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strange rims at supermarket

Old 07-02-04, 02:44 PM
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cart@@n
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strange rims at supermarket

Hello guys,

Looking for a future beater bike, i was at supermarket looking at what would be classified "wallmart bikes" at U.S. Then i noticed that the aluminium rims of some bikes had a seam at a point, like it was a straight piece, turned into a circle, then glued? - there was no visible weld it was just held in place somehow.

I never noticed this thing before, so i went to look the rims of higer quality bikes, and it was there too, but the "top quality" bike bikes at the place had "seamless" rims.

But what got my attention, was the first bike i saw (it was the cheaper), and the "seam" was not so well made, so there was a bit of metal left away from the rim surface, and i think it would catch the brake pads every time they come in contact, loking the well always at the same place, and ripping off some bits of the pad´s surface. There was some happy peolple taking those bikes.

Are those "seam" rims normal at a quality bike?
Should i worry with them?
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Old 07-02-04, 03:09 PM
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Originally Posted by cart@@n
Are those "seam" rims normal at a quality bike?
Should i worry with them?
They're quite normal and I would not worry about them. Many quality racing rims have seams. Up until a few yrs ago all rims had seams.
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Old 07-02-04, 03:33 PM
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All bicycle rims have a seam.

When they make a bicycle rim they usually start with an aluminum extrusion that is long enough to make several rims. The extrusion is formed into a coil, the coil is cut and the newly formed circles are flattened. From this point, less expensive rims have pins inserted into the voids in the extrusion and the pins are all that holds the joint together. More expensive rims are welded at the joint. A punch forms the spoke and valve holes.
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Old 07-03-04, 11:07 AM
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Pins vs welds do not make the difference between a cheap rim or not. Up intill just a few years ago ALL racing rims were pinned and some still are!! And the logic behind the two is insane!!! Weld is cheaper than pinning thus most have gone that way, just as welding frames is cheaper than lugging them. Here is some info:

Newsgroups: rec.bicycles.tech
From: jbrandt@hpl.hp.com (Jobst Brandt)
Subject: Re: Machined rims, was Re: rim cracks - advice needed
Date: Mon, 1 Apr 1996 20:36:03 GMT

Jason Kangas writes:

> You may be overlooking the fact that Mavic first started machining their rims after they welded the joint. The welded joint has to be one of the strongest methods for joining a rim. The machining of the rim was designed to remove the excess weld material and create a consistent braking track. Also, by anodizing the rim first and then
removing the slippery process from the side of the rim, certain cosmetic effects are possible without the normal uneven look of partially worn off anodizing.<

ANSWER:
I'm not overlooking that at all. The bicycle industry is run by people as unclear on technical matters as the average wreck.bike experts who expound upon things about which they know little. That rims do not require any fastening at the joint, completely escapes them. They could not have done an analysis of this joint or they would recognize the foolishness that welded joints are. It's an old "idee fixe" that wants a continuous perfect circle without joint. Fiamme made rims that all had a ding in the joint because some well meaning person thought the rims would separate if they weren't riveted. The riveting machine deformed the profile on both sides of the joint. This, even though Fiamme had earlier made a whole series of rims that were smooth and had no rivets, similar to Mavic's butt joined rims, rims that formerly could be pulled apart although I almost suspect Mavic now glues them. The joint is held together by
about 1000 pounds force when the spokes of a wheel are tightened. That they anodize rims is proof that no one is technically at home there. Materials science literature has ample publications concerning the fatigue susceptibility of aluminum parts coated with brittle porous hard coatings (anodizing). The aircraft industry, long ago, made these discoveries but the bicycle trade, that is mostly driven by fashion and managed by non technical people, must go through the long arduous process of first hand experience.

The subject of tire treads is classic in that it is driven entirely by marketing considerations. The scientific method is not employed here. Similarly cranks are being offered in forms that have no relation to their stresses. Most NC machined cranks have minimal torsional strength and do not address the principal failure modes, but they sure look techie! I think the "Don't lubricate the spindle press fit" admonition screams of failure understand cause and effect.

Jobst Brandt <jbrandt@hpl.hp.com>
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Old 07-03-04, 01:20 PM
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Wow... someone just got owned by the above post.
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Old 07-03-04, 06:37 PM
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Originally Posted by froze
Pins vs welds do not make the difference between a cheap rim or not. Up intill just a few years ago ALL racing rims were pinned and some still are!! And the logic behind the two is insane!!! Weld is cheaper than pinning thus most have gone that way
I don't think so, Froze. When I look up rims in a catalogue, all of the least expensive rims are pinned and only the more expensive ones are welded. You can argue whether welding is necessary, but that doesn't change the fact of catalogue prices.
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