Disc Wheel w/ rim brake to Disc Brakes?

Question

I have a zipp disc wheel that is for rim brakes. Is it possible to convert it to a disc brake?

I’m thinking it might be possible by replacing the hub/mount for the disc brakes but I’m not sure on that. Also, I don’t know if there would be enough clearance for the disc brake components on that wheel? Any advice/help would be greatly appreciated!

Thanks!!

Answer 1

Similar questions about converting bikes that lack disc mounts have been asked, but I'm not sure if there's a duplicate question on converting wheels.

For a general wheel, the conversion process would mean that you need to remove the hub and spokes, and mate the rim to a disc hub. The original hub will lack any disc mounting tabs. It also wouldn't have been designed to withstand the torque transmitted by the braking action, so welding the appropriate disc mounts would not seem optimal, even if you had the skill and the ability to redo the aluminum shell's heat treatment. This doesn't seem economical, although it might be theoretically possible for someone with the engineering resources if they were absolutely dead set on doing this regardless of the economics.

In any case, this would also open up an ontological question: you would have reconstructed a key component of the wheel if you did the previous, and much more likely you would just have bought a new disc hub, so is it a conversion or basically a new wheel with an old rim? Also, I'm not sure how well a rim brake rim will withstand the forces incurred during disc braking, particularly the ones transmitted through the spokes. The rim bed might not be strong enough. I do not know this bit. In any case, if you had sentimental attachments to that rear wheel for some reason, this is a more subjective consideration that you might want to think about. I suppose you could post the question to the philosophy Stack Exchange site.

You specifically asked about a disc wheel of the sort used in time trials and triathlons. I am not that familiar with their methods of construction, but I am assuming that the disc bit is structural, and that the hub shell is bonded to carbon. So, in addition to the engineering difficulties I described earlier, it seems like you are now adding some challenges in reworking carbon. You would have to find a new hub shell. It would have to have the same dimensions as the previous one, and by that I mean all the physical aspects of the shell unless you want to enlarge the hole where it bonded to the carbon - and there could be implications for the wheel's structural integrity if you did this because you are cutting through fibers, and you do want to be careful if you do that. By the last part of the sentence, I basically mean that nobody without practical composites repair experience should even consider it, just in case there is a problem that leads to a structural failure.

Answer 2

The conversion of a wheel from rim brakes to disc brakes happens by swapping the hub and the spokes. Disc front hubs are asymmetric so they might require bit different spoke lengths. In some cases, it might be possible to reuse some or all of the spokes.

However, you do have to be aware of certain possible issues:

• Radially laced front wheels cannot be used with disc brakes, but however when respoking you can choose a different spoke pattern (although then you'll have to throw away all your existing spokes and start with fresh spokes because spoke pattern affects spoke length)
• Disc brakes require enough spokes, or else you'll encounter a catastrophical loss of spoke tension, particularly on the front wheel where braking loads are high. With rim brakes, the wheel could have less than 36 spokes. With disc brakes, you don't want that unless the hub has a particularly large flange. The reason is that spokes see alternately their tension being reduced and increased. With too few spokes, the spokes there are need more tension change to transfer the braking loads. One of those spokes that sees a tension loss is at the bottom, where it sees another tension loss from the weight of the cyclist. When braking hard, 100% of cyclist weight is on the front wheel. Then 100% of the cyclist weight is on the single bottommost spoke, and also the bottommost spoke has to transfer its share of braking loads. The combined effect of these two tension reductions could reduce the tension to zero, thus causing the nipple to vibrate loose.

I don't know the details of your wheels, but I'm 99% certain the magic word "Zipp" refers to a brand of boutique wheels that almost certainly has too few spokes.

Do note that changing a wheel hub requires about 4-5 hours for an amateur mechanic. A professional wheelbuilder could perhaps halve that time. It doesn't generally make sense to invest so much time to a wheel that won't be durable. Thus, when building disc brake wheels, you'll want an adequate number of spokes, so much that the wheel lasts not 100 km, not 1000 km, not 10 000 km, but 100 000 km at least. Such durable wheels need enough many spokes.