Crack in aluminium rim?

Question

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 - 
right side -

jwh20 · Accepted Answer

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.

David D · Answer

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

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.

Crack in aluminium rim?

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