Bought a used zipp 404 firecrest 20 spoke powertap wheel, and while there is at least 2-3mm clearance between the tire and the underside of the ultegra direct mount brakes, I can easily deflect the wheel enough to generate some great squeaks from the tire contacting the brakes. It is not the pads that it hits, it’s the brake itself.
The spokes are thin bladed spokes, and after reading this: Debunking Wheel Stiffness - Slowtwitch.com
“What this adds up to is the perfect wheel storm: An astoundingly stiff, deep-section carbon rim – strapped on to a handful of thin aero spokes. The stiff rim can literally overpower the spokes. If your rim rubs your rear brake pads, this is probably why.”
I am thinking of just rebuilding the wheel with meatier spokes.
Has anyone tried Sapim CX-Sprints? Anything else out there to consider? I don’t want to downsize the tire, I want to try to get a less noodly wheel.
Unfortunately your best bet is more spokes, but that’s not gonna help unless you buy a whole new wheel. CX-Rays are the gold standard of spokes, CX-Sprints are - according to Sapim - similar to these but stiffer. That’d be my choice.
I’d find out spoke tension (harder to guess with bladed spokes) and likely increase it before trying anything else. I’ve seen similar wheels with virtually no tension in the spokes, especially on the LHS of a rear wheel - which is loose in a best case scenario - but sometimes crazy low if the drive side aren’t at/near maximum tension.
Is the wheel deflecting or the hub/frame connection? Maybe try a steel QR (a trainer QR for example). Are the spokes tensioned well? (Try a phone app to see if they are somewhat close if you don’t have a tension gauge), Are you using the thinner pads for thicker rims or normal pads?
Using what you have, Powertap 20h and Zipp 404. How are they laced? Maybe you can lace them with all the spoke heads toward the interior, giving you a slightly larger bracing angle.
I’d get some thick spokes. I don’t think rounder will help, but just more material. You’ll need to ream out the spoke holes a bit with a dremel and a diamond ream. I’d try Pillar 1432 aero spokes, which you can find for a reasonable price from CSC on ebay relative to Sapim/DT Swiss.
If the nipples are external, you can try making them internal. I don’t think anyone makes an internal nipple for a normal sized hole though, maybe try a washer. This should net a bit more bracing angle.
How flexy are your bars? are they wide? you might might be able to reduce those instances by limiting arm leverage maybe with narrower bars or flexier drops - along with the steel trainer QR to stiffen the axle.
I’ve rebuilt heaps of wheels with stronger spokes due to my higher than average weight, and slightly higher than average power.
When choosing a spoke look at the weight, bladed vs round makes no difference to the stiffness. The weight indicates the amount of material and therefore the stiffness.
CX rays are good spokes, but very thin and flexible as you have noticed. They are roughly equivalent to a flattened (bladed) Dt Swiss revolution, which is 1.5mm round in the centre and 2mm at each end. They weigh about 4.4g each.
The step up from that is something like a Dt Competition race, 1.6mm in the centre, weighs about 4.9g per spoke. The the standard Dt Comp spoke, 1.8mm in the centre, 5.9g per spoke. Then a straight gauge 2.0mm spoke like the Dt champion weighs about 6.8g per spoke.
Since you’ve only got 20 spokes, I’d go for something like a straight gauge champion spoke. They are the stiffest and since you’ve only got 20 spokes it’s not much of a weight penalty. Bonus is they are the cheapest.
If you want a bladed equivalent look at the Pillar 1423 spokes. They are slightly bladed and will fit through a normal hub spoke hole. As a bonus the Xtra version is 2.2mm at the elbow, to give it a bit more strength at the most common failure point. I’ve had good success with these, I’ve built several wheels with them and haven’t broken one yet.