Marzocchi comes clean

James Annan said:

Well, cleanER, anyway. This was forwarded to me from another front wheel
victim recently. I have cut out some personal details but the reply is
quoted in full:

--------------

Quoted message said:

Dear Customer
in reply to your technical question

(is an 8" rotor compatible with Z1 FR fork)

Quoted message said:

It will definitely fit onto the fork. It is recommended that an 8" rotor
is not used on a standard axle fork because the forces exerted on the
wheel can potentially pull the axle out of the dropouts. So, it will
physically fit, but it is not recommended for aggressive riding.

Best Regards,
Marzocchi Staff

--------------

Is 8" big or small for a disc? Maybe I need to think through it some more,
but visualizing the problem, my first impression is that smaller discs
should create larger ejection forces than larger discs.

Andrew Lee

You have it backwards.
Larger disc equals more leverage.

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
news:[email hidden]...

Quoted message said:

James Annan said:

Well, cleanER, anyway. This was forwarded to me from another front wheel
victim recently. I have cut out some personal details but the reply is
quoted in full:

--------------

Quoted message said:

Dear Customer
in reply to your technical question

(is an 8" rotor compatible with Z1 FR fork)

Quoted message said:

It will definitely fit onto the fork. It is recommended that an 8"

rotor

Quoted message said:

Quoted message said:

Quoted message said:

is not used on a standard axle fork because the forces exerted on the
wheel can potentially pull the axle out of the dropouts. So, it will
physically fit, but it is not recommended for aggressive riding.

Best Regards,
Marzocchi Staff

--------------

Is 8" big or small for a disc? Maybe I need to think through it some

more,

Quoted message said:

but visualizing the problem, my first impression is that smaller discs
should create larger ejection forces than larger discs.

Andrew Lee

jw said:

Quoted message said:

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
Is 8" big or small for a disc? Maybe I need to think through it some
more,
but visualizing the problem, my first impression is that smaller discs
should create larger ejection forces than larger discs.

Andrew Lee

You have it backwards.
Larger disc equals more leverage.

A larger disc has more leverage for braking, but smaller ejection forces
than a smaller disc. A rim brake is the largest disc and produces the least
amount of force at the axle, though the dropouts are orientated
perpendicular to the force anyway.

Here's how I'm visualizing it. Grab the rim directly behind the axle and
pull up on the rim with the brake applied. The brake pads are between your
hand and the axle. The pad/disc interface is the fulcrum that is levering
the axle down. The closer the fulcrum is to the axle (smaller disc), the
more leverage there is against the axle. You can also visualize pushing the
part of the rim directly in front of the axle downwards to lever the axle
down pivoting against the pad/disc interface behind the axle. Same
conclusion.

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
news:[email hidden]...

Quoted message said:

Here's how I'm visualizing it. Grab the rim directly behind the axle and
pull up on the rim with the brake applied. The brake pads are between

your

Quoted message said:

hand and the axle. The pad/disc interface is the fulcrum that is levering
the axle down. The closer the fulcrum is to the axle (smaller disc), the
more leverage there is against the axle. You can also visualize pushing

the

Quoted message said:

part of the rim directly in front of the axle downwards to lever the axle
down pivoting against the pad/disc interface behind the axle. Same
conclusion.

Under braking think of the tyre contact patch as being the fixed end of a
lever <1> with the other end of the lever being the axle which has a force
applied it (mass of moving bike & rider). Now the pad/disc interface
becomes the fulcrum, the greater the disc dia the further away the fulcrum
is from the force applied to the lever (axle).
<1> Which effectively means any part of the tyres circumference.

Pete

Peter B said:

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
news:[email hidden]...

Quoted message said:

Here's how I'm visualizing it. Grab the rim directly behind the axle and
pull up on the rim with the brake applied. The brake pads are between

your

Quoted message said:

hand and the axle. The pad/disc interface is the fulcrum that is
levering
the axle down. The closer the fulcrum is to the axle (smaller disc), the
more leverage there is against the axle. You can also visualize pushing

the

Quoted message said:

part of the rim directly in front of the axle downwards to lever the axle
down pivoting against the pad/disc interface behind the axle. Same
conclusion.

Under braking think of the tyre contact patch as being the fixed end of a
lever <1> with the other end of the lever being the axle which has a
force
applied it (mass of moving bike & rider). Now the pad/disc interface
becomes the fulcrum, the greater the disc dia the further away the fulcrum
is from the force applied to the lever (axle).
<1> Which effectively means any part of the tyres circumference.

Pete

I agree with your last sentence about "any part of the tyres circumference"
.. That's why I was able to give my visualization examples from the front
and rear of the wheel. The mass of the moving rider and bike is the force
that I am simulating when I say pull up on the rim from behind the axle or
push down on the rim from in front of the axle. I can visualize it the way
you describe too, but I still conclude that opposite, that the smaller disc
produces a greater ejection force. Look at your lever again and vary the
fulcrum distance closer and and farther away from the rear of the axle.
When the brake is applied, the L-shaped lever goes from the tire/ground to
the pad/disc fulcrum to the axle and prys the axle down from the dropouts.
The shorter the disc to axle distance compared to the disc/pad to
tire/ground distance, the greater the force.

in message <[email hidden]>, "Andrew Lee"

whatsupandrewathotmaildotcom ('') said:

James Annan said:

Well, cleanER, anyway. This was forwarded to me from another front
wheel victim recently. I have cut out some personal details but the
reply is quoted in full:

--------------

Quoted message said:

Dear Customer
in reply to your technical question

(is an 8" rotor compatible with Z1 FR fork)

Quoted message said:

It will definitely fit onto the fork. It is recommended that an 8"
rotor is not used on a standard axle fork because the forces
exerted on the wheel can potentially pull the axle out of the
dropouts. So, it will physically fit, but it is not recommended for
aggressive riding.

Best Regards,
Marzocchi Staff

--------------

Is 8" big or small for a disc?

Relatively large, but increasingly seen on downhill and freeride bikes.
Most cycling disks are still nominally 6"; however, there's a certain
fashion element in the move to 8" I think.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Hobbit ringleader gives Sauron One in the Eye.

Andrew Lee whatsupandrewathotmaildotcom said:

James Annan said:

Well, cleanER, anyway. This was forwarded to me from another front
wheel victim recently. I have cut out some personal details but the
reply is quoted in full:

--------------

Quoted message said:

Dear Customer
in reply to your technical question

(is an 8" rotor compatible with Z1 FR fork)

Quoted message said:

It will definitely fit onto the fork. It is recommended that an 8"
rotor is not used on a standard axle fork because the forces
exerted on the wheel can potentially pull the axle out of the
dropouts. So, it will physically fit, but it is not recommended for
aggressive riding.

Best Regards,
Marzocchi Staff

--------------

Is 8" big or small for a disc? Maybe I need to think through it some
more, but visualizing the problem, my first impression is that
smaller discs should create larger ejection forces than larger discs.

Andrew Lee

Physics 101: Torque = force x distance, the larger disc has the
larger distance from the axle.

--
- Zilla
Cary, NC
(Remove XSPAM)

Zilla says...

Quoted message said:

Physics 101: Torque = force x distance, the larger disc has the
larger distance from the axle.

You should have waited for Physics 102. The point may or may not be
valid depending on the position of the caliper.

Quoted message said:

The shorter the disc to axle distance compared to the disc/pad to
tire/ground distance, the greater the force.

tau = r x F

--
Phil, Squid-in-Training

"Phil, Squid-in-Training" <[email hidden]> wrote in
message news:[email hidden]...

Quoted message said:

Quoted message said:

The shorter the disc to axle distance compared to the disc/pad to
tire/ground distance, the greater the force.

tau = r x F

Look, I already answered this in another thread.

V = IR.

cheers,
clive

Zilla vaguely muttered something like ...

Quoted message said:

Andrew Lee whatsupandrewathotmaildotcom said:

James Annan said:

Well, cleanER, anyway. This was forwarded to me from another front
wheel victim recently. I have cut out some personal details but the
reply is quoted in full:

--------------
> Dear Customer
> in reply to your technical question

(is an 8" rotor compatible with Z1 FR fork)

> It will definitely fit onto the fork. It is recommended that an 8"
> rotor is not used on a standard axle fork because the forces
> exerted on the wheel can potentially pull the axle out of the
> dropouts. So, it will physically fit, but it is not recommended for
> aggressive riding.
>
> Best Regards,
> Marzocchi Staff
--------------

Is 8" big or small for a disc? Maybe I need to think through it some
more, but visualizing the problem, my first impression is that
smaller discs should create larger ejection forces than larger discs.

Andrew Lee

Physics 101: Torque = force x distance, the larger disc has the
larger distance from the axle.

But has the same force (brakes and rider/bicycle weight) acting upon it at
that distance, so develops less force at the axle than a smaller rotor.

--
Paul ...
http://www.4x4prejudice.org/index.php
"A [censored] is a [censored], no matter what mode of transport they're using."
(8(|) Homer Rules !!!

Paul - censored said:

Quoted message said:

Quoted message said:

Is 8" big or small for a disc? Maybe I need to think through it some
more, but visualizing the problem, my first impression is that
smaller discs should create larger ejection forces than larger discs.

Andrew Lee

Physics 101: Torque = force x distance, the larger disc has the
larger distance from the axle.

But has the same force (brakes and rider/bicycle weight) acting upon it at
that distance, so develops less force at the axle than a smaller rotor.

But with the caliper in another position the direction of the force
might have changed for the worse

--
---
Marten

James Annan said:

1. The fork is specifically called "freeride (that is what FR means)

and

Quoted message said:

Marzocchi clearly state on their website that this fork is compatible

Quoted message said:

with 8" rotors:
2. The writer acknowledges that the front wheel may detach, but
Marzocchi are still apparently continuing to sell the product to
customers without mentioning this fault.

Only a complete idiot runs an 8" rotor on a standard QR fork. Lesser
idiots run an 8" rotor on QR20 single crown forks. Single crown forks
can't handle the torque safely, which should be common knowledge by
now.

JD

Clive George said:

"Phil, Squid-in-Training" <[email hidden]>
wrote in message news:[email hidden]...

Quoted message said:

Quoted message said:

The shorter the disc to axle distance compared to the disc/pad to
tire/ground distance, the greater the force.

tau = r x F

Look, I already answered this in another thread.

V = IR.

The answer is 5 coulombs.

--
Phil, Squid-in-Training

Paul - censored said:

Zilla vaguely muttered something like ...

Quoted message said:

Andrew Lee whatsupandrewathotmaildotcom said:

"James Annan" <[email hidden]> wrote:

> Well, cleanER, anyway. This was forwarded to me from another front
> wheel victim recently. I have cut out some personal details but the
> reply is quoted in full:
>
> --------------
>> Dear Customer
>> in reply to your technical question
>
> (is an 8" rotor compatible with Z1 FR fork)
>
>> It will definitely fit onto the fork. It is recommended that an 8"
>> rotor is not used on a standard axle fork because the forces
>> exerted on the wheel can potentially pull the axle out of the
>> dropouts. So, it will physically fit, but it is not recommended
>> for aggressive riding.
>>
>> Best Regards,
>> Marzocchi Staff
> --------------

Is 8" big or small for a disc? Maybe I need to think through it
some more, but visualizing the problem, my first impression is that
smaller discs should create larger ejection forces than larger
discs. Andrew Lee

Physics 101: Torque = force x distance, the larger disc has the
larger distance from the axle.

But has the same force (brakes and rider/bicycle weight) acting upon
it at that distance, so develops less force at the axle than a
smaller rotor.

But you're stopping faster.
--
Phil, Squid-in-Training

in message <[email hidden]>, Phil,

Squid-in-Training (') said:

Paul - censored said:

Zilla vaguely muttered something like ...

Quoted message said:

Andrew Lee <whatsupandrewathotmaildotcom> wrote:
> "James Annan" <[email hidden]> wrote:
>
>> Well, cleanER, anyway. This was forwarded to me from another front
>> wheel victim recently. I have cut out some personal details but
>> the reply is quoted in full:
>>
>> --------------
>>
>> (is an 8" rotor compatible with Z1 FR fork)
>>
>>> It will definitely fit onto the fork. It is recommended that an
>>> 8" rotor is not used on a standard axle fork because the forces
>>> exerted on the wheel can potentially pull the axle out of the
>>> dropouts. So, it will physically fit, but it is not recommended
>>> for aggressive riding.
>
> Is 8" big or small for a disc? Maybe I need to think through it
> some more, but visualizing the problem, my first impression is that
> smaller discs should create larger ejection forces than larger
> discs. Andrew Lee

Physics 101: Torque = force x distance, the larger disc has the
larger distance from the axle.

But has the same force (brakes and rider/bicycle weight) acting upon
it at that distance, so develops less force at the axle than a
smaller rotor.

But you're stopping faster.

No. The limit on stopping is still the point at which you unweight the
back wheel. You can't stop a bike faster than that. The argument for
eight inch rotors, in so far as it is not just fashion, is that they
have more cooling surface area and can thus dissipate heat faster,
leading to less brake fade on very long fast downhill courses.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Woz: 'All the best people in life seem to like LINUX.'
;; <URL:http://www.woz.org/woz/cresponses/response03.html>

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
news:[email hidden]...

Quoted message said:

Is 8" big or small for a disc? Maybe I need to think through

it some more,

Quoted message said:

but visualizing the problem, my first impression is that

smaller discs

Quoted message said:

should create larger ejection forces than larger discs.

Andrew Lee

This web page explains the problem with 8" rotors on standard
forks:

http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
http://makeashorterlink.com/?T538360A4

Alien Rider said:

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote in message
news:[email hidden]...

Quoted message said:

Is 8" big or small for a disc? Maybe I need to think through

it some more,

Quoted message said:

but visualizing the problem, my first impression is that

smaller discs

Quoted message said:

should create larger ejection forces than larger discs.

Andrew Lee

This web page explains the problem with 8" rotors on standard
forks:

http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html
http://makeashorterlink.com/?T538360A4

You have the math right in front of you and you still get it backwards?

Marzocchi obviously wasn't coming clean because they obviously don't
understand the problem at all.

Simon Brooke said:

in message <[email hidden]>, Phil,

Squid-in-Training (') said:

Paul - censored said:

Zilla vaguely muttered something like ...
> Andrew Lee <whatsupandrewathotmaildotcom> wrote:
>> "James Annan" <[email hidden]> wrote:
>>
>>> Well, cleanER, anyway. This was forwarded to me from another
>>> front wheel victim recently. I have cut out some personal
>>> details but the reply is quoted in full:
>>>
>>> --------------
>>>
>>> (is an 8" rotor compatible with Z1 FR fork)
>>>
>>>> It will definitely fit onto the fork. It is recommended that an
>>>> 8" rotor is not used on a standard axle fork because the forces
>>>> exerted on the wheel can potentially pull the axle out of the
>>>> dropouts. So, it will physically fit, but it is not recommended
>>>> for aggressive riding.
>>
>> Is 8" big or small for a disc? Maybe I need to think through it
>> some more, but visualizing the problem, my first impression is
>> that smaller discs should create larger ejection forces than
>> larger discs. Andrew Lee
>
> Physics 101: Torque = force x distance, the larger disc has the
> larger distance from the axle.

But has the same force (brakes and rider/bicycle weight) acting upon
it at that distance, so develops less force at the axle than a
smaller rotor.

But you're stopping faster.

No. The limit on stopping is still the point at which you unweight the
back wheel. You can't stop a bike faster than that. The argument for
eight inch rotors, in so far as it is not just fashion, is that they
have more cooling surface area and can thus dissipate heat faster,
leading to less brake fade on very long fast downhill courses.

Ugh. If you're going downhill on a mountain bike, there are lots of bumps.
These bumps increase the normal force of the ground on the tire/fork. When
you're tired, and your lever effort is, say, X newtons, then you can hold a
higher braking force with an 8-inch rotor than if you're using 6-inch rotor.

When you have bumps, the normal force increases at what I think is a huge
magnitude, one so high that you won't lift the rear wheel (because there's
no time to get it up), and the tire won't skid, either (because there's such
a big normal force to the terrain/bump). Therefore, the braking force and
the corresponding downward dropout-busting force is higher.

With the 6-inch rotor, the bump is likely to cause the rotor to slip more
between the pads than if one was using 8-inch rotors.

Why do so many keep thinking that these issues happen on dry, flat pavement?
(including Cannondale)

--
Phil, Squid-in-Training