On 17-10-18 16:36, 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?

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: 36.

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?

Cheers,


I don't think rims have ever lasted 30,000 km for me. They become
concave from braking, and need to be replaced when the thickness is 1 mm
or less. Disastrous accidents can happen if the rim isn't replaced soon
enough.

Many rims have some sort of wear indicator, for example tiny holes that
disappear when the rim wears down enough. For this maybe check the
website of the company that produced the rim.

When looking for a new rim check tables with the ERD (effective rim
diameter) of various rims (google "rim erd database"). I would try for a
new rim such that the ERD is within 1 mm or so.

Jobst said that spokes should ≈always be reused, and that his were still
fine after about 100,000 miles. I have followed Jobst's advice for about
15 or 20 years, and never had a spoke break.

Concerning "despoking", in his book "The Bicycle Wheel", Jobst Brandt
said to move the spokes one at a time from the old to the new rim,
starting next to the valve holes. This works for me. Pay attention to
how the spoke holes are arranged on the rim: Often they alternate
between one side of the rim or the other, and you want the same
orientation on the new rim.

And then comes truing the wheel so that it's round, centered between the
hub locknuts, and the spokes have more or less even tension. I have no
routine with this, and even with a truing stand, a dish tool to check
for centering, and a tensiometer, it takes me about 3 hours to get the
wheel close enough. People who do this often probably need less than
half an hour. It helps if you have a good sense of pitch, so that you
can judge relative tension by the tone you hear when plucking a spoke.

I would suggest first reading up on this and/or watching some videos.

Ned