Road bike with disk mounts

Discussion in 'UK and Europe' started by Ken, Apr 14, 2003.

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  1. Ken

    Ken Guest

    Looking for a road bike or frameset with fittings for disk brakes. I'm aware of the Kona Dr Dew and
    Dawes Sardar. Any other suggestions? Ken
     
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  2. Si Davies

    Si Davies Guest

    canondale used to do a tourer with discs - may have discontinued it now.

    you can get bolt on rear mounts that may fit some frames, eg the forge one. and if you get a steel
    touring fork for the front end of your bike then a frame builder wil be able to weld a mount on.

    "Ken" <[email protected]> wrote in message news:[email protected]...
    > Looking for a road bike or frameset with fittings for disk brakes. I'm
    aware
    > of the Kona Dr Dew and Dawes Sardar. Any other suggestions? Ken
     
  3. Peter Clinch

    Peter Clinch Guest

    Ken wrote:
    > Looking for a road bike or frameset with fittings for disk brakes. I'm aware of the Kona Dr Dew
    > and Dawes Sardar. Any other suggestions?

    The Sardar suggests you're meaning road bike as in "bike for the road" rather than minimalist
    sporting machinery, in which case I'll suggest The Dark Side. Plenty of 'bents come with discs as
    standard, or at least a standard option fitted on order.

    Pete.
    --
    Peter Clinch University of Dundee Tel 44 1382 660111 ext. 33637 Medical Physics, Ninewells Hospital
    Fax 44 1382 640177 Dundee DD1 9SY Scotland UK net [email protected]
    http://www.dundee.ac.uk/~pjclinch/
     
  4. Tony Raven

    Tony Raven Guest

    Si Davies <[email protected]> wrote:
    >
    > if you get a steel touring fork for the front end of your bike then a frame builder wil be able to
    > weld a mount on.
    >

    Bad advice. Most rigid forks are totally unsuitable to handle the torque and one sided loading of
    disk brakes. If it doesn't have tabs on from new or hasn't been custom built by someone that really
    knows what they are doing don't do it.

    Try having a look at some cross bike which are increasingly designed for and fitted with disks.

    Tony

    -- http://www.raven-family.com

    "The reasonable man adapts himself to the world; the unreasonable man persists in trying to
    adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
    Bernard Shaw
     
  5. Si Davies

    Si Davies Guest

    There were similar arguments to this when V brakes first emerged and people wanted to put them on
    road bikes. The torque will be little different to a really good none disk brake - either one will
    stop the wheel and chuck you over the bars if you hit it hard enough - the advantage a disc gives is
    that it has very good modulation and works in all weathers and conditions. Remember the weakest part
    of a fork is at the crown - therefore it makes little difference if the brake is at the rim or the
    hub - the pivot point is where the tyre touches the road. And I didn't say 'most rigid forks' i said
    a steel touring fork - i.e. a strong fork that can take the weight of luggage on a loaded bike and
    thus should give no problems with a disc. As for having the disc on one side, again i don't see the
    problem - causes no problems on telescopic forks which you would think should twist a lot more than
    rigid ones. By all means have a fork specially built but you will just end up with a strong, over
    built fork (funnily enough, like what you find on tourers) with a disc mount welded on it!

    "Tony Raven" <[email protected]> wrote in message news:[email protected]...
    > Si Davies <[email protected]> wrote:
    > >
    > > if you get a steel touring fork for the front end of your bike then a frame builder wil be able
    > > to weld a mount on.
    > >
    >
    > Bad advice. Most rigid forks are totally unsuitable to handle the torque and one sided loading of
    > disk brakes. If it doesn't have tabs on from new or hasn't been custom built by someone that
    > really knows what they are
    doing
    > don't do it.
    >
    > Try having a look at some cross bike which are increasingly designed for and fitted with disks.
    >
    > Tony
    >
    > -- http://www.raven-family.com
    >
    > "The reasonable man adapts himself to the world; the unreasonable man persists in trying to
    > adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
    > Bernard Shaw
     
  6. Tony Raven

    Tony Raven Guest

    Si Davies <[email protected]> wrote:
    > There were similar arguments to this when V brakes first emerged and people wanted to put them on
    > road bikes. The torque will be little different to a really good none disk brake - either one will
    > stop the wheel and chuck you over the bars if you hit it hard enough - the advantage a disc gives
    > is that it has very good modulation and works in all weathers and conditions. Remember the weakest
    > part of a fork is at the crown - therefore it makes little difference if the brake is at the rim
    > or the hub - the pivot point is where the tyre touches the road. And I didn't say 'most rigid
    > forks' i said a steel touring fork - i.e. a strong fork that can take the weight of luggage on a
    > loaded bike and thus should give no problems with a disc. As for having the disc on one side,
    > again i don't see the problem - causes no problems on telescopic forks which you would think
    > should twist a lot more than rigid ones. By all means have a fork specially built but you will
    > just end up with a strong, over built fork (funnily enough, like what you find on tourers) with a
    > disc mount welded on it!
    >

    Is the wrong answer. Torque is not stopping power, it is the twisting force created by the brakes
    and is very different between rim and disk brakes. Rim brakes produce symmetrical torque loading on
    the fork. Disk brakes provide loading on the one leg holding the calipers. Suspension forks are very
    rigid between the mounting point of the disk brake caliper and the axle. Rigid forks, especially
    touring forks, are designed to have flex in the fork legs to provide some suspension. With
    assymetric loading and the different mounting position of the caliper from rim brakes that puts an
    assymetric bending load on the fork legs they were not designed for. The left fork leg is pushed
    back while the right leg is unaffected.

    Tony

    --
    http://www.raven-family.com

    "The reasonable man adapts himself to the world; the unreasonable man persists in trying to
    adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
    Bernard Shaw
     
  7. Si Davies

    Si Davies Guest

    >Torque is not stopping power
    don't believe i said it was.. If there was so much extra force going through one fork leg during
    stopping then the handle bars would twist as you applied the brakes :-
    >"The left fork leg is pushed back while the right leg is unaffected."
    I'm not denying that this happens but but the force is not suficient to feel in the bars, thus
    cannot be sufficient to bend the fork. Pretty simple really. On a thin race fork it may bend - i can
    bend one with my arms, but on a heavy duty touring fork it won't.

    >>. Suspension forks are very rigid between the mounting point of the disk
    brake caliper and the
    > axle.
    Not always the case, mine's been clamped onto a carbon leg for three years with no trouble at all.
    But that's by the by, the pint is that even when not braking a telescopic fork will not track as
    well as a rigid one. Thus there must be more 'flex' between the two halfs of each leg than in a
    rigid leg. This should then be amplified during braking wioth a disc and cause problems, but it
    doesn't because despite there being a force there, it's not big enough to cause problems.

    Just out of interest, if I was about to go off and weld up a disc specific fork (from scratch), how
    would you instruct me to make it different to a standard touring fork? This was a question i asked a
    frame builder who said the same about discs as you - his reason for not fitting discs on a tourer
    was "because you can't" and he couldn't answer this question, so I'm interested to know what they do
    on these cx disc forks that make them different?

    "Tony Raven" <[email protected]> wrote in message news:[email protected]...
    > Si Davies <[email protected]> wrote:
    > > There were similar arguments to this when V brakes first emerged and people wanted to put them
    > > on road bikes. The torque will be little different to a really good none disk brake - either one
    > > will stop the wheel and chuck you over the bars if you hit it hard enough - the advantage a disc
    > > gives is that it has very good modulation and works in all weathers and conditions. Remember the
    weakest
    > > part of a fork is at the crown - therefore it makes little difference if the brake is at the rim
    > > or the hub - the pivot point is where the tyre touches the road. And I didn't say 'most rigid
    > > forks' i said a steel touring fork - i.e. a strong fork that can take the weight of luggage on a
    > > loaded bike and thus should give no problems with a disc. As for having the disc on one side,
    > > again i don't see the problem -
    causes
    > > no problems on telescopic forks which you would think should twist a lot more than rigid ones.
    > > By all means have a fork specially built but you will just end up with a strong, over built fork
    > > (funnily enough, like what you find on tourers) with a disc mount welded on it!
    > >
    >
    > Is the wrong answer. Torque is not stopping power, it is the twisting
    force
    > created by the brakes and is very different between rim and disk brakes. Rim brakes produce
    > symmetrical torque loading on the fork. Disk brakes provide loading on the one leg holding the
    > calipers. Suspension forks are very rigid between the mounting point of the disk brake caliper and
    > the axle. Rigid forks, especially touring forks, are designed to have flex in the fork legs to
    > provide some suspension. With assymetric loading and the different mounting position of the
    > caliper from rim brakes that puts an assymetric bending load on the fork legs they were not
    > designed for. The left fork leg is pushed back while the right leg is unaffected.
    >
    > Tony
    >
    > --
    > http://www.raven-family.com
    >
    > "The reasonable man adapts himself to the world; the unreasonable man persists in trying to
    > adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
    > Bernard Shaw
     
  8. W K

    W K Guest

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

    >
    > Is the wrong answer. Torque is not stopping power, it is the twisting
    force
    > created by the brakes and is very different between rim and disk brakes.

    Is incorrect (unless you are thinking of a torque around somewhere other than the hub). The torque
    is the same for the same decelleration (or perhaps easier to imagine is the same whilst holding
    yourself stationary on a 15% slope). What is important is how that equal torque translates into
    force on the fork. As torque is force x distance , if a rim brake is held on the fork 30cm from the
    hub and a disk brake mount is 6 cm from the hub then there will be 5x more force on the brake mount
    for the disk version.

    Well designed and sturdy touring/cross equipment would cope.

    [ snip stuff about symetry - I'd have thought the asymetry was more about doubling the force by only
    having it one side ]
     
  9. W K

    W K Guest

    "Si Davies" <[email protected]> wrote in message
    news:W_Rma.7351$8%[email protected]...
    > >Torque is not stopping power
    > don't believe i said it was.. If there was so much extra force going through one fork leg during
    stopping
    > then the handle bars would twist as you applied the brakes :-

    Wrong. Hard to see immediately why, but the mounts of the disc brake is on one side of the fork and
    IS exerting a force on that specific area of one fork - and is the only force slowing you down.
     
  10. Tony Raven

    Tony Raven Guest

    W K <[email protected]> wrote:
    > "Tony Raven" <[email protected]> wrote in message
    > news:[email protected]...
    >
    >>
    >> Is the wrong answer. Torque is not stopping power, it is the twisting force created by the brakes
    >> and is very different between rim and disk brakes.
    >
    > Is incorrect (unless you are thinking of a torque around somewhere other than the hub).

    One more time.

    On rim brakes the brake pads are attempting to stop the wheel turning. This provides a reaction
    force at the dropouts which is attempting to force the dropouts on *both* sides backwards. The lever
    arm is the entire length of the fork blade and results mainly in the thick end of the fork blade
    attempting to twist backwards in the crown.

    On a disk brake the caliper pads are attempting to stop the disk rotating. This provides a reaction
    force on the dropout on the side the caliper is mounted. This is attempting to twist the fork blade
    back on that side pivoting about the caliper mount. The other dropout sees the hub twisting and is
    forced forward by that twisting force (exactly the opposite to the rim brake case).

    The end of rigid forks for road bikes are usually thin and curved to provide some flex. The fork
    blade is not designed in general to take those sorts of forces in those places, especially a bending
    force about a fulcrum near the bottom (thin) end of the blade.

    The torque at the left dropout is double with a disk brake for the same deceleration as with a rim
    brake (which spreads it over two dropouts) and the point at which the forces are applied to create
    that torque are different (hub plus near the crown and near the tip respectively). As you point out
    the forces on the drop out are much higher.

    > The torque is the same for the same decelleration (or perhaps easier to imagine is the same whilst
    > holding yourself stationary on a 15% slope). What is important is how that equal torque translates
    > into force on the fork.

    No it doesn't. The forces are applied to one side only and in a very different place on the
    fork blade

    > Well designed and sturdy touring/cross equipment would cope.

    It may or may not. Some forks will be able to handle it and some won't. There is no way to easily
    tell which is which if it was not an intention of their design.

    If you don't believe me the following is a quote from Jobst Brandt on rbt:

    "What is less apparent, is that a disk brake puts the same bending force that appears at the fork
    crown on the end of the single fork blade at the caliper.

    This severe bending moment is the reason not to put a disk brake on a conventional bicycle (road)
    fork with a slender blade end, an end that is not intended to carry bending loads like those at the
    large diameter end at the fork crown."

    Tony

    --
    http://www.raven-family.com

    "The reasonable man adapts himself to the world; the unreasonable man persists in trying to
    adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
    Bernard Shaw
     
  11. Si Davies

    Si Davies Guest

    aha, my point exactly! it doesn't twist the fork around when you hit the brake.

    "W K" <[email protected]> wrote in message news:eek:[email protected]...
    >
    > "Si Davies" <[email protected]> wrote in message
    > news:W_Rma.7351$8%[email protected]...
    > > >Torque is not stopping power
    > > don't believe i said it was.. If there was so much extra force going through one fork leg during
    > stopping
    > > then the handle bars would twist as you applied the brakes :-
    >
    > Wrong. Hard to see immediately why, but the mounts of the disc brake is on one side of the
    > fork and IS exerting a force on that specific area of one fork - and is the only force slowing
    > you down.
     
  12. Si Davies

    Si Davies Guest

    >> Well designed and sturdy touring/cross equipment would cope.

    >It may or may not.

    exactly my point - if you have a fork that you know is strong enough to take the force then you are
    OK. Same thing applies to luggage - in general you wouldn't want to be kitchen sink touring on a
    light weight road bike (even if it had all the braze ons). However, that doesn't mean that all light
    road bikes will fall apart on a overloaded tour.

    So what we are all saying is that some forks ARE strong enough (even if not specifically designed
    for the task) and some AREN'T. I think I shall exit stage left and go for a ride now before any more
    confusion ensues.... :)

    "Tony Raven" <[email protected]> wrote in message news:[email protected]...
    > W K <[email protected]> wrote:
    > > "Tony Raven" <[email protected]> wrote in message
    > > news:[email protected]...
    > >
    > >>
    > >> Is the wrong answer. Torque is not stopping power, it is the twisting force created by the
    > >> brakes and is very different between rim and disk brakes.
    > >
    > > Is incorrect (unless you are thinking of a torque around somewhere other than the hub).
    >
    > One more time.
    >
    > On rim brakes the brake pads are attempting to stop the wheel turning.
    This
    > provides a reaction force at the dropouts which is attempting to force the dropouts on *both*
    > sides backwards. The lever arm is the entire length of the fork blade and results mainly in the
    > thick end of the fork blade attempting to twist backwards in the crown.
    >
    > On a disk brake the caliper pads are attempting to stop the disk rotating. This provides a
    > reaction force on the dropout on the side the caliper is mounted. This is attempting to twist
    > the fork blade back on that side pivoting about the caliper mount. The other dropout sees the
    > hub twisting and is forced forward by that twisting force (exactly the opposite to the rim
    > brake case).
    >
    > The end of rigid forks for road bikes are usually thin and curved to
    provide
    > some flex. The fork blade is not designed in general to take those sorts
    of
    > forces in those places, especially a bending force about a fulcrum near
    the
    > bottom (thin) end of the blade.
    >
    > The torque at the left dropout is double with a disk brake for the same deceleration as with a rim
    > brake (which spreads it over two dropouts) and the point at which the forces are applied to create
    > that torque are different (hub plus near the crown and near the tip respectively). As you point
    > out the forces on the drop out are much higher.
    >
    > > The torque is the same for the same decelleration (or perhaps easier to imagine is the same
    > > whilst holding yourself stationary on a 15% slope). What is important is how that equal torque
    > > translates into force on the fork.
    >
    > No it doesn't. The forces are applied to one side only and in a very different place on the
    > fork blade
    >
    > > Well designed and sturdy touring/cross equipment would cope.
    >
    > It may or may not. Some forks will be able to handle it and some won't. There is no way to easily
    > tell which is which if it was not an intention
    of
    > their design.
    >
    > If you don't believe me the following is a quote from Jobst Brandt on rbt:
    >
    > "What is less apparent, is that a disk brake puts the same bending force that appears at the fork
    > crown on the end of the single fork blade at the caliper.
    >
    > This severe bending moment is the reason not to put a disk brake on a conventional bicycle (road)
    > fork with a slender blade end, an end that is not intended to carry bending loads like those at
    > the large diameter end at the fork crown."
    >
    > Tony
    >
    > --
    > http://www.raven-family.com
    >
    > "The reasonable man adapts himself to the world; the unreasonable man persists in trying to
    > adapt the world to himself. Therefore, all progress depends on the unreasonable man." -- George
    > Bernard Shaw
    >
    >
     
  13. Pete Biggs

    Pete Biggs Guest

    Si Davies wrote:

    > So what we are all saying is that some forks ARE strong enough (even if not specifically designed
    > for the task) and some AREN'T.

    That may well be true, but how can you know which ones will be strong enough? From what I've read so
    far, I wouldn't risk a disc brake on anything other than a fork designed specifically for the job.

    ~PB
     
  14. W K

    W K Guest

    "Tony Raven" <[email protected]> wrote in message news:[email protected]...
    > W K <[email protected]> wrote:
    > > "Tony Raven" <[email protected]> wrote in message
    > > news:[email protected]...
    > >
    > >>
    > >> Is the wrong answer. Torque is not stopping power, it is the twisting force created by the
    > >> brakes and is very different between rim and disk brakes.
    > >
    > > Is incorrect (unless you are thinking of a torque around somewhere other than the hub).
    >
    > One more time.

    [ why I got what you said ?]

    > > The torque is the same for the same decelleration (or perhaps easier to imagine is the same
    > > whilst holding yourself stationary on a 15% slope). What is important is how that equal torque
    > > translates into force on the fork.
    >
    > No it doesn't. The forces are applied to one side only

    OK, but its still the same torque, one place rather than two.

    > and in a very different place on the fork blade

    OK, but its still the same braking torque.

    > If you don't believe me the following is a quote from Jobst Brandt on rbt:
    ha!

    > "What is less apparent, is that a disk brake puts the same bending force that appears at the fork
    > crown on the end of the single fork blade at the caliper.

    I don't know quite what he means bu "the end" there.

    > This severe bending moment is the reason not to put a disk brake on a conventional bicycle (road)
    > fork with a slender blade end, an end that is not intended to carry bending loads like those at
    > the large diameter end at the fork crown."

    Thats perhaps what could be described as "breaking" rather than "breaking" torque. Where would you
    say the pivot on the force he mentions there is? Perhaps at the caliper mounts?
     
  15. W K

    W K Guest

    "Si Davies" <[email protected]> wrote in message
    news:iMTma.9449$8%[email protected]...
    > aha, my point exactly! it doesn't twist the fork around when you hit the brake.

    That shows a poor understanding of the physics though.

    Unless you actually had each fork arm attatched to independend handlebars with separate pivots you
    wouldn't feel the difference.

    The different forces on the two sides might attempt to break the forks, but do not put any turning
    force on the handlebars.
     
  16. "Tony Raven" <[email protected]> wrote in message
    news:<[email protected]>...
    >
    > Try having a look at some cross bike which are increasingly designed for and fitted with disks.
    >

    For starters; Cannondale's disc-braked 'cross bike, which might also be available as a frameset, and
    the Kinesis Crosslight 2 (frame + fork only). Mavic have also introduced a disc-compatible
    ready-built 700c wheelset for 2003 called the SpeedCity, which might be worth checking out if
    building a machine from one of the aforementioned framesets. To be honest, based on my own
    experiences, I've yet to see a disc-braked 'cross bike used in anger in a UK race; even top-level
    riders like Keith Murray and Steve Knight seem to opt for cantis on their Kinesis Crosslight 2s.

    David E. Belcher

    Dept. of Chemistry, University of York
     
  17. Pete Biggs <pLime{remove_fruit}@biggs.tc> wrote in message
    news:[email protected]...
    > Si Davies wrote:
    >
    > > So what we are all saying is that some forks ARE strong enough (even if not specifically
    > > designed for the task) and some AREN'T.
    >
    > That may well be true, but how can you know which ones will be strong enough? From what I've
    > read so far, I wouldn't risk a disc brake on anything other than a fork designed specifically
    > for the job.
    >

    I have seen photos of a fork bent backwards at mid-height, and that was from the torque arm of a
    drum brake.

    You may also like to consider the problem of a disk brake twisting the QR out of the dropouts - see
    the thread "updated web page on disk brakes and quick releases" OP James Annan, and google for
    "Russell Pinder" to see the possible consequences of a front wheel coming off at speed on a descent.

    Andrew
     
  18. Dave Kahn

    Dave Kahn Guest

    "Si Davies" <[email protected]> wrote in message
    news:<W_Rma.7351$8%[email protected]>...
    >
    > Just out of interest, if I was about to go off and weld up a disc specific fork (from scratch),
    > how would you instruct me to make it different to a standard touring fork? This was a question i
    > asked a frame builder who said the same about discs as you - his reason for not fitting discs on a
    > tourer was "because you can't" and he couldn't answer this question...

    Sounds like a frame builder to trust. While "because you can't" may not be strictly true, he was
    wise enough to realise that he did not understand enough about the problem to do a safe and
    reliable job.

    --
    Dave...
     
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