Mark writes Seems the bike industry decided to refer to anything hard-grey anodized as "heat-treated". Often the same rim was sold both ways, with the anodized one called heat-treated when the anodizing was the only difference. Once again referring to my April 1984 issue of Bike Tech (sad git!) I find an article by Mario Emiliani (no relation) headed Anodized Rims are More Rigid. There follows various equations and a conclusion "So for the rim used in these calulations its rigidity is 21% greater than if it was not hard anodized". Surprising eh, if true. I should have mentioned that the first article I referred to was by Chris Juden who is the technical editor of the CTC magazine. His articles are great although obviously he concentrates on touring bikes. Prior to writing the article he had been employed as a design engineer for the Mistral rims division of TI Sturmey Archer. Ray Green, Brighton, England
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