K
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
Dawes Sardar. Any other suggestions? Ken
- Status
S
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
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
P
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/
> 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/
T
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
>
> 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
S
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
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
T
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
> 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
S
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
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
W
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 ]
>
> 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 ]
W
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.
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.
T
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
> "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
S
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
[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.
"W K" <[email protected]> wrote in message news
[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.
S
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
>
>
>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
>
>
P
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
> 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
W
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?
> 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?
W
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.
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.
D
David E. Belche
Guest
"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
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
A
Andrew Sweetman
Guest
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
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
D
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...
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...
- Status
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