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Suppose I have a disk-compatible hub and frame, but want build a wheel based around a very specific touring rim, which is labelled as being for rim brakes.

My understanding is that you cannot attach a rim brake to a disk-compatible rim, since the sidewalls are not designed to withstand the stresses. However, it is not obvious to me whether there would be any problem attaching a disk brake to a wheel with a non-disk rim (assuming that it's been built around a disk-compatible hub, and is attached to a disk-compatible frame).

Is there some problem with this configuration? The obvious drawback would be carrying around the extra weight of a reinforced rim, but that doesn't seem to prevent the wheel from actually functioning.

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What an awesome question! Low-end MTB frames and forks come with both rim and disc brake mounting posts, so why not flexible wheels too. –  Vorac Nov 6 '13 at 14:32
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Yeah, should be no problem. Of course, the rim and hub need to agree re number of spoke holes, and you need to have the right length spokes. And the wheel needs to be laced in a cross pattern to properly transfer torque between rim and hub. –  Daniel R Hicks Nov 6 '13 at 16:16
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3 Answers 3

up vote 6 down vote accepted

There's no problem mounting a disc-compatible hub to rim-brake compatible rim. Just make sure they've got the same number of spokes and you're good to go.

You're absolutely right about the opposite though, disc brake rims generally do not have a braking surface on them, the rim profile is round there, so it wouldn't work. And if you did try to brake on it, it a) wouldn't work well and b) would probably cause excessive rim wear.

What you could do, if you want to be flexible and switch back and forth is to get a dual-duty rim that supports both, such as the WTB Dual Duty FR rims (probably a bit beefy, but you get the idea).

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Sooo, are those meant to have 4 brakes on a single bike? Muhahha! –  Vorac Nov 6 '13 at 14:36
    
I suppose you could! Can't say I've seen it, but it would certainly be possible. Imagine how crowded your handlebar would be too! –  Aaron Nov 6 '13 at 14:59
    
@Vorac: Maybe :) jail.sine.com/sheldonbrown/sheldonbrown.com/harris/… –  whatsisname Nov 6 '13 at 16:40
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Or this? niagaracycle.com/categories/… –  Carson Reinke Nov 7 '13 at 18:44
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The one thing to be aware of is that disk brakes put more force on the spokes during breaking than rim brakes. Mostly this is not an issue as long as you do not use radial spoking.

If you build up the wheel with 3x and anything but super silly light spokes, it should be no problem at all.

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Disc brake hubs are dished almost equally left/right. You will want to make sure your road/touring rim is not an asymmetric rim, designed for dishing on one side and not the other. This Ritchey Girder is an example:enter image description here

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