December 21, 2011 7 Comments
[Note: this is #14 of a series of 20]
You have undoubtedly noticed, and I mentioned in tip #4, that spokes do not exactly conform to their path once laced into a wheel. This is especially true at the hub. With higher quality hubs and spokes, the spoke elbow seems incomplete, resulting in a bowed shape before full tension is applied.
This bowing is, indeed, owed to incomplete elbows. Better spokes, those destined for high end builds, have short elbows and a more open angle like 105° rather than 90°. Better hubs also have smaller spoke hole diameter and thicker flanges. Consequently, the spoke can be laced through the hub but it doesn't fall down to the correct angle towards the rim. Why?
It turns out that bending a spoke after it has been laced maximizes contact with the hub and significantly increases fatigue life. Spokes that drop easily into holes and swing to correct angle without resistance end up with less support. At the same time, spokes on the inside of the non-drive rear hub flange do not need much elbow length or angle. You see, spoke positions in a pair of wheels vary as to exit angle.
For these non-drive side spokes, the incomplete elbow is a perfect fit. Were the elbow larger, it might become opened a bit as tension is applied, which reduces fatigue resistance. Since we're happy about these miss fits, because they extend spoke life, what technique is appropriate to make sure the fit is perfect?
Some builders favor hitting the spoke with a hammer, close to the elbow. I see three problems. One, there's no striking elbows on the flange inside surface and there's a chance some of those spokes could use straightening. Second, few hub makers design flanges to resist hammer blows. Spare those hubs! Third, hitting a wheel 16 or more times with a hammer is invitation for a miss. Leave hammers to carpenters.
The way to quickly and consistently bend incomplete elbows into perfect hub contact is a lever.
Insert a round rod, like a big Phillips screwdriver blade, or handy piece of scrap steel, into the large triangle defined by the cross pattern. Angle your rod so it bends an outside and an inside elbow at the same time. It will be obvious which way to apply pressure.
Go around the wheel giving a forceful push to each elbow. If you push too hard, no worry. The spoke is not seriously harmed. Ease up. No need to struggle and unbend the over-corrected spoke. Do this setting procedure when the wheel is laced but still has low tension. Notice how loose the wheel becomes. The old school practice of letting tension do the elbow setting is inadequate because spoke metal needs an over correction, like any steel, so tension may appear to straighten the spoke but it still has a memory of its original shape. As you ride and tensions vary, your spoke will be returning to its shape, constant flexing, eventually leading to breakage.
I'm glad to know you won't be ignoring elbow shape and spoke path. These geometries are fundamental to wheel function and you need to be making optimal adjustments so your wheels are as perfect as they can be.
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