrically operated, how did you manage to get them to think
that an electrical connection was involved?

When I asked her that about the
front fork maxing out, i.e. hitting the limit of it's travel hard, she
replied with 'many people like their forks soft'. (I found out how they
can be adjusted later.)

What does this have to do with brakes?

When I showed her that the (later found to be
well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'

Oil contamination of disc brakes has been an issue with motorcycles as
well, for much longer. It happens. When the pads get oiled, you
generally have to replace them; if they're getting oiled by a leaking
fork, then you need a better fork. In the case of bicycles, the best
solution is often to go back to V-brakes, but not always.

So monkeys or Neanderthals are definitely a possibility in that store.
But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I

I think I'd shop for something else.
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Werehatrack wrote:
On Tue, 10 Oct 2006 00:04:56 CST, wrote:


snip

- After playing with the brakes for a few minutes, I noticed that the
discs get noticeably warm, around 170F.


Gosh, you had a contact thermometer available? I'm impressed.

IR Thermometer. Every cyclist should have one.

http://www.webbikeworld.com/r2/digit...hermometer.htm

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On Thu, 12 Oct 2006 11:51:03 CST, Tosspot
wrote:

Werehatrack wrote:
On Tue, 10 Oct 2006 00:04:56 CST, wrote:


snip

- After playing with the brakes for a few minutes, I noticed that the
discs get noticeably warm, around 170F.


Gosh, you had a contact thermometer available? I'm impressed.

IR Thermometer. Every cyclist should have one.

http://www.webbikeworld.com/r2/digit...hermometer.htm

I'll admit that I'm dying to get one, but I really can't figure out
what I'd use it for. I guess it would be cool to have one when someone
asks if they have a temperature. Instead of the old tried and true
hand to the forehead, you can just zap them right between the eyes -
non-laser version probably better for this application.

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