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I recently discovered this horizontal line on my double walled aluminium rim (Triban road bike), pics attached, and was wondering if this was a crack or just a manufacturing artifact. Could anyone confirm if they've seen something like this? To me this looks too perfect a straight line to be a crack. Any ideas/opinions would be appreciated.

Many thanks JJ

left side - enter image description here

right side - enter image description here

Jyo Jena
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    Just for info, pinning is one way that the ends of the rim extrusion are joined. I think that typically, higher end alloy rims are welded, but it's also possible to make very high quality pinned rims with joints that aren't visible. First part of the linked answer talks about construction methods. Your rim is probably a more budget oriented rim, and it's possible you might feel a slight pulse as your brakes cross the joint. Otherwise, as already pointed out, there are no structural issues. https://bicycles.stackexchange.com/a/64832/38270 – Weiwen Ng Nov 11 '20 at 21:56

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That is the seam where the two edges of the rim were jointed. Cracks, as you have noted, do not form in such a perfectly uniform way.

As long as the edges remain closely butted together as they currently are, you are good to go.

jwh20
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The other answers and comments are excellent.
Adding a video on how rims are commonly made and a picture of the seam.

A double wall aluminum rim starts life as a straight piece of extruded aluminum.(Factory Tour: Velocity USA Bicycle Wheels)
The bar is bent to shape (about 3:51 in the video)and cut to length (4:13). The ends are joined together with a sleeve and epoxy (5:20)
Sleeved Joint Connection

enter image description here As Ralf points out since this seam is part of the manufacturing process both rims will have the seam.

If the rim maker does a good job the seam will be difficult to find. A variety of factors can make the seam more visible on one rim than another including manufacturing quality control and the type of stresses a rim experiences while riding. Knowing where to look makes finding the seam easier. As Michael says the seam is usually opposite the valve hole exactly between two spokes.

David D
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I have the same problem with my Bontrager Paradigm rim.

Can you tell me if this is normal or not?

enter image description here

Criggie
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Emadness
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  • Look on your other wheel and see if there's a seam in the same place, as suggested in other answers. Also, check for jaggedness. A seam joint will be straight. This looks not straight, but it's a photo and compression can make it hard to tell by remote. – Weiwen Ng May 16 '23 at 15:48
  • Thanks Yeah the two wheels have same pattern In same exact place – Emadness May 16 '23 at 16:44
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    As per OP, you have a straight line butted joint, not a crack. This post is a "Me too" and not an answer to the question. Please go read the [tour] because SE's Q&A format is a bit different to other chatty forum sites. – Criggie May 16 '23 at 18:25
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    I'm going to leave this here even though its NAA, because the photo is a good relevant example of another joint. – Criggie May 16 '23 at 20:55