More on disk brakes and wheel ejection

[Rick Onanian]

On 1 Aug 2003 15:07:55 -0700, Spider <[email protected]> wrote:
> I own disk brakes, and use them often, on a mountain bike.

Often?

Do you sometimes ride that bike without using them?

> Spider
--
Rick Onanian

 

[James Annan]

John Rees wrote:
> <[email protected]> wrote in message news:[email protected]...

>>
>>We don't need no steenkin further research, as they say. All that is needed is to move the caliper
>>ahead of the fork, nothing more. In my estimation, this is the only reasonable solution that would
>>conclusively solve the problem.
>>
>>I cannot understand what all the hand wringing is about. Just do it! This is fretting at
>>its worst.
>
>
> Whether or not the calliper is moved on the forks there's a lot of expensive bikes out there that
> will not or cannot get retrofitted.

I'm sure you've mostly worked this out, but the reason why the manufacturers appear to be acting
like paralysed bunnies in headlights is that once their liability is established, they will be faced
with a massive recall problem and an indeterminate backlog of compensation claims.

Of course, by doing nothing, they increase the number of victims (and the number of forks in
circulation that will need to be altered). On top of this, they also risk not only merely paying
compensation but unlimited punitive damages on top of that for continuing to sell these products
with such an obvious flaw. But hey, what does that matter when there are peak summer sales figures
to enjoy? It is hard for them to keep up the pretence that they cannot create or understand the
problem when an interested (but originally sceptical) bike shop owner can reproduce the phenomenon
so easily and reliably just by riding to work a handful of times.

Some of you will have noticed that the CPSC issued a recall notice for some forks just this week.
This was some high-end carbon model with a theoretical cracking problem that has not resulted in any
incidents let alone injuries!

Meanwhile, back in the real world, there is a steady trickle of stories concerning serious injury as
riders misplace their front wheels on fast descents (all with disk brakes, of course). Several more
people have spent time in hospital in the last few weeks, including a couple of people who had
several days there due to serious head injuries.

James

 

[James Annan]

[email protected] wrote:
> Sheldon Brown writes:
>
>>What about changing the angle of the wheel slot in the fork ends to make it perpendicular to the
>>braking reaction force? This would seem a lot easier to do.
>
>
> I think we went through all that. As long as the braking forces are down and the wheel loads are
> up, the axle will move and the QR will unscrew. Therefore, changing the dropout slot orientation
> is only a bandaid and does not attack the underlying problem. The caliper must be in front so that
> its reaction forces are in the same direction as the wheel load forces. Only then will the
> reliable retention of the wheel be assured.

It's an important point that is worth highlighting. Some manufacturers are changing the slot angle
explicitly to address this problem (Planex X, Manitou Sherman?), and it seems clear to me that as
Jobst says, it's an improvement of sorts that still leaves an underlying problem unsolved.

James

 

[Tim McNamara]

In article <[email protected]>, [email protected] wrote:

> Tim McNamara <[email protected]> writes:
>
>
> > Well, this is still preliminary research and whilst it will undoubtedly put a bit of a rocket up
> > the proverbial of many fork manufacturers from our point of view as riders of disc equipped
> > bikes a little perspective is in order. Whilst it is looking like there seems to be an emerging
> > problem the incidences of actual accidents that can be attributed to skewers undoing are clearly
> > very small. Common sense coupled with a routine of skewer checking whilst out on the trails will
> > most likely be enough to limit the problem to a very small risk. In short there is nothing here
> > that suggests mountain bikers with disc brakes should panic and revert back to V-brakes. As they
> > say in the science world, more research is needed.

Whoops, wait a minute, I didn't write this! This was a quote from the article referenced in my post.

 

[Tim McNamara]

In article <[email protected]>,
"John Rees" <[email protected]> wrote:

> Well, I didn't see the rest of the discussion. Your post stands as the first in the thread on my
> newsreader. The post you responded to and quoted was undated, makes it tough for me to located the
> original thread..

I was the original poster and let me clarify a few things. First, the title of this thread is the
title I used for my first post, but that was several weeks ago (and it was promptly ignored by most
of the loud voices trying to shout down james Annan). The odds are it's spooled off your news server
some time ago, but you can find the original post at Google.

You can also find a lot of other posts on this very topic- search for James Annan as the author and
you'll find them.

 

[Tim McNamara]

In article <[email protected]>, [email protected]
(Spider) wrote:

> Why? AFAIK, there has been *no* experiemental research done on this system. If there are published
> articles, could you please post a link? I am very interested.

I did. The very first article in this thread was by me posted July 17th, prompted by seeing
publication of experimental research that confirms there *is* a problem with current disk brake fork
design. The doubting Thomases promptly ignored it.

You can find it at Google. You can also find the reference article at:

http://www.singletrackworld.com/article.php?sid=1063

 

[Spider]

Tim McNamara <[email protected]> wrote in message
news:<[email protected]>...
> In article <[email protected]>, [email protected]
> (Spider) wrote:
>
> > Why? AFAIK, there has been *no* experiemental research done on this system. If there are
> > published articles, could you please post a link? I am very interested.
>
> I did.

No, you didn't. The German firm gave STW some preliminary results, but I could not find a single,
published article on this - and by that I mean an article that describes the materials and
conditions under which the preliminary result was discovered. IOW, a scientific article, published
in a peer-reviewed journal.

> The very first article in this thread was by me posted July 17th, prompted by seeing publication
> of experimental research that confirms there *is* a problem with current disk brake fork design.
> The doubting Thomases promptly ignored it.

No, that article *did not* contain published work that describes the experiment.

I apologize for not being clear on what I meant by "published article." The world of science
attaches something wholly different to this term than the layman, and it behooves me to make
that clear.

Again, my apologies.

Spider

 

[Maki]

In article <[email protected]>, Dave Lehnen
<[email protected]> wrote:

> > That would require re-desining the calipers, n'es-ce pas?
> >
> <snip>
>
> If the caliper is moved from the rear of the left fork to the front of the right fork, the
> hydraulic line or cable would still exit in about the correct (upwards) direction.

You have to modify both the fork and the caliper mounts, so it requires redesigning the whole
system. It makes non sense to revamp the caliper when the real problem is the hub-fork interface.

--
Fact of life #15: Heads bleed, walls don't.

 

[Dave Lehnen]

Maki wrote:
> In article <[email protected]>, Dave Lehnen
> <[email protected]> wrote:
>
>
>>>That would require re-desining the calipers, n'es-ce pas?
>>>
>>
>><snip>
>>
>>If the caliper is moved from the rear of the left fork to the front of the right fork, the
>>hydraulic line or cable would still exit in about the correct (upwards) direction.
>
>
> You have to modify both the fork and the caliper mounts, so it requires redesigning the whole
> system. It makes non sense to revamp the caliper when the real problem is the hub-fork interface.
>

For most calipers, you only need to modify the fork, as suggested above. An exception would be
calipers like the Shimano XT, with different diameter leading and trailing pistons.

Dave Lehnen

 

[Maki]

In article <[email protected]>, Dave Lehnen
<[email protected]> wrote:

> For most calipers, you only need to modify the fork, as suggested above. An exception would be
> calipers like the Shimano XT, with different diameter leading and trailing pistons.

Oh, sorry. I missed the "from left to right part". Yes, in theory it will work, but I'm not sure all
the calipers are made to brake backwards. The pads may very well be more supported in one way than
the other. And you still need to replace the fork, usually the most expensive part. I don't
understand what's wrong with improved skewers.

--
Fact of life #15: Heads bleed, walls don't.

 

[Rick Onanian]

On Wed, 06 Aug 2003 19:31:42 GMT, Maki <[email protected]> wrote:
> I don't understand what's wrong with improved skewers.

I saw skewers the other day that have a lock against unintentional loosening. They have a
spring-loaded button you must press to release or turn/loosen them.

Suppose these would help?

--
Rick Onanian

 

[Maki]

In article <[email protected]>, Rick Onanian <[email protected]> wrote:

> I saw skewers the other day that have a lock against unintentional loosening. They have a
> spring-loaded button you must press to release or turn/loosen them.
>
> Suppose these would help?

IMHO yes. Experience shows that QRs that exceed by far the current iso standards exist, so it
is clearly possible to make them strong enough. It remains the problem of sloppy users that
dont' tighteen enough, so the QR can unscrew. With the lock this is gone too. However the ISO
standard should be updated and require a specific logo on the skewer so that one can
distinguish the good ones.

--
Fact of life #15: Heads bleed, walls don't.

 

[Tim McNamara]

In article <[email protected]>, Maki <[email protected]> wrote:

> In article <[email protected]>, Rick Onanian <[email protected]> wrote:
>
> > I saw skewers the other day that have a lock against unintentional loosening. They have a
> > spring-loaded button you must press to release or turn/loosen them.
> >
> > Suppose these would help?
>
> IMHO yes. Experience shows that QRs that exceed by far the current iso standards exist, so it is
> clearly possible to make them strong enough. It remains the problem of sloppy users that dont'
> tighteen enough, so the QR can unscrew.

Not so sure that this last sentence is really accurate.

 

[James Annan]

Maki <[email protected]> wrote in message
news:<[email protected]>...

> IMHO yes. Experience shows that QRs that exceed by far the current iso standards exist, so it is
> clearly possible to make them strong enough.

That's a non sequitur. 'Exceed by far' still may not achieve a sensible margin of safety with
current designs.

> It remains the problem of sloppy users that dont' tighteen enough, so the QR can unscrew. With the
> lock this is gone too. However the ISO standard should be updated and require a specific logo on
> the skewer so that one can distinguish the good ones.

Did you have a specific definition of 'good' in mind?

James

 

[Maki]

In article <[email protected]>, [email protected] (James
Annan) wrote:

> > IMHO yes. Experience shows that QRs that exceed by far the current iso standards exist, so it is
> > clearly possible to make them strong enough.
>
> That's a non sequitur. 'Exceed by far' still may not achieve a sensible margin of safety with
> current designs.

James, it's you that linked the QR tests on your website. When the standard asked for 500N some
reached 4000N or so. The current generation is probaly much better. Testing is needed of course, but
the aneddoctal evidence that you report shows that in some way (almost?) anybody having troubles was
able to solve them either changing QRs or thightening them more.

At worst, if the margin of safety in case of misuse is really insufficient one can redesign the
hubs, no need to rework the fork and/or the calipers. Think about the system used on rear wheels on
most motorcycles and give some steroids to your skewer so that it becomes an M9 axle: that would
allow much bigger tension without the fear of snapping. Also, the fact that the axle can then be
extracted will permit to close the dropout in future forks for better safety, while still being both
quick and backwards compatible.

> > However the ISO standard should be updated and require a specific logo on the skewer so that one
> > can distinguish the good ones.
>
> Did you have a specific definition of 'good' in mind?

"good" = "able to withstand the disk-generated forces" What I meant is that updating the standards
so that they require, say, 6000N is not useful if I can't distinguish what skewers meet the new
parameters. A specific logo on the QR will solve this.

As I said in a previous thread I never liked QRs on MTBs, so if you can make them disappear I'm
happy, but I dont' think that throwing away existing forks to save the current QRs is a good idea.
Calipers are fine where they are, the weak link is the wheel/hub interface.

--
Fact of life #15: Heads bleed, walls don't.

 

[James Annan]

Maki wrote:

> James, it's you that linked the QR tests on your website. When the standard asked for 500N some
> reached 4000N or so. The current generation is probaly much better.

I think that's a misinterpretation. The standard had already been updated to 2300N rather than the
earlier 500N, and I do not believe the skewers changed either before or since (I don't even know for
which, if any, countries, the ISO standard is a legally-adopted requirement). The forcing can be
easily shown to be in the region of the 4000N that the best skewers achieved (remember that is only
2000N per dropout, and the disc force is focussed mainly on one side).

> At worst, if the margin of safety in case of misuse is really insufficient

The problem is that the margin of safety is already nonexistent in the case of CORRECT use. You
can't simply say that with hindsight, the skewer should have been tighter, if it has already been
correctly adjusted according to the manufacturer's instructions.

> one can redesign the hubs, no need to rework the fork and/or the calipers. Think about the system
> used on rear wheels on most motorcycles and give some steroids to your skewer so that it becomes
> an M9 axle: that would allow much bigger tension without the fear of snapping. Also, the fact that
> the axle can then be extracted will permit to close the dropout in future forks for better safety,
> while still being both quick and backwards compatible.

This 'backwards compatibility' appears to require a new front wheel (hub with larger hole for fatter
skewer) - is this correct?

> What I meant is that updating the standards so that they require, say, 6000N is not useful if I
> can't distinguish what skewers meet the new parameters. A specific logo on the QR will solve this.

It's also no good unless you have a simple method of ensuring that your skewer will reliably hold
6000N when used under real conditions, ie in the presence of a bit of mud by a tired MTBer with cold
hands. I personally doubt very much whether this approach is a viable one, but we'll have to see
what the manufacturers try...

James

 

[Tim McNamara]

In article <[email protected]>, Maki <[email protected]> wrote:

> Calipers are fine where they are, the weak link is the wheel/hub interface.

No, the problem is that the fork design is flawed. Not the wheel/hub interface, not the QRs, etc.
The fork puts the caliper in exactly the right place to push the wheel out of the dropout. Annan has
demonstrated this quite clearly, yet people like yourself insist on shilly-shallying around looking
for some kludge to try to overcome a significant design flaw.

Why is this so difficult to comprehend? People's lives quite literally depend on this. The design
should be corrected to prevent the wheel from being ejected from the dropout even if the skewer is
left open, if it unscrews, if it breaks under tension, or whatever. The wheel should NEVER be forced
out of the dropout as a result of braking!

 

[Jobst Brandt]

Maki Tartamillo writes:

>> We don't need no steenkin further research, as they say. All that is needed is to move the
>> caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution
>> that would conclusively solve the problem.

> Redesigning the QR so that it cannot unscrew is easier, cheaper, and backwards compatible.

Could you outline how such a device would work and how it would prevent the axle from moving up and
down alternately with braking and normal load, the mechanism by which QR's are unscrewed?

As long as the attachment is a "dropout", having braking forces trying to pull the wheel downward is
a threatening condition that makes a reasonably cautious rider worry about how tight is tight
enough. The less skilled or forgetful riders could fare worse. With the caliper ahead of the fork,
all these concerns are removed.

Jobst Brandt [email protected] Palo Alto CA

 

[Jobst Brandt]

Rick Onanian writes:

>> I'm not sure what you are envisioning. You would then have to flex the fork legs outward to fit
>> the axle, and most forks are too stiff to be flexed easily by that amount.

> No, you'd just pull the skewer right out of the wheel.

When you propose that, I take it you are not capturing the axle in the dropout, as is customary with
a QR, but are expecting the QR to hold the wheel alone. In that case, the skewer would need to be
about 10mm in diameter as axles are now. What sort of axle for mounting bearings, do you have in
mind? I see these various suggestions as incomplete designs and not practical solutions.

>> This doesn't solve the problem anyway. There will be some play when the axle is fit into its
>> hole. It would still get pushed up and down to the extent of that play by braking and bump
>> forces. The play wouldn't result in wheel ejection, but it still isn't good design.

> Well, I'm no engineer, but an engineer could probably come up with something like my idea but
> better. Or, just make the dropout holes the same size as the hole in the hub -- the hub doesn't
> have any play up and down on the skewer.

If you are not an engineer then you probably should consider axles in holes without clearance a
press fit and after some use a loose fit. Since I cannot visualize what you have in mind, I suspect
your method has not yet been thought out to practical completion.

Jobst Brandt [email protected] Palo Alto CA

 

[Jobst Brandt]

James Annan writes:

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

>>> We don't need no steenkin further research, as they say. All that is needed is to move the
>>> caliper ahead of the fork, nothing more. In my estimation, this is the only reasonable solution
>>> that would conclusively solve the problem.

>>> I cannot understand what all the hand wringing is about. Just do it! This is fretting at its
>>> worst.

>> Whether or not the caliper is moved on the forks there's a lot of expensive bikes out there that
>> will not or cannot get retrofitted.

> I'm sure you've mostly worked this out, but the reason why the manufacturers appear to be acting
> like paralyzed bunnies in headlights is that once their liability is established, they will be
> faced with a massive recall problem and an indeterminate backlog of compensation claims.

I don't think it is as bad as you describe. If manufacturers acted now, modified their forks and
recalled existing models, a solid defense would be that the current design was general practice for
all bicycles and that no one found fault with it until a large user field had established with a
large variety of rider demands and operator skills. This would demonstrate a good faith response to
a belated discovery that should be without major criticism. This would be different, had there been
some manufacturers who placed calipers ahead of the fork and to whom one could point as proof of a
known hazard.

What is done as retrofit is up to the industry. I see making a fail safe "bandaid" that may not be
graceful or stylish, but it could be made safe at the expense of clean elegance. I even envisage a
retention means that would prevent the wheel from ejecting but without trying to prevent loosening,
so that essentially a "buzzer" noticeable (looseness) would alert the rider to tighten the QR.

Jobst Brandt [email protected] Palo Alto CA