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Sunday, July 12, 2009

Bicycle Wheels: Loctite or Not

One topic not covered by our lectures on the bicycle wheel is the loctite issue. Many wheelbuilders swear by loc-tite or spoke-prep when building wheels, and it's a question that comes up on a regular basis on cycling forums.

I don't build using loc-tite. If you pay attention to the lectures, you'll see that at one point, I say, There's no such thing as too much lubrication. I emphasize this especially when building with modern rims such as the Velocity Aerohead, which have no eyelets or sockets whatsoever, but also when it comes to the spoke-thread/nipple interface.

To consider why loctite is unnecessary if your wheel is built to the correct tension, consider why a spoke can unscrew itself. The spoke is effective a very long screw under tension. As long as there's tension in the screw, the screw can't unscrew itself! It can only do so when there's no tension. The loss of tension comes from there being a big load on the wheel, which is absorbed by the spokes loosing tension. If the spokes aren't sufficiently tensioned, then the spokes will unscrew themselves, which will lead to the wheel becoming untrue. When the wheel becomes untrue, then, that's your warning that your spokes were insufficiently tensioned, and you should re-tension your wheel.

What happens when you loc-tite the spokes instead, is that the spokes don't unscrew, but they do flex a bit, usually at the elbow (spokes flex even if they are lubricated and unscrew, so it's not a good idea to under-tension wheels, regardless). Eventually, if the elbow flexes enough times, the spokes break and then your wheel really becomes untrue.

So you have a choice: have your wheels go untrue so you notice the problem, or have the spokes break eventually. Now you know why so many professional wheel builders loctite their wheels --- a wheel becoming untrue happens really quickly, but spoke breakage can take many cycles (and a lot of people just don't ride their bikes enough to do that). In general, then, I consider use of loctite/spoke-prep bad practice, and usually used to cover up sloppy wheel building. There might be reasons to justify it, but if you're building wheels for your own use, just use lots of lubricant and none of those "miracle" preparations.

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