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Might Dump Road Disc Brakes for Rim Brakes



 
 
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  #1  
Old July 2nd 05, 03:39 AM
mykal
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Default Might Dump Road Disc Brakes for Rim Brakes

The ride: Redline Conquest Disc-R road bike which came equipped with
Avid mechanical road disc brakes, purchased in January 2004.

The experience:
The advantages of disc-brakes for this rider on this bike

Advantages of disc brakes for this rider on this bike:
Quicker brake response when riding in very wet or slushy weather

Disadvantages of disc brakes for this rider on this bike:
Break pad wear consumes about the same amount of dollars per mile
as tire wear.
Chronically warped rotors translate to reduced braking
performance.
Calipers interfere with mounting of fenders. (Panniers not an
issue with this rider.)
Disc brake system adds weight.
Wheel procurement is greatly complicated by parts compatibility
issues.

I've been using this road bike that came with disc brakes since it was
new and now must replace the wheels.

The rear wheel failed early on; it was assessed by two bike shops and
myself as being of a shoddy build after a spoke broke and the rim
warped. In the past, I've had new machine-built wheels re-tensioned
before I put them to use and got many more miles out of them than I
did out of this wheel.

The front wheel was re-tensioned before it started to self-destruct
but I wound up destroying in an accident where I sank it into a deep
pavement crack that brought the bike down from 20+ mph to zero in
about 1/3 of a wheel rotation. (You can tell by where the rim is
crushed.)

Fortunately, the frame is undamaged and rides well. Moreover, the
broken bones suffered are now healed and I've got enough spare coin to
get the bike back up to speed also. With a spare wheel in front, it's
running without the disc for the brake there. With the disc pads worn
to their limits, they've been tossed and to the rear I've swapped in
an R-600 long-reach caliper with Kool Stop salmon pads for performance
testing purposes. I'm impressed at the braking performance of the rim
brake compared to that experienced with discs.

Now that I'm still thinking about a replacement wheel set, I keep
bumping into the quandaries presented by the disc brake setup. It kind
of makes me stuck with a limited selection that actually makes parts
procurement a lot more complicated. I'm remembering how much simpler
life used to be when I had a bike that would simply take any 700C
wheelset.

Installing and adjusting the new rim caliper was easy. Even with the
rear wheel slightly out of true the brake is more than adequate. On
Usenet and other threads people talk about how easy it is to adjust
the disc brake pads, but rarely have I read any mention about the
effort required for adjusting the rotors (See
http://utahmountainbiking.com/fix/diskrtr.htm for specifics.) In my
view, to overlook rotor adjustment when it comes to brake maintenance
is on par with talking about tire inflation when it comes to wheel
building but never mentioning the spokes.

Anyway, I'm thinking about dumping the disc brakes altogether in favor
of long-reach rim brakes and the simplicity of being able to use
standard wheelsets on the bike. My only reservation is over losing
that quick response time provided by disc brakes when riding through a
downpour: I still think, despite all I've learned, that it might be
good to keep a disc in front for that ten or twenty minutes out of the
year when the rim is soaking wet but I might want to stop in a hurry.

Comments?

/* Seattle Mykal */










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  #2  
Old July 2nd 05, 04:24 AM
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Default Might Dump Road Disc Brakes for Rim Brakes



mykal wrote:
...
Anyway, I'm thinking about dumping the disc brakes altogether in favor
of long-reach rim brakes and the simplicity of being able to use
standard wheelsets on the bike. My only reservation is over losing
that quick response time provided by disc brakes when riding through a
downpour: I still think, despite all I've learned, that it might be
good to keep a disc in front for that ten or twenty minutes out of the
year when the rim is soaking wet but I might want to stop in a hurry.

Comments?


It all sounds reasonable to me, except perhaps the last sentence.

I can accept the advantages of disk brakes for muddy conditions that
grind way rims, or for snowy conditions that freeze up the rims and
brakes. But for all the riding I've done in downpours, I can't recall
enough problems to justify switching to disks.

My only real problem occurred back in the early 1970s, with chrome
steel rims with dimples. On a downhill in a downpour I found I had
_zero_ brakes. But once I could afford a better bike with aluminum
rims, wet weather braking was simply slower, not nonexistent. So I
plan ahead.

Panic stops are extremely rare for me anyway. I'd dump the disks.

- Frank Krygowski

  #3  
Old July 2nd 05, 04:44 AM
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Default Might Dump Road Disc Brakes for Rim Brakes

For the wheels, your *rims* are trashed, not your wheels. Buy
replacement rims and lace 'em up (correctly tensioned this time). MUCH
cheaper than buying new wheels.

For the brake rotors - why are you bending rotors? Unless something
hits them - very, very unlikely on the road - they'll stay true
forever. Even on mountain bikes that are regularly crashed and abused,
bending a rotor is extremely rare. Other than replacing them when bent,
there is no "adjustment" required for disk rotors.

And are you really wearing out disk brake pads? Usually they last 2-3
times what a set of rim brake pads do. On the road I'd expect a set to
last many years. I find setting up the Avid brakes extremely finicky
and time consuming - just as bad as normal roadie brakes - but at least
they stay in adjustment for the rest of the year once they're set.

  #4  
Old July 2nd 05, 11:30 PM
mykal
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Default Might Dump Road Disc Brakes for Rim Brakes

sunderland wrote:
For the wheels, your *rims* are trashed, not your wheels. Buy
replacement rims and lace 'em up (correctly tensioned this time).

MUCH
cheaper than buying new wheels.


Yes, re-using the old hubs would mean I don't have to buy new hubs,
and I thank you for the prompt to look into the cost savings. You
might be surprised, but I found the price savings were not that much:

1) The old hubs are still good and can, in fact, be used with a set of
new rims (Velocity Deep-V) and new spokes (Sapim Race) that can be
purchased for $185. Add in the labor costs (for me or for the LBS) and
new wheels that use the old hubs will cost around $245.

2) The old hubs are 28H and I've been leaning toward wheels that have
a higher spoke count. Moreover, new wheels that are competently
hand-built with equivalent rims, hubs, and spokes can be had for only
$275 (provided I dump the discs) with spoke counts up to 36.

3) $275 for a quality ready-built wheelset - $245 for a wheelset built
up on the old hubs = I save only $30 by using the old hubs. (!)
Considering this, you might agree that its a reasonable choice to put
the old hubs in the parts bin and opt for the entirely new wheelset.


For the brake rotors - why are you bending rotors? Unless something
hits them - very, very unlikely on the road - they'll stay true
forever. Even on mountain bikes that are regularly crashed and

abused,
bending a rotor is extremely rare. Other than replacing them when

bent,
there is no "adjustment" required for disk rotors.


I've found the rotors for the Avid mechanical disc brakes are easily
bent or warped: An impact that will damage no other part on the bike
(including electronic components and lighting) may be an impact
powerful enough to bend a rotor. (!!) Thus, when the bike is locked to
a public bike rack (as an example), the rotors are highly vulnerable
to damage ouside my control.

There are other causes of repairable rotor warping that I've heard of.
Sessions of hard braking may exacerbate the warping problem when the
discs get hot. Also, the rotors might have been bent when I purchased
the bike or may be predisposed by unknown defects to warp or bend
easily. I certainly don't know. Whatever the cause, repeated rotor
warp has been an ongoing problem in my experience that strongly
suggests that rims are actually the best brake rotors available for
the riding I do.

Regarding adjustment as required for disc rotors, I'm refering to my
own experience with restoring a rotor to a laterally true state after
it's been repairably bent or warped. I am pleased to report there are
published procedures you can review to see what I'm talking about. At
UtahMoutainBiking.com you can find good information on brake rotor
adjustment.

Straightening a warped rotor:
http://utahmountainbiking.com/fix/diskrotr.htm.

Precision rotor truing:
http://utahmountainbiking.com/fix/diskrotortrue.htm

Special rotor truing tools:
http://www.utahmountainbiking.com/sh...iscbrakes.html

In practice, I've always lacked the special tools that are available
for adjusting the trueness of brake rotors, so I've resorted to less
precise methods that rely upon an adjustable (Cresent-style) wrench,
eyeball measurments, and my bare hands. (Needless to say, I'd love to
have the special tools for rotor adjustment so I could do a precise
job and see how far that would go toward providing a long-lasting
repair.)

To be sure, rotor truing has been one of the mainteance tasks
frequently required for my bike; it's up there with fixing flat tires
and lubricating the chain.


And are you really wearing out disk brake pads? Usually they last

2-3
times what a set of rim brake pads do. On the road I'd expect a set

to
last many years. I find setting up the Avid brakes extremely finicky
and time consuming - just as bad as normal roadie brakes - but at

least
they stay in adjustment for the rest of the year once they're set.


Yes, I really wear out the disc brake pads. (A few days ago I caught
the pads on the remaining disc brake (on the rear) as they were going
metal-to-metal -- the retaining spring had just started to scrape the
rotor -- and then I swapped in the long reach rim caliper.)

After a review of online posts, I think the Avid C4 pads are softer
than most pads, in order to compensate for lower clamping forces
provided by this Avid mechanical (i.e.., not hydraulic) actuation
system that uses conventional road hand levers. These Avid pads have
about the same lifespan as the stock Shimano rim-brake pads I used on
my last road bike. (Surely, I may be using brakes harder than I used
to.)

Yes, the initial setup of the Avid disc-brakes is very finicky, as far
as bicycle maintenance goes, as is the setup of normal road brakes --
I've removed and reinstalled the Avid brakes a few times -- but the
disc caliper positioning has required no further adjustment after
proper setup.

The disc pads do require adjustment to compensate for wear, of course,
and adjustment has been be required on a daily basis when I've done a
lot of hard braking -- a trace of wear on the pads can translate to a
huge increase in travel at the brake lever with the Avid mechanical
disk brakes that were on my bike.

Fortunately, adjusting the disc-brake pads is extremely easy with the
big finger-adjustment knobs on the Avid calipers. Easy, that is,
unless the rotors are warped, in which case the finicky factor
associated with disc-brake adjustment escalates to a level far above
that involved with a complete installation and adjustment of a new rim
brake.

By the way, from more than one retailer one can buy a complete set of
new, long-reach, dual-pivot caliper rim brakes for less than the price
of replacement set of Avid C4 brake pads (!!!)


/* Seattle Mykal */




  #5  
Old July 3rd 05, 12:55 AM
mykal
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Posts: n/a
Default Might Dump Road Disc Brakes for Rim Brakes


Frank wrote:.

It all sounds reasonable to me, except perhaps the last sentence.

I can accept the advantages of disk brakes for muddy conditions that
grind way rims, or for snowy conditions that freeze up the rims and
brakes. But for all the riding I've done in downpours, I can't

recall
enough problems to justify switching to disks.

My only real problem occurred back in the early 1970s, with chrome
steel rims with dimples. On a downhill in a downpour I found I had
_zero_ brakes. But once I could afford a better bike with aluminum
rims, wet weather braking was simply slower, not nonexistent. So I
plan ahead.

Panic stops are extremely rare for me anyway. I'd dump the disks.

- Frank Krygowski


I may have exaggerated the amount of time that rims are really
slippery when I put it at around 10 minutes out of an entire year's
worth of riding.

But if I'm pushing limits in wet conditions I sometimes experience
prolonged instances when rim-brake pads can't seem to get good grip
on the rim. Usually, when things are wet, there's a delay between
brake actuation and braking action; clearly, the pads sometimes need a
little time to squeegee water off the rim before the rubber of the pad
effectively produces friction against the aluminum of the rim. But if
I'm riding through deep puddles or in extremely heavy rain, it seems
to take forever for the pads to starting getting enough friction on
the rim to significantly slow the bike. When the wheels are really
being doused with water (as when coated with mud) the rim brakes
really are practically worthless.

At the same time, I can say I've always found that slowing to a speed
safe for conditions is an inexpensive and effective adaptation to
extremely wet road conditions. Unless, of course, I admit to the
depraved experience of riding a water-pipe "ten speed" that had those
chrome steel rims with dimples that were supposed to provide more
friction for the brake pads but only held more water so the rims would
stay slippery long enough for the rider to exploit the more reliable
friction coefficients associated with cotton denim on asphalt and the
superior stopping power of parked cars.

I can still see the rusty chrome steel rims, the bloody scrapes on my
hands, and the holes in my wet blue jeans.

/* Seattle Mykal */


  #6  
Old July 3rd 05, 08:40 PM
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Default Might Dump Road Disc Brakes for Rim Brakes

I don't work in a bike shop but many of my riding buddys do. They see
this stuff every day. Disk brakes are just a bad idea in almost every
respect except the "bling" factor. It's like a big joke for those who
are inside the loop. It's just something to think about. Don't shoot
the messenger : )

  #7  
Old July 4th 05, 02:13 PM
David Damerell
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Default Might Dump Road Disc Brakes for Rim Brakes

Quoting :
this stuff every day. Disk brakes are just a bad idea in almost every
respect except the "bling" factor. It's like a big joke for those who
are inside the loop. It's just something to think about. Don't shoot
the messenger : )


Wait, I though messengers didn't use brakes at all because they can stop
their fixies in 3 inches at 40mph just with back pressure on the pedals?
--
David Damerell flcl?
Today is Second Monday, Presuary.
  #9  
Old July 5th 05, 12:08 AM
mykal
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Default Might Dump Road Disc Brakes for Rim Brakes

wrote in message
ups.com...
I don't work in a bike shop but many of my riding buddys do. They

see
this stuff every day. Disk brakes are just a bad idea in almost

every
respect except the "bling" factor. It's like a big joke for those

who
are inside the loop. It's just something to think about. Don't shoot
the messenger : )


Message is well taken. Although I don't exactly know what the "bling"
factor is, I've been studying up on the topic and find the term is
commonly used in discussions about new-fangled consumer goods.

While "bling-bling" apparently alludes to a quality of flashiness that
draws consumer appeal of a generally irrational nature, I will confess
that "bling-bling" is also the sound my fingers make as I pry them
away from putting the disc brakes back on my bike.

Sometimes I'm guilty of learning as slow as a Biopace chainring.

/* Seattle Mykal */



  #10  
Old July 5th 05, 03:55 PM
dabac
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Posts: n/a
Default Might Dump Road Disc Brakes for Rim Brakes


mykal Wrote:
....
Anyway, I'm thinking about dumping the disc brakes altogether in favor
of long-reach rim brakes and the simplicity of being able to use
standard wheelsets on the bike. My only reservation is over losing
that quick response time provided by disc brakes when riding through a
downpour: I still think, despite all I've learned, that it might be
good to keep a disc in front for that ten or twenty minutes out of the
year when the rim is soaking wet but I might want to stop in a hurry.


Mavic ceramics does provide decent braking even in the rain,
considerable improvement as compared to rims with aluminum brak
surfaces. But you might have to try a couple of different brake pad
before you find a combo that won't squeak

--
dabac

 




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