Quoted message said:Alumina is the ceramic material most often used on bicycle rims.
* it's not pure alumina. it contains a number of ceramic elements which improve both wear resistance
and thermal conductivity - including titania and allegedly silicon carbide - but i can't confirm
this, unfortunately.
Quoted message said:Alumina (Al2 O3) has a _thermal_ conductivity about 16% that of aluminum
* a lot of rim alloys are 6061 or thereabouts. 6061 only has 70% of the thermal conductivity of pure
al, i.e. 167W/mK vs. 237W/mK.
* some alumina/silicon carbide ceramics have thermal conductivities in the range of 71-200W/mK,
potentially much better than 6061.
Quoted message said:There are any number of "innovations" put out by Mavic and others that show their disregard for
(or ignorance of) durability and performance. Changing from dual-sockets to single,
* there was a time when i would have agreed with you on this, but my experience is that it depends
on the application. ma3's are very strong & reliable - more so than open pro's in my view. making
these double eyelet would be an exercise in pointlessness.
hard anodizing,
* my experience of hard anodizing has been great. like ceramic, it's much less prone to the effects
of pad contamination and continues to offer a highly wear resistant braking surface in all
conditions. plain al rims with contaminated pads have been far worse at stopping me in the wet
than ceramic or hard anodized.
and for the record, i've read substantial verbiage on this group to the effect that anodizing causes
fatigue. in rim applications this is almost never the case from all the examples i've seen.
in extreme cases, cracked anodizing /can/ be a fatigue initiator, but this is not seen often in the
kind off applications we're talking about here. all kinds of fatigue-loaded components in planes,
cars, motorcycles and bicycles are anodized for corrosion resistance very successfully with no
adverse affects. one notable example has to be suspension forks. both bicycle and motorcycle forks
use [hard] anodized stantions for improved friction properties, corrosion and wear resistance, and
i've yet to see fatigue resulting from the anodizing alone - it's always been initiated by stone
strike damage or some other flaw.
unforunately, the cracking most commonly attributed to anodizing-initiated fatigue in bicycle rims -
pure circumferential cracking - is actually due to extrusion weaknesses in the alloy's
microstucture. if anyone wants to drag a certain french rim manufacturer over red hot coals for poor
q.c. in this department, be my guest, but don't blame it on the anodizing.
and machining
Quoted message said:sidewalls
* this is one that requires a real double-take when reading the faq! machines sidewalls offer
several benefits:
1. there is no "bed in" period for the pads - they fit right out of the box and provide full
braking power. i really notice the difference braking an unmachined rim on new pads vs. a
machined rim & new pads.
2. there is no potential for wheels locking at any bumps at the joint. i know some people swear this
is never an issue, but i can personally attest to owning a mavic cxp14 unmachined rim showing a
marked propensity to locking when under full braking - there is a bald patch on my tire where the
lock sets in at the same place every time.
3. rims are _not_ "machined with ridges to prevent squeal" or merely for appearance. 6061 is not
very friendly to normal lathe operations [the surface has a tendency to gouge and rip when the
machining off-cut fouls the tool]. the ridges on the machined surface are merely the result of
using a slightly convex diamond cutting tool which offers the best [read: cheapest, fastest,
cleanest] machining results for this application in a single pass.
