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Old November 14th 17, 09:43 PM posted to rec.bicycles.tech
Joerg[_2_]
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Default Why do some forks and frames have brake rotor size limits?

On 2017-11-13 19:04, Frank Krygowski wrote:
On 11/13/2017 7:09 PM, Joerg wrote:
On 2017-11-13 15:53, John B. wrote:
On Mon, 13 Nov 2017 10:10:05 -0800, Joerg
wrote:

On 2017-11-12 17:46, John B. wrote:

[...]


As an aside, I just measured the front discs on my wife's Honda Jazz
(I think it is called a "Fit"in the U.S.) and to my horror I find that
they are only 240mm (9.4") in diameter. As the nominal weight of the
car is about 1100 Kg (2400lb), as opposed to (probably) an all up
weight of less then 250 lbs for a bicycle, it is obvious that they
can't possibly be large enough to be safe. And Horrors, there isn't
any room to fit larger :-(


Of course, you didn't bother to measure the rotor thickness and didn't
notice the fact that it is rather solid.

Whatever are you talking about? Does the thickness of the disc matter?



sigh

I thought you were an engineer. No, I am not going to answer this
because it should be easy to figure that out for yourself.


If so why are bicycle (and motorcycle) disc such puny little things
hardly thicker then a piece of paper?



Have you ever wondered why a motorcycle rotor weighs over a pound?

https://i2.wp.com/www.yamahar3racing...9/IMG_4199.jpg


Now _that_ would be the dream for the front wheel of my MTB.


So why aren't you using it? I thought you were an engineer.


For the umpteenth time:

1. I don't have a lathe and other tools.

2. It requires adapting the fork mounts to a motorcycle caliper and the
handle has to come from a Yamaha.

3. I just don't have that much time right now. For example, this
afternoon I get to modify an RF amp from my EMC set-up where the
rechargeable battery size has become unobtanium. Not my favorite job but
as John Wayne said "Man's got to do what man's got to do".

4. I just converted the MTB to 8" rotors for both wheels. Any engineer
woth his salt will recognize when good enough is good enough. I shall
try that out extensively but I think that'll do the trick.

BTW, #2 wouldn't be so bad because that would eliminate the dreaded
(messy) burping procedure. Bike brake systems have no extra reservoir
tank for whatever reason.

--
Regards, Joerg

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