Does "hard anodizing" make rims stronger?
There are several kinds of dark coatings sold on rims. Each suggests that
added strength is achieved by this surface treatment while in fact no useful
effects other than aesthetic results are achieved. The colored rims just
cost more as do the cosmetically anodized ones. The hard anodized rims
do not get stronger even though they have a hard crust. The anodized crust
is brittle and porous and crazes around spoke holes when the sockets are
riveted into the rim. These cracks grow and ultimately cause break-outs
if the wheel is subjected to moderate loads over time.
There is substantial data on this and many shops that build many wheels,
can tell you that for instance, no MA-2 rims have cracked while MA-40 rims
fail often. These are otherwise identical rims.
Hard anodizing is also a thermal and electrical insulator. Because heat
is generated in the brake pads and not the rim, braking energy must cross
the interface to be dissipated in the rim. Anodizing, although relatively
thin, impedes this heat transfer and reduces braking efficiency by overheating
the brake pad surfaces. Fortunately, in wet weather, road grit wears off
the sidewall anodizing and leaves a messy looking rim with better braking.
Anodizing has nothing to do with heat treatment and does not strengthen
rims. To make up for that, it costs more.
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