J
jim beam
Guest
[email protected] wrote:
> On Nov 9, 10:10 am, Tim McNamara <[email protected]> wrote:
>> [email protected] wrote:
>>
>> <snip much verbiage>
>>
>>> On Nov 7, 11:26 pm, jim beam <[email protected]> wrote:
>>>> read the thread again. i explained how it works back on 11/1 in a
>>>> reply to "_".
>>> You didn't explain how it works. You explained how it could work,
>>> but your observations are not sufficient to support your explanation.
>>> Your observation of changing relative brake pad distances may be
>>> explained by either the orientation of the brake pads (which you
>>> refuse to accept) or an out of plane orientation of the second pivot
>>> (which the rest of us refuse to accept). The tie breaker is fore-aft
>>> pad translation. One arm of the dual pivot caliper cannot twist.
>> If that was the case, then brake squeal would not happen. The caliper
>> arm can flex in at least two ways; the longer the distance from the
>> pivot to the brake pad, the greater this is an issue.
>>
>>> It's rotating about the mounting bolt, with one degree of freedom.
>> That's assuming a perfect bearing, which doesn't exist. There are at
>> least three degrees of freedom there. One is large, the other two are
>> (or should be) very small.
>>
>>> If there is something special about that second pivot, which
>>> differentiates the caliper as front or rear by making the arm twist
>>> one way or another, then the pad attached to it will be moving fore
>>> and aft relative to the other pad as the caliper opens and closes.
>>> Since you have such a great geometry teacher, this should be obvious.
>>> This is not happening though, and nobody has claimed to have
>>> observed it happening, including yourself.
>> Grab a brake lever and squeeze tight. Now rock the bike back and forth.
>> Do the brake pads move relative to the fork blades or seatstays? On
>> my bikes I can detect a very small fore and aft movement by placing my
>> finger between the brake and the frame. There is no visual movement of
>> the pads vis a vis the frame on my bikes, except on one with
>> cantilever brakes- there's much more play in the pivots as well as twice
>> as many pivots. On all my bikes the movement is more pronounced for the
>> front brake, which is probably due to fork flex. Note that the forces
>> in this little experiment are much smaller than actual braking forces
>> when riding. In real life, my guess (and it is a guess) is that frame
>> flex would account for more undesirable movement of the brake pads than
>> odd motions in the pivot.
>>
>> Strain gauges on the brake caliper arms might answer the question.
>> Anybody here got some? Maybe a project for Fogel Labs!
>
> All very good points, but the ways in which a caliper deflects under
> load aren't the issue here. There's a claim here that there's an arm
> twisting under no load that's a result of a design feature. There
> has been no credible evidence to support this, only optical tricks.
>
er, you said:
"If there is something special about that second pivot, which
differentiates the caliper as front or rear by making the arm twist one
way or another, then the pad attached to it will be moving fore and aft
relative to the other pad as the caliper opens and closes."
and my pics just so happen to show precisely that. but now you're
back-tracking saying it's some kind of deception? that's ridiculous.
> On Nov 9, 10:10 am, Tim McNamara <[email protected]> wrote:
>> [email protected] wrote:
>>
>> <snip much verbiage>
>>
>>> On Nov 7, 11:26 pm, jim beam <[email protected]> wrote:
>>>> read the thread again. i explained how it works back on 11/1 in a
>>>> reply to "_".
>>> You didn't explain how it works. You explained how it could work,
>>> but your observations are not sufficient to support your explanation.
>>> Your observation of changing relative brake pad distances may be
>>> explained by either the orientation of the brake pads (which you
>>> refuse to accept) or an out of plane orientation of the second pivot
>>> (which the rest of us refuse to accept). The tie breaker is fore-aft
>>> pad translation. One arm of the dual pivot caliper cannot twist.
>> If that was the case, then brake squeal would not happen. The caliper
>> arm can flex in at least two ways; the longer the distance from the
>> pivot to the brake pad, the greater this is an issue.
>>
>>> It's rotating about the mounting bolt, with one degree of freedom.
>> That's assuming a perfect bearing, which doesn't exist. There are at
>> least three degrees of freedom there. One is large, the other two are
>> (or should be) very small.
>>
>>> If there is something special about that second pivot, which
>>> differentiates the caliper as front or rear by making the arm twist
>>> one way or another, then the pad attached to it will be moving fore
>>> and aft relative to the other pad as the caliper opens and closes.
>>> Since you have such a great geometry teacher, this should be obvious.
>>> This is not happening though, and nobody has claimed to have
>>> observed it happening, including yourself.
>> Grab a brake lever and squeeze tight. Now rock the bike back and forth.
>> Do the brake pads move relative to the fork blades or seatstays? On
>> my bikes I can detect a very small fore and aft movement by placing my
>> finger between the brake and the frame. There is no visual movement of
>> the pads vis a vis the frame on my bikes, except on one with
>> cantilever brakes- there's much more play in the pivots as well as twice
>> as many pivots. On all my bikes the movement is more pronounced for the
>> front brake, which is probably due to fork flex. Note that the forces
>> in this little experiment are much smaller than actual braking forces
>> when riding. In real life, my guess (and it is a guess) is that frame
>> flex would account for more undesirable movement of the brake pads than
>> odd motions in the pivot.
>>
>> Strain gauges on the brake caliper arms might answer the question.
>> Anybody here got some? Maybe a project for Fogel Labs!
>
> All very good points, but the ways in which a caliper deflects under
> load aren't the issue here. There's a claim here that there's an arm
> twisting under no load that's a result of a design feature. There
> has been no credible evidence to support this, only optical tricks.
>
er, you said:
"If there is something special about that second pivot, which
differentiates the caliper as front or rear by making the arm twist one
way or another, then the pad attached to it will be moving fore and aft
relative to the other pad as the caliper opens and closes."
and my pics just so happen to show precisely that. but now you're
back-tracking saying it's some kind of deception? that's ridiculous.
