Friday, February 20, 2009

FAQ - Part 5

Previous FAQ installments available here, here, here & here.

Why use bladed spokes on cross wheels or climbing wheels? Why use hidden nipples on a cross specific wheel?

Sure, aerodynamics may not be the most important consideration when choosing a climbing wheel or cross wheel but it still matters. And you if can make a wheel more aerodynamic without increasing weight or compromising strength, doesn't it make sense to do so?

First off, let's talk about the pointlessness of building a wheel just for climbing. With the exception of uphill TTs, very few wheels are ever going to be ridden exclusively uphill.
Generally, you're going to have to ride to the hill in order to climb it and then down the hill you've climbed. So, aerodynamics and solid braking are always going to be considerations.

Our 22L generally weighs in at 1280 to 1300 grams. There are surely lighter wheels out there but not too many offer the cost and braking advantages of an aluminum rim. None of them will be anywhere near our price of $480 and most use round spokes based on the flawed assumption that aerodynamics doesn't matter on a lightweight wheelset.

Now with cyclocross, aerodynamics arguably matter less but you're still out there moving at a decent rate of speed and you're also less likely to be in a pack compared to a road race so better airflow doesn't hurt. In my experience, bladed spokes also clear mud more easily. We also recognize that even though we build the 50x and 25x for cyclocross, a lot of our customers are looking for a more solidly built road wheel and some people will use them on both their road and cross bikes (although that's a lot of gluing and ungluing for my taste).

Now, as for the hidden nipples on the carbon wheels go: yes they are more aerodynamic. The farther out on the diameter of the wheel you go, the more aerodynamics are going to be a factor. That said, they are 10x more expensive than traditional nipples and more difficult to work with when building the wheel. Maintenance will also be an issue since you will need to remove the tire to true the wheel or replace a spoke if needed. So, if aerodynamics were the only benefit, hidden nipples would not be worth the cost.

There is, however, a much more important consideration: strength. I've seen a lot of carbon rims either fail at the spoke hole or "pucker" at the spoke hole after hitting a pothole, curb, log, etc. With traditional nipples, you need to drill a relatively large hole in the rim bed. With spokes at high tension, the stress on the rim is concentrated around the edges of this hole. By drilling a smaller hole and using a larger hidden nipple, this stress is spread out over a larger surface area, minimizing the chance of damage upon impact. Using hidden nipples on an alloy rim would provide the same benefit but to lesser degree - the chance of a rim failure is less and cost to replace the rim is lower.

As for the issue of maintenance, we use a conservative build for our carbon wheels 20/24 spokes for the 50 and 24/28 spokes for the 50x. We also build carefully to tight tolerances. It depends a lot on your riding style, weight and other factors, but the wheels should not need to be trued too often, if ever, unless you've really knocked something out of whack.

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