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.
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.
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.
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" <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.
"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.
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.
1. The fork is specifically called "freeride (that is what FR means) and Marzocchi clearly state on their website that this fork is compatible 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.
James
Freeride means different things to different people, but frankly anybody who need 8" rotors also needs 20mm axles anyway. As noted in the thread, Marzocchi have their physics backwards anyway. The usual reason for not fitting big rotors is excessive loadings on the caliper mounting tabs.
Kinky Cowboy*
*Batteries not included May contain traces of nuts Your milage may vary
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.
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 !!!
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
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.
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
The limit of braking torque is called an endo. 1" steerer tubes have been handling that for years without breaking. Bigger rotors can't change this limit, which can be reached with pretty much any kind of common bicycle brake.
Aside from fashion (probably the major factor), increasing rotor diameter on a bicycle reduces lever force for a given amount of braking, which is handy on a DH/FR bike where you need to do lots of hard braking without getting carpal tunnel syndrome, and increases the heat dissipation capability of the brake system, which might reduce fade where that's a problem. Kinky Cowboy*
*Batteries not included May contain traces of nuts Your milage may vary
> 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
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.
