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Old November 15th 17, 02:31 AM posted to
John B.[_3_]
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Posts: 3,967
Default Why do some forks and frames have brake rotor size limits?

On Tue, 14 Nov 2017 16:31:21 -0800, Joerg

On 2017-11-14 16:06, John B. wrote:
On Tue, 14 Nov 2017 12:43:41 -0800, Joerg

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

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?


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?

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.

Why ever so? After all you used adapters to mount your New! Big!
discs. Why can't you do exactly the same thing to mount the brakes on
the other side of the fork tube?

Requires total fork disassembly and aluminum welding, neither of which I
feel qualified to do or have the tools. Gets expensive if hired out.

Why welding? From what you wrote the forks have an existing mount for
the brakes. All you have to do is make a mounting that moves the
caliper to the front of the fork tube. A relatively simple design. See

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.


Sorry about that. Any Engineer worth is salt will recognize that using
larger discs may improve braking but no engineer worth is salt would
accept that as a fact with extensive testing.

When do you start reading more carefully before blurting out stuff that
makes no sense? I have underlined the salient section.

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.

What is next? The adapting of a motorcycle brake cylinder and lever to
a bicycle and the claim that it is better?

Possibly some day when I can retire some more. Today I had to fix
equipment in my electronics lab, needed to be able to do my job. That's
done. Now on to preparing the beer bottling for tomorrow. It'll be a
Belgian Saison and a Session Ale. Two other beers will be racked off to
secondary. Harvest trub for a bread, knead the dough, bake over wood
fire. Got to squeeze in a brew days as well and, of course, a riding
day. Then nursing home visits, preparing for continuing education
teaching, schedule ushers and greeters at church for the next quarter,
paint the deck underneath, and so on. See why there is only little time
left? :-)

Certainly. You simply considering making and consuming beer as more
important then cycling. Nothing wrong with that although some might
consider you a drunkard.

But spending the public's taxes on building bike-ways for drunks on
bicycles might be a bit more then most politicians might be willing to
underwrite :-)

John B.


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