Bicycle Mechanics - What does this mean?
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09-14-05, 02:43 PM
" pinned but well aligned rim seam"
anybody got any insight? Do they extrude the metal, bend it, and hold it together with safety pins? Well aligned safety pins? Please, enlighten. Thanks!
09-14-05, 03:10 PM
You're close. Bicycle rims are made from long, straight metal extrusions. The extrusions are bent into a coil, cut and flattened to make hoops. More expensive rims are welded and the brakeing surfaces are machined to make them nice and smooth. Cheaper rims just have metal dowels inserted into holes in the extrusion to hold the seam together.
There isn't much stress on the rim joint. Even if there was, the tire beads in tension would hold the rim joint together. The biggest disadvantage of the pinned rim joint goes back to when the extrusion was flattened to transform a coil into a series of hoops. If it wasn't perfectly flattened (and they never are) it leaves little steps in the brakeing surface on each side of the rim at the joint. Generally a few hunderd miles of normal road use will smooth the joint to the point that it's hardly noticeable.
09-14-05, 03:14 PM
OK, that makes sense. Thanks!
I've only ever built wheels with sun rims, and they always had an annoying *ping* when I was trying to get the vertical true, due to a slight ridge at the seam. Can I assume that these rims were pinned?
09-15-05, 03:26 AM
Yeah, they're pinned together. I just use a small precision file and give the raised edge at the seam a couple of strokes and it's usually perfect after that.
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