J
Jules
Guest
Jose Rizal <_@_._> wrote in message news:<[email protected]>...
>
> > I don't really see what there is to 'prove' here, there is nothing new about this other than the
> > realisation that the necessary and sufficient preconditions apply in this situation.
>
> "Can" apply in this situation. I never said there was anything new in the concept of threaded
> systems loosening under cyclic motion, only that it still remains to be shown that this is what
> happens in QR systems in the situation you describe. What is to be proved is whether this
> mechanism can be made to happen in QRs/disc brake systems, thereby eliminating subjective data
> from anecdotes.
>
> This mechanism is straightforward: loosening will occur if there is enough cycles of movement, or
> large enough amplitudes of movement, or both. There is no magic random factor which will affect
> this. The process of this mechanism happening, however, will cause effects which will serve as
> warnings and which are not mentioned in the bulk of your anecdotal data. Hence the doubt whether
> the anecdotal data is reliable enough.
See the thread on singletrack world, posted after James had realised that QRs can unscrew.
http://www.singletrackworld.com/forum/read.php?f=2&i=341365&t=341361#reply_341365
In case you cannot be bothered to read it all here is a summary: In the thread, on which people
posted over the course of 3 days...
14 people reported first hand front wheel loosening or front wheel loss on disk brake plus QR
equipped bikes, riding under repeated sharp braking conditions.
There were, in addition, 6 second hand reports (although one person reported seeing it happen 'many
times' to different people - his report is just counted as one of the 6 here)
Of these 20 cases, 11 were wheel loosening, and several people reported repeated loosening - eg.
every 2 weeks.
Of the 20 cases, 9 were wheel losses, resulting in face plants, usually on one of the tough classic
UK mountain descents (Iron Keld, Helvellyn, Cumberland Clough...).
Of the 20 cases, 3 resulted in serious injuries - 1 paralysis from the chest down, 1 intensive care
and 1 with a large amount of facial scarring, including loss of his left nostril! (eww!)
How many people read singletrack on those 3 days? What fraction of these use disk brakes plus QRs?
How many of these ride in the conditions that require repeated braking that will quickly loosen the
QR? Don't know what these numbers are, but it would seem reasonable that of order 1% of disk brake
plus QR release users are likely to have such problems. That's a large number of people in the
whole world!
Then there are, of course, all these people who subsequently have piped up to say that it has not
happened to them. But looked at in terms of 1% failure being quite large, the number of these happy
people unfortunately does not seem as high as one would hope.
In order for your QR to never fail you need to be in the happy position of having a skewer with
knurling, combined with fork dropouts that are neither to soft nor too hard, such that the skewer
makes little divots in the dropout. The knurls sit in the divots and make it much harder for the QR
to unscrew. It also helps if you do not ride long, steep rocky descents (which, of course, most
riders do not - perhaps no Americans ever do?). If your QR does not unscrew, because you have this
combination of a good QR and a good dropout, then, assuming you have retention lips on your dropout
you will have no problems. Hopefully this situation describes the vast majority of riders, but it
appears that little attention has been paid by the industry to make sure that this is the case.
jules
>
> > I don't really see what there is to 'prove' here, there is nothing new about this other than the
> > realisation that the necessary and sufficient preconditions apply in this situation.
>
> "Can" apply in this situation. I never said there was anything new in the concept of threaded
> systems loosening under cyclic motion, only that it still remains to be shown that this is what
> happens in QR systems in the situation you describe. What is to be proved is whether this
> mechanism can be made to happen in QRs/disc brake systems, thereby eliminating subjective data
> from anecdotes.
>
> This mechanism is straightforward: loosening will occur if there is enough cycles of movement, or
> large enough amplitudes of movement, or both. There is no magic random factor which will affect
> this. The process of this mechanism happening, however, will cause effects which will serve as
> warnings and which are not mentioned in the bulk of your anecdotal data. Hence the doubt whether
> the anecdotal data is reliable enough.
See the thread on singletrack world, posted after James had realised that QRs can unscrew.
http://www.singletrackworld.com/forum/read.php?f=2&i=341365&t=341361#reply_341365
In case you cannot be bothered to read it all here is a summary: In the thread, on which people
posted over the course of 3 days...
14 people reported first hand front wheel loosening or front wheel loss on disk brake plus QR
equipped bikes, riding under repeated sharp braking conditions.
There were, in addition, 6 second hand reports (although one person reported seeing it happen 'many
times' to different people - his report is just counted as one of the 6 here)
Of these 20 cases, 11 were wheel loosening, and several people reported repeated loosening - eg.
every 2 weeks.
Of the 20 cases, 9 were wheel losses, resulting in face plants, usually on one of the tough classic
UK mountain descents (Iron Keld, Helvellyn, Cumberland Clough...).
Of the 20 cases, 3 resulted in serious injuries - 1 paralysis from the chest down, 1 intensive care
and 1 with a large amount of facial scarring, including loss of his left nostril! (eww!)
How many people read singletrack on those 3 days? What fraction of these use disk brakes plus QRs?
How many of these ride in the conditions that require repeated braking that will quickly loosen the
QR? Don't know what these numbers are, but it would seem reasonable that of order 1% of disk brake
plus QR release users are likely to have such problems. That's a large number of people in the
whole world!
Then there are, of course, all these people who subsequently have piped up to say that it has not
happened to them. But looked at in terms of 1% failure being quite large, the number of these happy
people unfortunately does not seem as high as one would hope.
In order for your QR to never fail you need to be in the happy position of having a skewer with
knurling, combined with fork dropouts that are neither to soft nor too hard, such that the skewer
makes little divots in the dropout. The knurls sit in the divots and make it much harder for the QR
to unscrew. It also helps if you do not ride long, steep rocky descents (which, of course, most
riders do not - perhaps no Americans ever do?). If your QR does not unscrew, because you have this
combination of a good QR and a good dropout, then, assuming you have retention lips on your dropout
you will have no problems. Hopefully this situation describes the vast majority of riders, but it
appears that little attention has been paid by the industry to make sure that this is the case.
jules
with little additional
