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Carlton Reid on QR safety



 
 
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  #671  
Old February 17th 06, 06:14 PM posted to uk.rec.cycling,rec.bicycles.tech,alt.mountain-bike
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Default Carlton Reid on QR safety

On Fri, 17 Feb 2006 09:19:21 +0000, Tony Raven wrote:

Given how often lawyer lips have come up in this and the previous
threads on the topic, there is no chance that anyone has forgotten the
lawyer lips. The intent of laywer lips is not to provide axle retention
for disk brakes, it is to prevent people who don't know how to use QRs
from losing their front wheels.

Correct but by default it should prevent a QR from exiting the fork for
forces many times the highest calculated here for an ejection force.


Sadly not. British Standard 6102-1:1999 (which is based on ISO
4210:1996 but has advanced in some respects) requires wheel retention by
the QR mechanism of 2300N (517lbf) for 30 seconds, but with open QR the
lips have to withstand a load of just 100N (22.5lbf). [Section 9.4.4]



Mike

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  #672  
Old February 17th 06, 06:23 PM posted to uk.rec.cycling,rec.bicycles.tech,alt.mountain-bike
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Default Carlton Reid on QR safety


Tony Raven wrote:

I thought everyone here was was arguing against me that a loose QR was
not detectable by the rider until it got to the point the wheel was
ejected. Now you are trying to argue that a loose QR will be more than
detectable - it will loose you control of the bike. Which is it?


Be careful what you ascribe to "everyone." There can be differences of
opinion on such matters, even among people who agree that brakes should
not be trying to eject the front wheel from the dropouts.

FWIW, I don't know of anyone interested in bicycling safety issues who
feels it's fine to ride a bike with a loose QR, whose axle is held in
place only by the lawyer lips. If you feel such riding is fine, you'll
have very few members on your team.

Having a loose but
retained front wheel is not of itself unsafe.


Again, I think that's a VERY uncommon attitude. Can you find any
safety literature that agrees with you?

I've ridden that way with
disk brakes through my mistake a number of times although unlike many
here I pretty quickly knew something was wrong by the feel of the
steering and the knocking sound from the front wheel as the QR hit the
lawyers lips.


Under what conditions were you riding? It may be one thing to ride on
ordinary pavement under ordinary speeds with a loose QR (although,
again, I doubt you'll find anyone else who says so); but I suspect it's
quite another thing to be barrelling hell-bent-for-leather down a steep
rocky hillside with a loose QR. I don't do such riding, but I suspect
the sounds and sensations would be severely muddied by the general
chaos involved.

And of course, if you _were_ pounding your way down a super-steep,
rocky hill and felt something funny in your front wheel, what would you
do about it? Slam on the front brake even harder so you could stop to
inspect? Good luck!

- Frank Krygowski

  #673  
Old February 17th 06, 08:00 PM posted to uk.rec.cycling,rec.bicycles.tech,alt.mountain-bike
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Default Carlton Reid on QR safety

Mike Causer writes:

On Fri, 17 Feb 2006 09:19:21 +0000, Tony Raven wrote:

Given how often lawyer lips have come up in this and the previous
threads on the topic, there is no chance that anyone has forgotten
the lawyer lips. The intent of laywer lips is not to provide axle
retention for disk brakes, it is to prevent people who don't know
how to use QRs from losing their front wheels.

Correct but by default it should prevent a QR from exiting the fork
for forces many times the highest calculated here for an ejection
force.


Sadly not. British Standard 6102-1:1999 (which is based on ISO
4210:1996 but has advanced in some respects) requires wheel
retention by the QR mechanism of 2300N (517lbf) for 30 seconds, but
with open QR the lips have to withstand a load of just 100N
(22.5lbf). [Section 9.4.4]


Wow. Of course, those are the legal standards and not actual
measurements. Laywer lips do vary in design from just a couple of
small bumps at the tips of the dropouts to flanges that are almost
half the height of the QR nuts.

But do the math. Since the ejection force is applied to only one
dropout, the British Standard requirements are effectively that the QR
has to withstand a pullout force of 108.5 lbf and the lawyer lips only
11.25 lbf! I can't help but think that decent quality skewers and
forks would exceed this handily, hopefully anyway since even moderate
braking with a current design disk brake would create a force that
would exceed those numbers.
  #674  
Old February 17th 06, 11:38 PM posted to uk.rec.cycling,rec.bicycles.tech,alt.mountain-bike
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Default Carlton Reid on QR safety

In article , Tony Raven
wrote:

Luke wrote:


The primary device, unlike the secondary, does not simply retain, it
secures. The difference between these two functions is the difference
between having and losing control of the bike.


I thought everyone here was was arguing against me that a loose QR was
not detectable by the rider until it got to the point the wheel was
ejected. Now you are trying to argue that a loose QR will be more than
detectable - it will loose you control of the bike. Which is it?


That's an amusing contradiction. The secondary retention device,
'preferably' takes over in such a manner as to clearly inform that the
QRs have failed to secure the wheel (what if the Lawyers' Lips cite
client privilege, keeping mum?), which in of itself constitutes an
unsafe condition, but is not considered so until the secondary
retention system fails also.


Its a standard analysis for single fault tolerant safety critical
equipment: a single fault shall not create an unsafe condition nor go
undetected. Otherwise an undetected failure can continue obscured by
the secondary system until the secondary system fails and makes the
original fault visible in a potentially unsafe way. Having a loose but
retained front wheel is not of itself unsafe. I've ridden that way with
disk brakes through my mistake a number of times although unlike many
here I pretty quickly knew something was wrong by the feel of the
steering and the knocking sound from the front wheel as the QR hit the
lawyers lips.


Succinctly, here's my argument: What you consider 'wrong' constitutes
an unsafe condition to me; and what precipitates this condition (QR
failing) is characterized as failure. I disagree with your notion that
'a loose but retained front wheel is not of itself unsafe'.

That's all folks.
Luke






  #675  
Old March 1st 06, 01:38 AM posted to uk.rec.cycling,rec.bicycles.tech,alt.mountain-bike
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Default Carlton Reid on QR safety

I believe his point was that a reader may indeed be interested, but having
no added information, would not post uselessly.

I also find it interesting and would like the option to read or plonk as it
suits me. The idea of posting to merely say "I find this interesting" is
kinda lame.

Oh crap, I just did that.

"Andy H" wrote in message
...

Then do just that, you have no potential problems do you? Do you have the
statistics to hand?

Andy H




 




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