On Wednesday, October 17, 2018 at 12:22:49 PM UTC-7, Tosspot wrote:
On 10/17/18 2:45 PM, Tanguy Ortolo wrote:
Hello all,

A couple of months ago, I noticed my rear rim was worn out, with some
scratches I attributed to braking with sand or gravel on the pads. I
therefore replaced the wheel, and noticed that at some points, the old
ril was almost pierced!

Now, I am noticing without surprise that it would be wise to replace my
front rim as well. Although it has no obvious scratch like the read one
had, its braking surface has developped a concavity I think it did not
had at the beginning, so I suppose it is the result of successive
braking.

Does it sound normal for rims to wear out after about 30 or 40 thousand
kilometers?

Done a lot better than some of mine.

Now, since I am replacing it anyway, it will be a bit trickier than just
changing the wheel, because I have a hub dynamo. I will therefore have
to buy a new naked rim, (ligature the wheel spokes,) despoke the old
wheel, and respoke it with the new rim.

So, I have to choose a new rim, taking into account the following
parameters:
* rim dimensions and type: 622×19C
* number of spoke holes:

I there any other parameter I should take into account? Can I assume
that all 622 mm rims have spoke holes at the same distance from center?
Or in other words, that with keeping my hub and spokes, they will
correctly fit the new rim as long as it has the same diameter of 622 mm?

No. The effective rim diameter is very much dependent on rim model, so
you need to look it up. A quick start might be;

https://www.prowheelbuilder.com/spokelengthcalculator

So, pick a rim you like, get the ERD, then calculate the spoke length
for the ERD and hub you have.

All said and done, the tolerances are usually about 2mm, so don't sweat
it too much.

And assuming available ERDs are correct. You can get three or four different ERDs for some old rims, like Mavic MA2s -- from different sources, none directly from Mavic. http://velobase.com/ViewComponent.as...e-837eb8b21b0e I take the average. Then I try to find some modern rim with the same ERD -- which is not easy because everyone is trending to deep section or aero. You usually end up with some boat anchor from Sun or Alex -- or you pay through the nose for some modern clone. https://www.universalcycles.com/shop...4&category=139

I'm lucky to have Universal in town. They have a real rim inventory. Finding rims has become a lot more difficult over the last 30 years.

-- Jay Beattie.