Re: "Actually you are the first person to bring up this issue"

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Tim McNamara writes:

>>> Name calling doesn't change the facts, BTW. Neither does your
>>> anger nor your emotional reasoning. Everybody that has disk
>>> brakes may just have been hoodwinked by the companies that made
>>> them- those are the people you should be challenging.

>> Should not the criticism be leveled at the fork manufacturers and
>> not the brake manufacturers?

> IMHO both, since they are equal parts of the system. The brake is
> designed by its maker to be mounted behind the fork leg, and the
> fork is designed to put it there by its maker. Both are equal
> contributors to the problem.

> I don't know but do suspect that changing the dropout design might
> be the easier solution, and I don't know but do suspect that
> changing the location of the brake would be the better solution.

If you consider forks without offset at the dropout end, as they are
commonly made today, where offset is achieved at the fork crown, No
change other than placing the mounting lugs for the disc brake caliper
on the front side is required. I think the same caliper would be
adequate for most brands with the distance between caliper and fork
leg remaining as it is today. This requires a new fork strut anyway.

Changing the dropout is not a reasonable option because the dropout
would need to face upward, which would release the wheel on normal
wheel loads, while reversing loads of rider and brake force, being
opposite, could still cause QR loosening. The dropout should be
loaded in the same direction at all times as it is with rim brakes.

That stress reversals cause unanticipated failures was evident in the
old Shimano short splined hollow BB axles. Riders who descended
standing, right foot forward, had crank loosening and spline failures
as I predicted. We had a similar thread to this one on that issue as
well as one on the progressive ratio Campagnolo Delta brake. Both
products are no longer made for practical and safety reasons.

How long will it take to get the disc caliper ahead of the fork leg?

Jobst Brandt
jobst.brandt@stanfordalumni.org

James Annan writes:

>> If you consider forks without offset at the dropout end, as they
>> are commonly made today, where offset is achieved at the fork
>> crown, No change other than placing the mounting lugs for the disc
>> brake caliper on the front side is required. I think the same
>> caliper would be adequate for most brands with the distance between
>> caliper and fork leg remaining as it is today. This requires a new
>> fork strut anyway.

> It might even be possible to simply swap the left and right fork
> lowers. Sometimes one sees bikes where the forks have been
> installed backwards... usually on ebay.

>> How long will it take to get the disc caliper ahead of the fork leg?

> I wouldn't be surprised to see different wheel attachment instead.
> There are already various quick(ish) release 20mm systems that seem
> little more trouble than a QR with retention lips. That can also be
> sold as an upgrade rather than merely a bug-fix. And you get to buy
> a new shiny hub too!

Well that won't do as I already mentioned. The reversing load from
braking and bouncing on the road makes anything but a conical "lug
nut" ineffective to reliably prevent loosening.

Let's get the caliper in the right place!

Jobst Brandt
jobst.brandt@stanfordalumni.org

jobst.brandt@stanfordalumni.org writes:

> Tim McNamara writes:
>
>>>> Name calling doesn't change the facts, BTW. Neither does your
>>>> anger nor your emotional reasoning. Everybody that has disk
>>>> brakes may just have been hoodwinked by the companies that made
>>>> them- those are the people you should be challenging.
>
>>> Should not the criticism be leveled at the fork manufacturers and
>>> not the brake manufacturers?
>
>> IMHO both, since they are equal parts of the system. The brake is
>> designed by its maker to be mounted behind the fork leg, and the
>> fork is designed to put it there by its maker. Both are equal
>> contributors to the problem.
>
>> I don't know but do suspect that changing the dropout design might
>> be the easier solution, and I don't know but do suspect that
>> changing the location of the brake would be the better solution.
>
> If you consider forks witqhout offset at the dropout end, as they are
> commonly made today, where offset is achieved at the fork crown, No
> change other than placing the mounting lugs for the disc brake caliper
> on the front side is required. I think the same caliper would be
> adequate for most brands with the distance between caliper and fork
> leg remaining as it is today. This requires a new fork strut anyway.
>
> Changing the dropout is not a reasonable option because the dropout
> would need to face upward, which would release the wheel on normal
> wheel loads, while reversing loads of rider and brake force, being
> opposite, could still cause QR loosening. The dropout should be
> loaded in the same direction at all times as it is with rim brakes.

I was thinking of facing the open end of the dropouts forward, so
that the normal load would be directed into the end of the fork leg,
and the lower "jaw" of the dropout would constrain the braking
force. This wouldn't be suitable?

Tim McNamara wrote:

> jobst.brandt@stanfordalumni.org writes:

>>Changing the dropout is not a reasonable option because the dropout
>>would need to face upward, which would release the wheel on normal
>>wheel loads, while reversing loads of rider and brake force, being
>>opposite, could still cause QR loosening. The dropout should be
>>loaded in the same direction at all times as it is with rim brakes.
>
>
> I was thinking of facing the open end of the dropouts forward, so
> that the normal load would be directed into the end of the fork leg,
> and the lower "jaw" of the dropout would constrain the braking
> force. This wouldn't be suitable?

It would still leave the alternating up/down forcing. Bolts don't need
to have a massively elongated slot to loosen in. Probably it would
reduce the magnitude of the problem, but there is a simple solution that
eliminates it.

James

Tim McNamara writes:

>>> I don't know but do suspect that changing the dropout design might
>>> be the easier solution, and I don't know but do suspect that
>>> changing the location of the brake would be the better solution.

>> If you consider forks without offset at the dropout end, as they
>> are commonly made today, where offset is achieved at the fork
>> crown, No change other than placing the mounting lugs for the disc
>> brake caliper on the front side is required. I think the same
>> caliper would be adequate for most brands with the distance between
>> caliper and fork leg remaining as it is today. This requires a new
>> fork strut anyway.

>> Changing the dropout is not a reasonable option because the dropout
>> would need to face upward, which would release the wheel on normal
>> wheel loads, while reversing loads of rider and brake force, being
>> opposite, could still cause QR loosening. The dropout should be
>> loaded in the same direction at all times as it is with rim brakes.

> I was thinking of facing the open end of the dropouts forward, so
> that the normal load would be directed into the end of the fork leg,
> and the lower "jaw" of the dropout would constrain the braking
> force. This wouldn't be suitable?

As I said, I believe that as long as there is a large reversing load
on that joint it has the ability to loosen a threaded fastener. Now
is not the time to introduce half baked solutions, especially if it
requires changing the fork anyway.

Besides, I like QR's and they are not in contention with any solution
other than positioning the caliper ahead of the fork.

Jobst Brandt
jobst.brandt@stanfordalumni.org

jobst.brandt@stanfordalumni.org wrote:
>
>
> Let's get the caliper in the right place!
>

Right place for what? It might reverse the ejection force into a holding in
force but OTOH the caliper is out front where it is much more susceptible to
damage and to getting the mounting tabs bent/strained by hitting things. The
mounts would also be under tension under braking, rather than compression
which has an increased chance of failure. Specialized have already had a
recall for mounting tab failures. Don't simply replace one problem with
another and think through all the failure modes of a proposed solution before
implementing it - Design Control 101.

Tony

Tony Raven writes:

>>>> If you consider forks without offset at the dropout end, as they
>>>> are commonly made today, where offset is achieved at the fork
>>>> crown, No change other than placing the mounting lugs for the
>>>> disc brake caliper on the front side is required. I think the
>>>> same caliper would be adequate for most brands with the distance
>>>> between caliper and fork leg remaining as it is today. This
>>>> requires a new fork strut anyway.

>>> It might even be possible to simply swap the left and right fork
>>> lowers. Sometimes one sees bikes where the forks have been
>>> installed backwards... usually on eBay.

>>>> How long will it take to get the disc caliper ahead of the fork leg?

>>> I wouldn't be surprised to see different wheel attachment instead.
>>> There are already various quick(ish) release 20mm systems that
>>> seem little more trouble than a QR with retention lips. That can
>>> also be sold as an upgrade rather than merely a bug-fix. And you
>>> get to buy a new shiny hub too!

>> Well that won't do as I already mentioned. The reversing load from
>> braking and bouncing on the road makes anything but a conical "lug
>> nut" ineffective to reliably prevent loosening.

>> Let's get the caliper in the right place!

> Right place for what?

The right place to resolve the hazards that have been under discussion
in this thread for more than 500 replies.

> It might reverse the ejection force into a holding in force but OTOH
> the caliper is out front where it is much more susceptible to damage
> and to getting the mounting tabs bent/strained by hitting things.

Yes, and the moon may yet be made of green cheese. This is grasping
at straws to obscure the issue when all else fails. What sort of
damage do you foresee for a metal brake caliper that is far behind the
leading edge of an adjacent wheel? This sounds like the bicycle is
being tossed into a rock crusher. Ejection forces from a rear mounted
caliper are real and undeniable, bending parts of the fork "from
hitting things" is unreal conjecture as is apparent from aluminum
parts of suspension forks that are not full of scrapes and gouges on
their front side "from hitting things".

> The mounts would also be under tension under braking, rather than
> compression which has an increased chance of failure. Specialized
> have already had a recall for mounting tab failures. Don't simply
> replace one problem with another and think through all the failure
> modes of a proposed solution before implementing it - Design Control
> 101.

There is nothing wrong with tension. If it were we couldn't ride
spoked wheels that have plenty of tension. In fact, no matter how you
make it, the bicycle (and n=most machines) are full of tension and
compression stresses. That is what bending is.

Jobst Brandt
jobst.brandt@stanfordalumni.org

Tony Raven wrote:


> Specialized have already had a
> recall for mounting tab failures.

When?

If you mean the recent recall of bikes with too large a rotor installed,
there were NO failures and no evidence that there ever would be any
failures. The problem was merely that the combination had not been
properly checked.

Puts the current situation regarding disks and QRs into context, don't
you think?

James

James Annan wrote:
> Tony Raven wrote:
>
>
>> Specialized have already had a
>> recall for mounting tab failures.
>
> When?
>
> If you mean the recent recall of bikes with too large a rotor installed,
> there were NO failures and no evidence that there ever would be any
> failures. The problem was merely that the combination had not been
> properly checked.
>
> Puts the current situation regarding disks and QRs into context, don't
> you think?
>
> James

I should choose my words more carefully. I should have said that "Specialized
have already had a recall for _potential_ mounting tab failures"

The CPSC release said:

Hazard: During heavy braking, the brake tabs on the front forks could break
off, possibly causing a loss of control and fall from the bicycle.

Tony