Zipp 404 Pave as a disc rim - how many spokes is enough?

[Exar]

I have a Zipp 404 Pave wheelset (actually labeled as American Classic Carbon 58) which is 20/24 holes front/rear. I'd like to use them in a disc wheelset for my cyclocross bike. I know that 20 holes is not a lot, but there are 20 hole front hubs available... So I'm tempted to give it a try. I weigh around 77 kg on a good day and I've only taco'ed one front wheel in 15 years of racing and training.

The wheel would only be used in races in The Netherlands, meaning either sand or mud, no long downhills (not really any downhills at all). The wheels held up fine as rim brake wheels so I'm not too fussed about the durability of the rims themselves.

Any thoughts?

[FIJIGabe]

I wouldn't do it. The stresses put on the wheel by the disc brake action need additional bracing. The few grams you are losing by removing 4 spokes are hardly a good trade-off if you're risking (or worried about) a wheel failure.

Furthermore, 404's are large wheels (and the Pave's, being reinforced, means that they're probably heavier than the standard 404), far larger than you will ever need for CX racing. Really, all you're doing is running a large rim with compromised brakes. That certainly sounds like a recipe for disaster.

[romalor]

24 spokes minimum

[grover]

I once rebuilt Easton EC90slx tubulars into disc wheels. That's an 18 spoke front wheel with a rim that's probably half the weight and spokes a fair bit longer. It worked. I did 100km trail rides on it with steep decents, roots, rocks. It was not stiff but you adapt to what you're riding. Would I have raced on it? No. But not because I was frightened it was going to blow apart through general riding. Rather because the lateral stiffness was poor and other wheels allowed me to ride faster.

The wheels got decommissioned when i cased the rear wheel into the landing of a gap jump and cracked the rim. The rim failed, the 24 hole rear rim built 2 cross both sides. The wheel build did not fail. I deconstructed the front wheel to use the hub on another build.

I went down this route because the wheels when built as rim brakes where reversed over by a car and the braking surface was badly damaged rendering them useless for rim brakes. Had the wheels been worth anything as a rim brake build I would have just sold them and bought something designed to be a disc brake wheel.

I think your 20 hole front rim will hold up under braking forces. I also think that lateral stiffness will be better than my experiment because the rim itself is stiffer. Would I do it? No, I'd sell the wheels and buy some disc brake wheels. The rim brake hubs you'd be left with are worthless.

[Exar]

The rear rim has already been repaired following a failed bunnyhop incident (the price you pay for trying to look cool during a race). The braking is fine for cyclocross however the slight bump that the rim now has makes subtle braking (like in a crit) a bit iffy.

The 404 Pave rim is around 360-380 grams, isn't it? I was hoping the reinforcements (the 'Pave' bit) would make it hold up better. I'll ponder it some more, perhaps new wheels are a better idea.

[grover]

In that case the rear rim is worthless. Build it as a disc wheel definitely. The rear rim will work fine as a disc wheel being 24H
The front, give it a go. If it's a flexy noodle pull it apart and sell the rim (or rebuild as rim brake wheel with original hub and sell).