Disc Brakes for loaded touring

Discussion in 'Cycling Equipment' started by Robert Strickla, Apr 14, 2003.

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  1. Hi everybody,

    I followed a thread about disc brakes a while back in which some folks said that they thought disc
    brakes didn't make sense on a road bike. The arguments made sense to me. It seems likely that you'd
    trade extra hassle, weight and money for no real substantial benefits. What I'm wondering is if you
    all think they make sense for loaded touring. I'm planning to have my steel touring-frame stripped
    and re-painted and I then plan to build up a (mostly Campy) loaded touring bike. I was thinking that
    disc brakes might make sense and since I'm having the frame repainted I might think about adding
    disc brake mounts. Any thoughts on this? I should make clear that I don't have any real knowledge
    about disc brakes. What would be the pro's and con's besides better wet or muddy braking and
    stronger brakes for heavy loads? Thanks in advance.

    Rob Strickland
     
    Tags:


  2. Jobst Brandt

    Jobst Brandt Guest

    Robert Strickland writes:

    > I followed a thread about disc brakes a while back in which some folks said that they thought disc
    > brakes didn't make sense on a road bike. The arguments made sense to me. It seems likely that
    > you'd trade extra hassle, weight and money for no real substantial benefits. What I'm wondering is
    > if you all think they make sense for loaded touring. I'm planning to have my steel touring-frame
    > stripped and re-painted and I then plan to build up a (mostly Campy) loaded touring bike. I was
    > thinking that disc brakes might make sense and since I'm having the frame repainted I might think
    > about adding disc brake mounts. Any thoughts on this? I should make clear that I don't have any
    > real knowledge about disc brakes. What would be the pro's and con's besides better wet or muddy
    > braking and stronger brakes for heavy loads?

    You can't put a disc-brake on a conventional fork safely for two reasons, the fork end cannot
    withstand the bending moment introduced at it's flimsy narrow end, and if you did use one, the front
    wheel would disengage when braking unless you got dropouts with lawyer lips. Hub brakes introduce
    bending moments at the dropout similar to those at the fork crown. That is why fork blades are large
    and oval at the crown.

    You might just go back and read the thread on wheel disengagement of disc-brake bicycles. This stuff
    has not been well thought out. Disk brake bicycles should have conical sunk dropouts so that the up
    and down forces from road and brake do not cause motion.

    Jobst Brandt [email protected] Palo Alto CA
     
  3. Bluto

    Bluto Guest

    "Robert Strickland" <[email protected]> wrote:

    > I followed a thread about disc brakes a while back in which some folks said that they thought disc
    > brakes didn't make sense on a road bike. The arguments made sense to me. It seems likely that
    > you'd trade extra hassle, weight and money for no real substantial benefits. What I'm wondering is
    > if you all think they make sense for loaded touring.
    ...
    > What would be the pro's and con's besides better wet or muddy braking and stronger brakes for
    > heavy loads? Thanks in advance.

    Most disc brakes can't sustain a comparable level of braking power (as continuous watts dissipated)
    to a rim brake with a sturdy touring tire and tube. The way in which they could be called "stronger"
    than a rim brake in a given application is in their ratio of braking torque to lever effort. That
    is, you won't be able to brake any harder or longer with discs before they fail; you just won't have
    to squeeze as hard to get them to that point.

    In addition to the improved wet/muddy braking you mentioned, there are other possible benefits:

    No rim wear from braking Reduced brake smut from wet riding May interfere less with luggage racks
    May allow use of fenders with fatter tires Can allow use of different rim diameters Out-of-true
    wheel less likely to rub

    and possible disadvantages:

    Dished front wheel-- much weaker Rotors seem to warp more easily than rims More vulnerable to damage
    in a tipover Hydraulics fail totally when they fail Dedicated levers for hydraulics Fixed ratio for
    mechanical discs; less tunable than cantis Possibility of QR wheel ejection/lockup (!!)

    For reliability, configurability and proven performance, cantilever brakes still seem like the way
    to go. Unless you crave the ability to swap between 26" and 700c wheels, and have the tire clearance
    to exploit this option, it's hard to make a case for discs on a touring bike.

    If you can't get equal or better braking from cantilever brakes under normal conditions, you're just
    not setting them up to deliver their best.

    That said, disc brakes have improved enough recently that if you want to use them anyway, they
    probably won't disappoint you. Magura and Hayes hydraulics and Avid cable-actuated brakes are all
    pretty safe bets, and bigger rotors appear to be better, all else equal.

    Chalo Colina
     
  4. Robert-<< What I'm wondering is if you all think they make sense for loaded touring.

    I do, loaded touring, tandems, cross bikes, some MTB bikes, hydraulic discs make great sense.

    << I'm planning to have my steel touring-frame stripped and re-painted and I then plan to build up a
    (mostly Campy) loaded touring bike. I was thinking that disc brakes might make sense and since I'm
    having the frame repainted I might think about adding disc brake mounts.

    I think mechanical discs are not much of an improvement over really good cantis tho-all you will be
    able to use with ERGO..

    << What would be the pro's and con's besides better wet or muddy braking and stronger brakes for
    heavy loads?

    May not be number two in the case of mechanicals...

    Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
    (303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"
     
  5. Bluto <[email protected]> wrote:
    >For reliability, configurability and proven performance, cantilever brakes still seem like the
    >way to go.

    There's still a few Suntour self-energising rears out there, too.
    --
    David Damerell <[email protected]> flcl?
     
  6. Matt O'Toole

    Matt O'Toole Guest

    "Bluto" <[email protected]> wrote in message
    news:[email protected]...

    > "Robert Strickland" <[email protected]> wrote:
    >
    > > I followed a thread about disc brakes a while back in
    which some folks said
    > > that they thought disc brakes didn't make sense on a
    road bike. The
    > > arguments made sense to me. It seems likely that you'd
    trade extra hassle,
    > > weight and money for no real substantial benefits. What
    I'm wondering is if
    > > you all think they make sense for loaded touring.
    > ...
    > > What would be the pro's and con's besides better wet or muddy braking and stronger
    brakes for heavy
    > > loads? Thanks in advance.
    >
    > Most disc brakes can't sustain a comparable level of
    braking power (as
    > continuous watts dissipated) to a rim brake with a sturdy
    touring tire
    > and tube. The way in which they could be called
    "stronger" than a rim
    > brake in a given application is in their ratio of braking
    torque to
    > lever effort. That is, you won't be able to brake any
    harder or
    > longer with discs before they fail; you just won't have to
    squeeze as
    > hard to get them to that point.

    This is the heart of the issue. Braking converts kinetic energy to heat, which is dissipated into
    the air. Your wheel rims are larger, and have more mass, than any normal disk brake on the market.
    This means they can dissipate heat better, plus they can absorb more heat without becoming
    incredibly hot.

    In fact most disc brakes sold for MTB use become inadequate on long, high speed descents. And that's
    on trails where really high speeds are hardly reached, and not for long, plus the load is just a
    rider -- no heavy touring bags, etc. A fully loaded touring bike on a long, highway descent would
    overheat these brakes very quickly. Special, larger disc brakes are sold for downhill racing bikes
    and tandems --and they're necessary.

    The advantages of disc brakes are consistency, modulation, and precision, especially where mud
    and dirt can foul the rims. They give more control, and better threshold braking ability.
    However, rim brakes ultimately have more power, that being defined as the ability to dissipate
    heat on a long descent.

    If you really want disc brakes for your touring bike, you'd need larger than normal ones, like
    tandem or downhill racing models. These are specialized equipment and therefore expensive, plus
    they'd probably need specially made forks and frames -- expensive too.

    A drag brake, such as those used by tandem riders, is probably a better solution. However, most
    loaded tourers seem to do without these just fine.

    One thing you might look into are Magura hydraulic rim brakes, which are exremely powerful and
    reliable. If I had a tandem, I'd probably choose these. This would preclude STI/Ergo, though.

    > In addition to the improved wet/muddy braking you
    mentioned, there are
    > other possible benefits:
    >
    > No rim wear from braking Reduced brake smut from wet riding May interfere less with luggage racks
    > May allow use of fenders with fatter tires Can allow use of different rim diameters Out-of-true
    > wheel less likely to rub
    >
    > and possible disadvantages:
    >
    > Dished front wheel-- much weaker Rotors seem to warp more easily than rims More vulnerable to
    > damage in a tipover Hydraulics fail totally when they fail Dedicated levers for hydraulics Fixed
    > ratio for mechanical discs; less tunable than cantis Possibility of QR wheel ejection/lockup (!!)
    >
    > For reliability, configurability and proven performance,
    cantilever
    > brakes still seem like the way to go. Unless you crave
    the ability to
    > swap between 26" and 700c wheels, and have the tire
    clearance to
    > exploit this option, it's hard to make a case for discs on
    a touring
    > bike.
    >
    > If you can't get equal or better braking from cantilever
    brakes under
    > normal conditions, you're just not setting them up to
    deliver their
    > best.
    >
    > That said, disc brakes have improved enough recently that
    if you want
    > to use them anyway, they probably won't disappoint you.
    Magura and
    > Hayes hydraulics and Avid cable-actuated brakes are all
    pretty safe
    > bets,

    All good points.

    > and bigger rotors appear to be better, all else equal.

    The bottom line is that while newer models work very well indeed, there's no getting around the
    smaller size/mass of the rotor, compared to a rim.

    Matt O.
     
  7. Michael

    Michael Guest

    > Disk brake bicycles should have conical sunk dropouts so that the up and down forces from road and
    > brake do not cause motion.

    Can you give more detail? I'm having a custom fork made for a disc-brake road bike, so I'd like to
    build in whatever safety features I can.
     
  8. Doug Huffman

    Doug Huffman Guest

    There is a small but non-negligible force resultant to loading disk brakes oriented to eject the
    wheel from its dropouts. There have also been cases of QRs releasing inadvertently. Lawyer
    lips/conical seating surfaces minimize these possibilities. There has been recent discussion on
    Usenet and a link to a website with detailed descriptions of these possibilities and a free-body
    diagram of the forces involved.

    "Michael" <[email protected]> wrote in message
    news:[email protected]...
    > > Disk brake bicycles should have conical sunk dropouts so that the up and down forces from road
    > > and brake do not cause motion.
    >
    > Can you give more detail? I'm having a custom fork made for a disc-brake road bike, so I'd like to
    > build in whatever safety features I can.
     
  9. Matt O'Toole <[email protected]> wrote:

    : This is the heart of the issue. Braking converts kinetic energy to heat, which is dissipated into
    : the air. Your wheel rims are larger, and have more mass, than any normal disk brake on the market.
    : This means they can dissipate heat better, plus they can absorb more heat without becoming
    : incredibly hot.

    : In fact most disc brakes sold for MTB use become inadequate on long, high speed descents. And
    : that's on trails where really high speeds are hardly reached, and not for long, plus the load is
    : just a rider -- no heavy touring bags, etc. A fully loaded touring bike on a long, highway descent
    : would overheat these brakes very quickly. Special, larger disc brakes are sold for downhill racing
    : bikes and tandems --and they're necessary.

    Disc brakes seem to have become quite popular among recumbents. At least we'll get a fair trial for
    this technology by a reasonable user base in the coming years.

    Interesting points you have. Would cheaper disc brakes like Bitex or Logan be even less reliable and
    effective?

    I've read quite a few comments about how good disc brakes are, like people claiming that theirs
    "never fade on long descents". Does that mean recumbent riders don't view their bikes/trikes
    rationally? (As if anybody did...)

    FWIW, recumbents can be extremely fast on long descents. Also, I consider touring as the
    primary application area for recumbents. (Unless maybe you want to count "day rides" as an
    application area...)

    : The advantages of disc brakes are consistency, modulation, and precision, especially where mud and
    : dirt can foul the rims. They give more control, and better threshold braking ability. However, rim
    : brakes ultimately have more power, that being defined as the ability to dissipate heat on a long
    : descent.

    If your assessment is correct, maybe recumbent communities will eventually migrate back from disc
    brakes, or then conclude that for most applications one doesn't need the braking power, but it's
    nice to have the other benefits instead...

    --
    Risto Varanka | http://www.helsinki.fi/~rvaranka/ varis at no spam please iki fi
     
  10. G.Daniels

    G.Daniels Guest

    1)are shimano's Intel 4 brake units adaptable to a shimano cassette hub.what's 2)inside an intel 4?
    2)is idea one an improvement over a rim setup?
    3)are the brake units seperabl;e from the the hub/trans here?
     
  11. Matt O'Toole

    Matt O'Toole Guest

    <[email protected]> wrote in message
    news:[email protected]...

    > Matt O'Toole <[email protected]> wrote:
    >
    > : This is the heart of the issue. Braking converts
    kinetic
    > : energy to heat, which is dissipated into the air. Your wheel rims are larger, and have more
    > : mass, than any
    normal
    > : disk brake on the market. This means they can dissipate heat better, plus they can absorb more
    > : heat without
    becoming
    > : incredibly hot.
    >
    > : In fact most disc brakes sold for MTB use become
    inadequate
    > : on long, high speed descents. And that's on trails
    where
    > : really high speeds are hardly reached, and not for long, plus the load is just a rider -- no
    > : heavy touring bags,
    etc.
    > : A fully loaded touring bike on a long, highway descent
    would
    > : overheat these brakes very quickly. Special, larger
    disc
    > : brakes are sold for downhill racing bikes and
    tandems --and
    > : they're necessary.
    >
    > Disc brakes seem to have become quite popular among
    recumbents. At
    > least we'll get a fair trial for this technology by a
    reasonable
    > user base in the coming years.
    >
    > Interesting points you have. Would cheaper disc brakes
    like Bitex
    > or Logan be even less reliable and effective?

    I'm not familiar with them, so I have no idea. However, if they're similar to the typical MTB-XC
    type brakes, they're probably undersized to begin with.

    > I've read quite a few comments about how good disc brakes
    are,
    > like people claiming that theirs "never fade on long
    descents".
    > Does that mean recumbent riders don't view their
    bikes/trikes
    > rationally? (As if anybody did...)

    > FWIW, recumbents can be extremely fast on long descents.
    Also, I
    > consider touring as the primary application area for
    recumbents.
    > (Unless maybe you want to count "day rides" as an
    application
    > area...)

    I don't know what disc brakes these recumbent riders are using, or what terrain they're dealing
    with. Are they cruising down 500' hills, or hauling ass down 3000'+ mountains with heavy loads? That
    makes a difference. Are they using typical MTB-XC disc brakes, or oversized ones with rotors
    simlilar in size and mass to a rim (like the ones tandem riders use)?

    > : The advantages of disc brakes are consistency,
    modulation,
    > : and precision, especially where mud and dirt can foul
    the
    > : rims. They give more control, and better threshold
    braking
    > : ability. However, rim brakes ultimately have more
    power,
    > : that being defined as the ability to dissipate heat on a long descent.
    >
    > If your assessment is correct, maybe recumbent communities
    will
    > eventually migrate back from disc brakes, or then conclude
    that for
    > most applications one doesn't need the braking power, but
    it's
    > nice to have the other benefits instead...

    My assessment had nothing to do with what brakes recumbents might be using, but what brakes are
    commonly available for upright bikes -- MTB brakes.

    If recumbent riders are using certain models successfully for high speed descents *with heavy
    loads,* then those models should be adequate for a normal touring bike too, since the loads would be
    similar. However, adapting a touring bike to use them would involve custom work, which is very
    expensive. If you know of a brake that is proven under loads similar to yours, and you don't mind
    paying big bucks to have a bike custom-built to use it, then go ahead.

    Matt O.
     
  12. Matt O'Toole <[email protected]> wrote:
    : I don't know what disc brakes these recumbent riders are using, or what terrain they're dealing
    : with. Are they cruising down 500' hills, or hauling ass down 3000'+ mountains with heavy loads?
    : That makes a difference. Are they using typical MTB-XC disc brakes, or oversized ones with rotors
    : simlilar in size and mass to a rim (like the ones tandem riders use)?

    Basically recumbents use the same parts as upright bikes, the frame is the custom-built (and very
    expensive) part. On mid-range or high-end recumbents, you could see disk brakes like Shimano's M515
    or the models from Magura (hydraulic or mechanical). If you wanted more heavy-duty brakes, many
    manufacturers would probably be happy to install them.

    I'd think most recumbent riders are doing those 500' hills with light load, if even that. (Dutch
    people don't have such hills for example.) I don't know which solutions the heavy touring
    aficionados have found, but at least there are some bikes (or trikes) built specifically for
    heavy touring.

    Would it make sense to for example have disc brakes in front and a rim brake in back? You could use
    the disc brakes for hard braking when you need control, and the rim brake for bleeding off speed
    gradually or for braking when you are going at a slow speed. Also, if you have a trike you could
    have three brakes, which might make the load a bit easier. In practice it might be hairy though,
    since using a rear brake on a (tadpole) trike could cause it to fishtail :-/

    : If recumbent riders are using certain models successfully for high speed descents *with heavy
    : loads,* then those models should be adequate for a normal touring bike too, since the loads would
    : be similar.

    No doubt :)

    : However, adapting a touring bike to use them would involve custom work, which is very expensive.
    : If you know of a brake that is proven under loads similar to yours, and you don't mind paying big
    : bucks to have a bike custom-built to use it, then go ahead.

    Recumbents are very expensive anyway, because production series are very small. Therefore
    customization doesn't hurt that much anymore, but it's more likely that a particular model would be
    designed to use disc brakes, maybe even some particular type of disc brakes, from the start.

    --
    Risto Varanka | http://www.helsinki.fi/~rvaranka/ varis at no spam please iki fi
     
  13. Jobst Brandt

    Jobst Brandt Guest

    Michael Press writes:

    >> Disk brake bicycles should have conical sunk dropouts so that the up and down forces from road
    >> and brake do not cause motion.

    > Can you give more detail? I'm having a custom fork made for a disc-brake road bike, so I'd like to
    > build in whatever safety features I can.

    The outer face of the jam nut, the face that presses against the dropout when the QR is secured,
    should have a conical face, 45 degree included angle would be best. This cone would mate with a
    countersink in a slotted fork dropout. By this means there could be no motion between axle and
    dropout unless the axle or QR skewer broke, something that will not reasonably occur. On the other
    hand, one cannot drop the wheel out merely by opening the QR. The skewer must be unscrewed partly
    after release, the same as with "lawyer lips."

    Jobst Brandt [email protected] Palo Alto CA
     
  14. Dave Lehnen

    Dave Lehnen Guest

    Michael wrote:
    >>Disk brake bicycles should have conical sunk dropouts so that the up and down forces from road and
    >>brake do not cause motion.
    >
    >
    > Can you give more detail? I'm having a custom fork made for a disc-brake road bike, so I'd like to
    > build in whatever safety features I can.

    If you're making a custom fork, have the caliper mount moved from the rear of the left fork leg to
    the front of the right fork leg. You can still use a standard caliper, since the hydraulic line or
    cable will still exit upwards (but the wrong way if you use the front of the left fork leg). What
    was a disengagement force component is now an engagement force component.

    The earliest motorcycles with disc brakes had the calipers in front of the forks. I think they were
    moved behind to keep the caliper mass nearer the steering axis, and nearer the bike's CG. With no
    slotted forks and quick releases, resultant force direction was not an issue.

    Conical surfaces require several non-standard parts, and require either spreading the fork legs
    slightly on installation or having them compressed slightly in the installed state. This would be OK
    for standard forks, but a bad idea for telescopic forks on mountain bikes.

    Dave Lehnen
     
  15. Matt O'Toole

    Matt O'Toole Guest

    "Dave Lehnen" <[email protected]> wrote in message news:[email protected]...

    > Conical surfaces require several non-standard parts, and
    require
    > either spreading the fork legs slightly on installation or
    having
    > them compressed slightly in the installed state. This
    would be OK
    > for standard forks, but a bad idea for telescopic forks on
    mountain
    > bikes.

    There's already an off-the-shelf solution to this problem. Downhill/freeride/whatever MTB forks have
    fully captured axles, along with hubs and QRs to match -- such as the Marzocchi QR20 system.
    Although a conical dropout interface would be easy enough to make, simply copying Marzocchi's fork
    end and using the mating Marzocchi fork parts might be easier and cheaper, depending on the machine
    shop you have access to.

    But again, I wouldn't touch disk brakes for a touring bike unless I knew the ones being considered
    were capable of handling touring loads. I'm not confident that current ones are.

    FWIW, any MTB fork I've played with could easily be spread enough to clear conical axle ends.
    It wouldn't be convenient, but I don't see it as a problem. This includes the new,
    super-stiff Fox Forx.

    Matt O.
     
  16. Grant Sellek

    Grant Sellek Guest

    Disc brakes can outperform rim brakes

    1. on a normal bike. The math shown previously about rims having more metal area so more power
    dissipation is only partly true. It is true if the brake can get equally hot. But a rim cannot be
    allowed to get as hot as a disc rotor. The soft pad of a rim brake (needed for brake
    responsiveness) cannot get as hot. And the tyre bead cannot get as hot. A disc rotor can glow red
    hot and there is no immediate problem. Look at a car.

    2. on a recumbent trike. Disc brakes are the exclusive preferred choice on a tandem recumbent trike.
    Long steep decents on these long fast pigs with rim brakes have overheated and exploded the tyres
    (true experience from a bent trike manufacturer). Not preferred. With 160mm disc brakes there is
    no problem on these big tandem muthas. Other advanteges of disc brakes on the recumbent trike: 1.
    With 2 front wheels more braking force is available. 2. With small front wheels disc brakes
    become effectively much larger. Yum.

    3. someone mentioned drag brakes. Not sure what this means, but if it is the rear drum brakes fitted
    to some tandem bikes, these have very poor performance compared to a disc. Much less power, and
    when they get hot they fade. Disc brakes don't.

    [email protected] wrote ...
    > Matt O'Toole <[email protected]> wrote:
    > : I don't know what disc brakes these recumbent riders are using, or what terrain they're dealing
    > : with. Are they cruising down 500' hills, or hauling ass down 3000'+ mountains with heavy loads?
    > : That makes a difference. Are they using typical MTB-XC disc brakes, or oversized ones with
    > : rotors simlilar in size and mass to a rim (like the ones tandem riders use)?
    >
    > Basically recumbents use the same parts as upright bikes, the frame is the custom-built (and very
    > expensive) part. On mid-range or high-end recumbents, you could see disk brakes like Shimano's
    > M515 or the models from Magura (hydraulic or mechanical). If you wanted more heavy-duty brakes,
    > many manufacturers would probably be happy to install them.
    >
    > I'd think most recumbent riders are doing those 500' hills with light load, if even that. (Dutch
    > people don't have such hills for example.) I don't know which solutions the heavy touring
    > aficionados have found, but at least there are some bikes (or trikes) built specifically for heavy
    > touring.
    >
    > Would it make sense to for example have disc brakes in front and a rim brake in back? You could
    > use the disc brakes for hard braking when you need control, and the rim brake for bleeding off
    > speed gradually or for braking when you are going at a slow speed. Also, if you have a trike you
    > could have three brakes, which might make the load a bit easier. In practice it might be hairy
    > though, since using a rear brake on a (tadpole) trike could cause it to fishtail :-/
    >
    > : If recumbent riders are using certain models successfully for high speed descents *with heavy
    > : loads,* then those models should be adequate for a normal touring bike too, since the loads
    > : would be similar.
    >
    > No doubt :)
     
  17. [email protected] wrote in message news:<[email protected]>...
    > Robert Strickland writes:
    >
    > > I followed a thread about disc brakes a while back in which some folks said that they thought
    > > disc brakes didn't make sense on a road bike. The arguments made sense to me. It seems likely
    > > that you'd trade extra hassle, weight and money for no real substantial benefits. What I'm
    > > wondering is if you all think they make sense for loaded touring. I'm planning to have my steel
    > > touring-frame stripped and re-painted and I then plan to build up a (mostly Campy) loaded
    > > touring bike. I was thinking that disc brakes might make sense and since I'm having the frame
    > > repainted I might think about adding disc brake mounts. Any thoughts on this? I should make
    > > clear that I don't have any real knowledge about disc brakes. What would be the pro's and con's
    > > besides better wet or muddy braking and stronger brakes for heavy loads?
    >
    > You can't put a disc-brake on a conventional fork safely for two reasons, the fork end cannot
    > withstand the bending moment introduced at it's flimsy narrow end, and if you did use one, the
    > front wheel would disengage when braking unless you got dropouts with lawyer lips. Hub brakes
    > introduce bending moments at the dropout similar to those at the fork crown. That is why fork
    > blades are large and oval at the crown.
    >
    > You might just go back and read the thread on wheel disengagement of disc-brake bicycles. This
    > stuff has not been well thought out. Disk brake bicycles should have conical sunk dropouts so that
    > the up and down forces from road and brake do not cause motion.
    >
    > Jobst Brandt [email protected] Palo Alto CA

    This time Jobst is right. If you keep trying long enough you'll get it.
     
  18. Grant Sellek <[email protected]> wrote:
    : Disc brakes can outperform rim brakes

    Thanks for the points... something to consider! :)

    : 3. someone mentioned drag brakes. Not sure what this means, but if it is the rear drum brakes
    : fitted to some tandem bikes, these have very poor performance compared to a disc. Much less
    : power, and when they get hot they fade. Disc brakes don't.

    Hmm wasn't it a rear rim brake operated by a friction gear lever? So you can crank the lever to a
    fixed position and have about constant braking force on the rear rim for the whole descent... just
    something to take a bit of load from the front brakes.

    --
    Risto Varanka | http://www.helsinki.fi/~rvaranka/ varis at no spam please iki fi
     
  19. Grant Sellek wrote:
    > Disc brakes can outperform rim brakes

    It depends on the criteria by which you judge perform.

    Braking force? Nope. On single bikes, for example, brake force is limited by the pitchover point.
    Even the lowly single pivot rim brake can produce this much force. On soft surfaces (off-road) the
    limit of braking may be even less, limited by tire traction.

    Elimination of brake fade? Nope. See below.

    Lower weight and cost? Nope.

    > 1. on a normal bike. The math shown previously about rims having more metal area so more power
    > dissipation is only partly true. It is true if the brake can get equally hot. But a rim cannot
    > be allowed to get as hot as a disc rotor. The soft pad of a rim brake (needed for brake
    > responsiveness) cannot get as hot. And the tyre bead cannot get as hot. A disc rotor can glow
    > red hot and there is no immediate problem. Look at a car.

    Bicycle disk brakes also can not be allowed to get too hot. They can and do fail due to overheating.
    According to some published tests, many models of disk brakes fail at lower power dissipation levels
    than tires fail with rim brakes. See the link below for some test results:

    http://www.ihpva.org/pipermail/hpv/Week-of-Mon-20020304/023003.html

    >
    > 2. on a recumbent trike. Disc brakes are the exclusive preferred choice on a tandem recumbent
    > trike.

    The most likely reason that disk brakes are popular for trikes is simply because they are
    easier to mount.

    > 3. someone mentioned drag brakes. Not sure what this means,

    Since you are such an expert on bicycle brakes, it is hard to believe you never heard of a
    drag brake.

    > but if it is the rear drum brakes fitted to some tandem bikes, these have very poor performance
    > compared to a disc. Much less power, and when they get hot they fade. Disc brakes don't.

    Drag brakes are not intended as the primary braking device. A drum drag brake is used in
    conjunction with rim brakes typically gives better performance than disk brakes. More information
    on this can be found at:

    http://tandem-fahren.de/Mitglieder/Christoph_Timm/DiskFAQ.html

    Mark McMaster [email protected]
     
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