On 2017-11-16 09:24, Ned Mantei wrote:
On 16-11-17 14:43, AMuzi wrote:
On 11/16/2017 12:47 AM, Tosspot wrote:
Why do they have holes in them?

Car discs don't, motorbike discs don't, aircraft discs
don't. Why do bicycle discs have them?


Weight and also for swiping dirt and stuff. However, larger holes carry
a risk if you ride too close to another guy on a trail with finer
decomposed granite (we have a lot of that stuff). If a granule flies
into a rotor slot of the front wheel that can make for an "interesting
event".

Another downside of holes is the accumulation of "brake mousse" when you
ride through dense vegetation. It cakes up in there and then bakes. In
our area with yellow star-thistle and all that it can also stink. But
nothing that a Swiss Army knife can't fix. Just don't use it for cutting
sausage afterwards.


Many do have slots or holes. Typical low-end auto discs have a center
air channel. Our researcher discovered this by completely ignoring
normal maintenance:

http://www.yellowjersey.org/photosfr...t/NRCTDISC.JPG


As a maybe related question: Why do bike discs allow for so little wear?
The Shimano Ice-Tech discs are 1.8 mm thick, and need to replaced when
they wear to 1.5 mm. Would there be an issue with cooling if they were
thicker? Or, in the worst case, is this just a way for Shimano to sell
more replacements?


Buy rotors that are at least 1.9mm or thicker. On an MTB they last
around 5000 miles depending on turf, probably much longer on road bikes.
My first ones were 2.2mm and lasted even longer but couldn't find any
last month. It is also important to buy the better ones and not the
"resin pad only" rotors.

I sure wish they were 3mm or more.

--
Regards, Joerg

http://www.analogconsultants.com/