I'm not an impulse buyer, but a 24 hole Powertap for under 200 bucks was a bargain I couldn't resist. Hub acquired, the next question was what rim to use. The 24 hole drilling limited options and applications.
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| The Beast. It is laced 2x on both sides using Sapim Race spokes (2.0/1.8mm) |
Possibilities (ranked $$$ to $)
- 50mm Carbon clincher (520 grams)
- 50mm Carbon tubular (400 grams)
- HED C2 tubular or clincher (439/478 grams)
- Velocity Chukker (664 grams)
- Velocity A23 (450 grams)
- H Plus Son Archetype (~460 grams)
Note: these rims are all 23mm or wider.
I settled on the A23 which was available in 24 hole and is a good combination of weight/cost. The only downside is the rim's 601mm ERD; it is a shallow rim, so it is not as tolerant of high spoke tensions. It is this characteristic that is significant with Powertaps.
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| Velocity A23. Made in the USA! |
There are two knocks on Powertap hubs:
- they're bricks. The one I am using is about 430 grams. Compare that to a White Industries T11 at 260 grams. It would be a significant weight penalty to carry in a race, unless paired to a stupid light rim, or mounted on a very light bike.
- their geometry is compromised. The Powertaps have a large hub shell because it is stuffed with electronics. The transmitter electronics are stuck on the outside of the NDS flange. The effect is that the NDS flange moves towards the center of the hub, significantly affecting wheel stiffness on the NDS side. (Google Powertap spoke detensioning and you'll get lots of hits.)
For #2 compare the Powertap's center to flange measurements with the run-of-the-mill Dura Ace 7850 (in parenthesis): DS center to flange 17.4 (21.1); NDS center to flange 31.7 (36.9).* The closer the flanges move to the center of the wheel, the less laterally stiff a wheel becomes. This becomes especially relevant when using a box section or low profile rim which will be less stiff laterally and radially.
Given the special hub and rim properties, extra care had to be taken when building this wheel. I deburred the spoke holes on the rim. (If the drilling wasn't clean, the leftover material can cause spoke wind-up.) I used 14mm brass nipples (more tolerant of spoke tension, less friction against the aluminum rim, and more supportive of the spoke). Lastly, I made damn sure there was little variance in spoke tension. The tensiometer got a lot of use. This was a slow build process.
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| Continental GP4000s. The finest clincher out there. I will fight anyone who suggests otherwise. |
The wheel is a gem. I rode it for several weeks before turning it over to Mateo. It was plenty stiff radially and laterally. There was zero brake rub, even when mounted to my v-brake equipped cross bike. The spoke tension, with a tire mounted and inflated to 100 psi, is: 100 Kgf on the driveside and 47 Kgf on the non driveside. That might seem low, but the tire is a 700 x 25 Conti GP4000s mounted to a soft, low spoke count rim. I am probably losing 10 percent or more spoke tension due to the compressive force of the tire/tube on the rim.
* The venerable DT Swiss 240 is has a DS spacing of 17 and 33.2.
