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Can Disk Brakes flip you over the handle bars?



 
 
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  #91  
Old May 4th 08, 01:44 AM posted to rec.bicycles.tech
Nate Nagel[_2_]
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Default car brakes

JG wrote:
My physics-fu is feeling a little weak.

While it is true that the limits on grip strength and size will limit
how much force you can put into the brake pads, it does seem that
that force on the pads at a 28" rim is going to be four times as
effective as pads on a 7" rotor, and that a disk brake will be
inherently less effective than a rim brake. Or am I missing
something?

JG


I'm ASSuming that the disc pucks float much closer to the disc than the
rim brake pads do to the rim, so you can get more mechanical advantage
with the discs without bottoming out the levers.

NB: I know far, far more about car brakes than I do about bicycle discs,
never even having looked closely at one, so I'm just throwing a WAG out
there.

nate

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  #92  
Old May 4th 08, 02:37 AM posted to rec.bicycles.tech
Tom Sherman[_2_]
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Default car brakes

Andre Jute wrote:
[..]
It is good to think about these things. I wonder every time I see a
rear disc brake on a bike what it is *for*.[...]


Mud clearance on an ATB.

Useful braking on a recumbent with rearward weight distribution.

Prevention of rim erosion on any bike ridden in wet weather.

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  #93  
Old May 4th 08, 05:32 AM posted to rec.bicycles.tech
[email protected]
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Default car brakes

On May 3, 8:44 pm, Nate Nagel wrote:

I'm ASSuming that the disc pucks float much closer to the disc than the
rim brake pads do to the rim, so you can get more mechanical advantage
with the discs without bottoming out the levers.


That's true. In fact, the disk brake bikes I've ridden seemed to have
a small, constant amount of scraping of the brake pad against the
disk. I don't know that it slowed me down, since the bikes were
rather slow hybrids, anyway. But the slight noise is something I
wouldn't accept from my caliper brakes.

- Frank Krygowski
  #95  
Old May 4th 08, 06:54 PM posted to rec.bicycles.tech
Ben C
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Default car brakes

On 2008-05-03, Andre Jute wrote:
On May 3, 10:42*pm, JG wrote:
My physics-fu is feeling a little weak.


Braking is limited by the coefficient of friction between the road and
the tire. Theoretically, at least, there is no intrinsic reason for
any of the brake methods (rim, disc, drum) to be inferior to the
others. In practice the mechanics of bikes are so well developed that
any adult or child can apply enough braking force to exceed the
friction between tire and road, regardless of the type of brake
fitted. Under ideal conditions, which is what theory deals in, all
bicycle brakes are better than good enough and therefore equal.


Just being able to lock wheels doesn't mean the brakes are good enough.
They might overheat if you keep them on for a while going down a hill,
or, in a car, brake hard 10 or 20 times between tight corners without
long enough straights in between for them to cool down.

Once they overheat you get brake fade of various kinds as discussed and
on bicycle rim brakes you might get the tyre blowing off.

[...]
It is good to think about these things. I wonder every time I see a
rear disc brake on a bike what it is *for*.


Just to match the front disk brake.
  #96  
Old May 5th 08, 02:38 AM posted to rec.bicycles.tech
Mike
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Posts: 63
Default Can Disk Brakes flip you over the handle bars?

In article , Harry Brogan hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM says...
On Thu, 1 May 2008 11:21:35 -0700 (PDT), landotter
wrote:

On May 1, 12:51 pm, Harry Brogan
hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM wrote:
On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter

wrote:
On Apr 30, 10:49 pm, TBerk wrote:
Obviously I would assume they could if you clamp down fast enough.

Yes, if you don't brace yourself and are unfamiliar with the brake and
grab wildly, any powerful brake can be dangerous--but so can many
things in life. Well adjusted brakes should be easy to modulate,
provided you're not inebriated and have practiced a few panic stops,
and shouldn't necessitate the purchase of a new bicycle.

Be careful when posting questions like this, because you may attract
'bent riders, who are bearded hammers in search of nails--sometimes
with orange flippy flags!

I do NOT have orange flippy flags!


Yellow?



FUNNY!!!!......No....not yellow either.....Here's a photo....

http://i255.photobucket.com/albums/h...1012003_02.jpg

Odd thing is that teh 'recumbent beard' has risen up from the chin to just below the nose...

Mike
  #97  
Old May 6th 08, 07:25 AM posted to rec.bicycles.tech
TBerk
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Posts: 111
Default Can Disk Brakes flip you over the handle bars? - RECAP


This has gotten to be a long thread so let me recap a bit:

- The rim has a 'bubble' bend in it, presumably from a hard hit aginst
a sharp edge, pothole, something.

- I _was_ doing a quick stop manuver on purpouse, but of coure I
hadn't counted on the deformation of the rim which led to an
equivelent 'stick in the rim' action.

- Unrelated to the rim dents, this used bike (found stripped and
abandoned in a field) which I found and rebuilt with what I later
discovered was a set of bent forks. That part is on me to have not
really noticed until the paint began to flake off.

- Hence my interest in new forks which opens up an opportunity to
'upgrade' to a disk brake set up.

Meanwhile we have gotten some thread drift, some 'personalities', and
some actually useful info. Typical Usenet.

The frame itself, (with the rack and seat post with a shock in it),
are pretty decent. Of course the front derailer needs a new shifter;
it's broken (I dislike twist shifters) but over all the thing gets the
job done.

To get a new bike (one I'd feel OK about buying new) means spending
fix'r-up'r car money so I'll give this one another level of rebuild
and save my pennies for now.


Dems me thinks.
TBerk
  #98  
Old May 6th 08, 07:54 AM posted to rec.bicycles.tech
Werehatrack
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Default Can Disk Brakes flip you over the handle bars?

On Wed, 30 Apr 2008 20:49:12 -0700 (PDT), TBerk
may have said:


Obviously I would assume they could if you clamp down fast enough.


Bloody unlikely.

I ask because I bruised some rib bones this week when I stomped the
front brake and *surprise* I found out later my front rim has a bubble
bend in it from (I guess) a pot hole at some recent time.

Made for a portion of the rim that just wasn't going to get past the
brake pads, not while I was trying to actually use said brakes.

It would seem a better setup would be one unaffected by a slightly
bent rim, or so I wonder.


While this is one of the minor advantages of keeping the braking
surface separate from the rim, it's seldom enough of a factor to
justify the added complexity. Good rim brakes at nearly any level
will produce more grab than typical OEM-supplied disc brakes on
low-end and midrange bikes anyway. To toss the rider over the bars,
the wheel must instantaneously cease motion relative to the fork
without breaking traction or bending the fork, which is seldom going
to occur with *any* brake system. I had it happen to me with a stick
jam through the spokes of the front wheel on an ancient
fender-equipped bike decades ago, when I was a lot lighter, but
generally an unexpectedly high braking effort is just going to throw
the rider off the seat and forward against the bars. To go over them,
there needs to be a couple of other factors present.

TBerk
it would have been funny if it hadn't hurt so much at the time


BTDT.

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