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Old November 14th 17, 01:03 AM posted to rec.bicycles.tech
Joerg[_2_]
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Posts: 4,699
Default Why do some forks and frames have brake rotor size limits?

On 2017-11-13 15:50, John B. wrote:
On Mon, 13 Nov 2017 10:06:52 -0800, Joerg
wrote:

On 2017-11-12 17:58, John B. wrote:
On Sun, 12 Nov 2017 09:37:54 -0800, Joerg
wrote:

On 2017-11-12 09:10, Frank Krygowski wrote:
On 11/11/2017 7:39 PM, Joerg wrote:

Yes, if 10" were more mainstream I'd probably have taken those but 8"
seems fine because I am not towing a brake-less trailer. A friend of
mine does though.

The extra cost is minimal. The adapters cost me $5.56 for both. The
rotors were around $23.70 each and the cost difference towards the
smaller versions will almost be made up by extended service life.

BTW there is a new bike shop in Placerville and one of the owners had
his MTB there the other day. 10" rotors on both wheels. He weighs less
than I do and said 8" was too iffy on some of his rides. These guys
know their stuff.

Let's look at the big picture. How do we decide which disc size is big
enough?


Big enough so they won't overheat on the longest descent on the usual
routes on a 105F day without overheating. Now that was simple.


I guess I'd have to ask "what is over heating"? You see a F1 car's
brakes work perfectly when they are red hot, around 1200 degrees (C),
in fact I understand that at ambient temperatures they are less
effective then when hot.

So, what is too hot?


Simple: When the point comes where the brake fades away, as happened to
an MTB rider in front of me at the last sharp turn down a long hill. If
he hadn't been a seasoned dirt bike rider he probably would have gone off.

[...]


It must be a problem with small discs as I've never had that problem
with my 700C rim brakes which operate quite similar to disc, i.e. a
rotating surface with pads that squeeze against both sides of the
rotating surface. Although, of course, my "discs" are about 27 inches
in diameter, not little puny 10 inch discs.


And they quite working in the rain. Mine don't.

Anyhow, ask people who had tire blow-outs when overheating the rim. On
the front that's not funny at all.



BTW, the most common excuse I hear from cyclists not to have made a
particular trip by bike is "It's got a flat right now". I have never
heard that from a motor vehicle user, ever.

But to be honest, I never heard a bicyclist say that, or a
motorcyclist say that, or a auto driver say that, or even a big 18
wheel trucker say that.

Is that something they say in Germany?



In California, Washington State, and so on. In Germany the standard
excuse is "Es ist gerade platt" which isn't logically correct but
common. "C'mon, let's fix it and ride" ... "Ahm, maybe next time".


Seriously? California cyclists can't fix a flat tire?



Most can but they won't. I'd hoped it had become clear by now that this
is a commonly used excuse, not an admittance of incompetence. They just
don't want to ride.

Although, I have met cyclists who could not fix a flat. One couldn't
even get the rear wheel out. He had an expensive new CF bike and was
clad in fancy Lycra. I couldn't believe it and then fixed it for him.
Oh, and the pump he had with him was totally useless for anything more
than a kid's tricycle.

There also are Californians who cart their bike to the LBS in their car,
drop it off to have a flat fixed and pick it up next day. No qualms at
all to drive 40mi and blow away almost two gallons of gasoline for that,
and more than a whole hour. No kidding. That dawned on me when I saw
"Flat fixing" on the standard price list at a bike shop. I asked the
owner whether that's a joke. "Oh no!"

--
Regards, Joerg

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