Building a disc brake wheel with rim brake rims

Tech Tech Help
1

Any reason not to, other than the vestigial brake track? It’s a carbon rim, so not super obvious.

2

Why not? Especially if you got a good deal on them. They’ll be fine.

3

Seconded. :ok_hand:

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4

I agree with the others: mechanically it will be perfectly sound.

However, I do think rims designed for rim brakes are necessarily constrained by that, and so disc brake rims might have some minor advantages:

  • A rim brake rim needs to be slightly beefier to cope with the braking forces, and maintain strength as the brake track gets worn to some degree. A disc rim can therefore be slightly lighter, on a “like-for-like” basis (although this may be offset or even outweighed by the extra width of a disc brake rim; see below).
  • I understand manufacturers of carbon disc brake rims often use lower temperature resins, as they do not need to cope with the heat produced by the brakes. The claim is that this reduces brittleness, increasing impact resistance and vibration damping (paraphrased from Hunt’s website).
  • A rim brake rim will necessarily be narrow (to fit within brake calipers) and the brake tracks will be flat. A rim designed for disc brakes can be wider, and can be curved anywhere (e.g. a nice smooth toroidal shape). So overall better aerodynamics, especially with wider tyres.

Whether any of those things matter enough to bother you is another question!

5

Aren’t there spoke count concern difference between rim and disc brake rims? I think that’s only an issue if your rim brake rim is very low spoke count?

6

That’s what I’ve heard when talking to a wheel builder about this a while back when I had more rim brake wheels gathering dust in my garage. He didn’t recommend it because of lower spoke count on many road wheels. I think it was a HED Ardennes rim brake.

7

Should be no problem so long as the spoke counts are sufficient (24h or more) and they aren’t drilled for some weird lacing pattern (pretty unusual).

Do make sure you select a disc appropriate lacing if you build them up. Don’t radially laced the front wheel for example.

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8

I’ve got an interesting one. Tubular rim brake carbon rim (38mm deep), drilled 24 hole. Laced to a 32h disc front hub with 16 spokes 2x on the left (caliper) side and 8 spokes 1x on the right side. Because of the difference in flange offset and height from one side to the other, the tensions are close between the two sides. The wheel has been through a decade of CX and never given me any issues.

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