J
James Annan
Guest
Some of you may have seen this on singletrackworld.com. I'll post my reply shortly. (For those who
don't know, Pace are a UK MTB fork manufacturer.)
James
---------------
Disc-brakes and QR's An Open Letter from Pace Cycles
The possibility of a quick release wheel disengaging from a dropout is an important issue and
certainly requires careful scrutiny. This seems and obvious thing to say (and we say this as a fork
manufacturer, not as a representative of other manufacturers). In this respect Pace feels that the
responsibility rests equally between the parts manufacturers and the user. Manufacturers have to
make sure that the design has integrity, fitness for purpose, and meets all acceptable standards,
whilst the user must fit and use the product correctly, checking the product before each ride.
I guess Mr Campagnolo laboured over these issues long and hard when he designed the QR, after all we
all want a quick release and the convenience it offers, but without compromising safety. No
cross-country rider that I'm aware of has come to Pace asking for a Slow Release. And when a new
product is introduced into a proven assembly (disc-brakes) then manufacturers must re-examine the
overall assembly. I guess in this respect the onus here lies with the disc brake manufacturer as any
manufacturer designing a new product must make sure it is compatible (in every respect) with
interfacing parts before confidently releasing onto the open market (the wide usage of dropouts
coming before the wide acceptance of disc-brakes that is).
Only a cynic would say that manufacturers would prefer to ignore issues such as these and not offer
an opinion. The truth is I suspect that we would all prefer to stay low profile, as in these
litigious days offering a view might make them liable ( and I would have to say this statement is
made without prejudice) however Pace does not base its designs on unproven principles. I think that
much of the debate and investigative work which has been done and referred to so far ( Bike Magic
and other sites) has approached the matter correctly i.e. let mathematics and the laws of physics
support design and application hypothesis. Subjective views can be dangerous.
>From our past R&D one important influencing factor is brake calliper
position and this should not be confused with ISO disc-brake mounting standards. Pace forks are
designed to meet ISO standard but this does not prevent a brake manufacturer from designing a
calliper so as to pick up on the ISO mounts but actually position the pads anywhere on the disc.
Most certainly it is the case that the closer the pad is aligned to the dropout angle the lower the
disengaging force whilst the more the pad is located perpendicular to the dropout angle the higher
the disengaging force. Generally this means callipers tucked up against the slider leg are a
positive in this respect, those hung out in the wind are not.
Specifically then, from our analysis there is a reaction at the wheel spindle which has a
disengaging force. If we take it that the dropout slot itself is conventional we can expect it to be
approximately parallel to the
c/l of the slider with varying degrees of offset designed into the fork crown. This accepted, unless
the dropout has an unorthodox design where it is angled rearwards following a radius springing
from the centre of the brake pad, this disengaging factor must be less than unity.
I think it can be accepted that there is no forward moving reaction.
To disengage the wheel spindle from the dropout the distance from wheel spindle c/l and brake-pad
reaction c/l must increase whilst the force resisting this movement across the disc is the brake
pad reaction.
Since the disengaging component of this force is less than unity then in our view the spindle
will not disengage through brake action alone. It follows then that although pad position
relative to fork c/l does effect the disengaging force the force can never be greater than that
exerted by the pad.
This tells us that in itself a disc brake will not disengage a wheel OR which is correctly fitted
and tightened (not withstanding points above).
One very important addendum on the last point. Pace have found a few brands of OR that actually
loosen slightly as lever finally closes. Make sure the OR used works correctly and can be tightened
to the manufacturers spec' and this meets ISO standards.
Another important footnote is that because of the dynamics created through 'fluttering' brakes
strange effects can be created (as can poorly adjusted fork damper settings) such as a form of
harmonic. Pace has not undertaken any analysis of this phenomenon.
Personally speaking I have had the experience of a front wheel disengaging and luckily I came away
with dented pride rather than a dented face. However over many years of mountain biking I have also
experienced a disengaged rear wheel (OK laughs all round), however the calliper was positioned such
that there would have been a positive force pushing the spindle back into the dropout. A positive
engaging force so to speak. Obviously my fault not tightening the QR correctly- not weird science.
If we as riders make mistakes such as this, with respect, we should hold our hand up- not try and
place the blame elsewhere.
In summary I guess Pace are saying there can be a variable depending upon dropout design, calliper
design, OR design and correct fitting by the rider. But our view is that as long as all products are
designed correctly and the rider fits the OR and torques it up correctly the wheel will not
disengage.
Adrian Carter Pace Cycles Limited
don't know, Pace are a UK MTB fork manufacturer.)
James
---------------
Disc-brakes and QR's An Open Letter from Pace Cycles
The possibility of a quick release wheel disengaging from a dropout is an important issue and
certainly requires careful scrutiny. This seems and obvious thing to say (and we say this as a fork
manufacturer, not as a representative of other manufacturers). In this respect Pace feels that the
responsibility rests equally between the parts manufacturers and the user. Manufacturers have to
make sure that the design has integrity, fitness for purpose, and meets all acceptable standards,
whilst the user must fit and use the product correctly, checking the product before each ride.
I guess Mr Campagnolo laboured over these issues long and hard when he designed the QR, after all we
all want a quick release and the convenience it offers, but without compromising safety. No
cross-country rider that I'm aware of has come to Pace asking for a Slow Release. And when a new
product is introduced into a proven assembly (disc-brakes) then manufacturers must re-examine the
overall assembly. I guess in this respect the onus here lies with the disc brake manufacturer as any
manufacturer designing a new product must make sure it is compatible (in every respect) with
interfacing parts before confidently releasing onto the open market (the wide usage of dropouts
coming before the wide acceptance of disc-brakes that is).
Only a cynic would say that manufacturers would prefer to ignore issues such as these and not offer
an opinion. The truth is I suspect that we would all prefer to stay low profile, as in these
litigious days offering a view might make them liable ( and I would have to say this statement is
made without prejudice) however Pace does not base its designs on unproven principles. I think that
much of the debate and investigative work which has been done and referred to so far ( Bike Magic
and other sites) has approached the matter correctly i.e. let mathematics and the laws of physics
support design and application hypothesis. Subjective views can be dangerous.
>From our past R&D one important influencing factor is brake calliper
position and this should not be confused with ISO disc-brake mounting standards. Pace forks are
designed to meet ISO standard but this does not prevent a brake manufacturer from designing a
calliper so as to pick up on the ISO mounts but actually position the pads anywhere on the disc.
Most certainly it is the case that the closer the pad is aligned to the dropout angle the lower the
disengaging force whilst the more the pad is located perpendicular to the dropout angle the higher
the disengaging force. Generally this means callipers tucked up against the slider leg are a
positive in this respect, those hung out in the wind are not.
Specifically then, from our analysis there is a reaction at the wheel spindle which has a
disengaging force. If we take it that the dropout slot itself is conventional we can expect it to be
approximately parallel to the
c/l of the slider with varying degrees of offset designed into the fork crown. This accepted, unless
the dropout has an unorthodox design where it is angled rearwards following a radius springing
from the centre of the brake pad, this disengaging factor must be less than unity.
I think it can be accepted that there is no forward moving reaction.
To disengage the wheel spindle from the dropout the distance from wheel spindle c/l and brake-pad
reaction c/l must increase whilst the force resisting this movement across the disc is the brake
pad reaction.
Since the disengaging component of this force is less than unity then in our view the spindle
will not disengage through brake action alone. It follows then that although pad position
relative to fork c/l does effect the disengaging force the force can never be greater than that
exerted by the pad.
This tells us that in itself a disc brake will not disengage a wheel OR which is correctly fitted
and tightened (not withstanding points above).
One very important addendum on the last point. Pace have found a few brands of OR that actually
loosen slightly as lever finally closes. Make sure the OR used works correctly and can be tightened
to the manufacturers spec' and this meets ISO standards.
Another important footnote is that because of the dynamics created through 'fluttering' brakes
strange effects can be created (as can poorly adjusted fork damper settings) such as a form of
harmonic. Pace has not undertaken any analysis of this phenomenon.
Personally speaking I have had the experience of a front wheel disengaging and luckily I came away
with dented pride rather than a dented face. However over many years of mountain biking I have also
experienced a disengaged rear wheel (OK laughs all round), however the calliper was positioned such
that there would have been a positive force pushing the spindle back into the dropout. A positive
engaging force so to speak. Obviously my fault not tightening the QR correctly- not weird science.
If we as riders make mistakes such as this, with respect, we should hold our hand up- not try and
place the blame elsewhere.
In summary I guess Pace are saying there can be a variable depending upon dropout design, calliper
design, OR design and correct fitting by the rider. But our view is that as long as all products are
designed correctly and the rider fits the OR and torques it up correctly the wheel will not
disengage.
Adrian Carter Pace Cycles Limited