[Note: this is #1 in a series of tips to be published during 2009.]
Hexagon headed fasteners have dominated engineering for a century but bicycle wheels know better and every spoke nipple (well, 99.6%) in the world is square drive. Why? Even though square drive cannot transmit as much torque (twisting force), lower tolerances are required than with hex drive. Besides, if you plan to turn a fastener with just a two sided wrench (an open end wrench), then square drive is equivalent to hex for strength.
Since wheel building involves lots of separate adjustments and turning, it’s no surprise that open ended wrenches do the bulk of work. They’re easy on and off. Hence, square shaped nipples are dominant for bicycle wheels. My advice (Tip No. 1) is to use a three-sided spoke wrench whenever possible. See the difference:
Visualize each of these wrenches turning a square spoke nipple. Imagine the points of contact, the nipple being somewhat smaller than the wrench.
- The two-side wrench has two contacts. The back inside surface of the wrench cannot drive because any force against it will push the nipple away. Only the sides hit the nipple, so we have two contacts.
- The Park style (SW-40) of three-sided wrench slides onto the spoke first, then over the nipple. See how the two lips adjacent to the entry slot make it impossible for the nipple to move away from the square opening. Notice that the wrench will drive the nipple with three contacts.
- The diamond shape (DT, Spokey, Minoura, Hozan, and more make these) three-side wrench also slides over the spoke before the nipple can enter. See that the wrench makes contact in three spots and the somewhat enclosed nipple has more trouble deforming and rounding off.
The last two styles can effectively deliver twice the torque, making nipple destruction nearly obsolete. A two-side wrench is good for a seat bag toolkit, but don’t depend on it for regular use.
In addition to using three-side wrenches, always lubricate the nipple-to-rim contact. Add light oil when truing an older wheel and before a new build becomes snug. Thread friction is much lower than the nipple-to-rim friction.
If you work on many types of wheels, you must have encountered splined shape nipples and wrenches. Mavic is best known for this. These spline shapes also make it easy to turn tight nipples without damage. But what about custom builds, when you’re not using proprietary Mavic parts? Consider using Spline Drive nipples. Spline Drive is a conventional shaped nipple that was developed in LA in the early ’90′s, unfortunately a decade before its time. Unable to support a one product industry presence, they gave up. But the design is still valid.
Can you see how 6 effective driving edges for this nipple makes for a much stronger wrench-to-nipple interface?
As splined nipples (by a variety of makers) find their way back into the market, please welcome them. I know a number of custom builders who will switch as soon as the supply is stable. FSA, for one, is beginning to use this spline nipple shape on their standard wheels. The deciding factor for this trend is the increasing popularity of aluminum nipples. They save only a tiny amount of weight over brass nipples but they’re easily colored and more in the spirit of contemporary performance cycling.
Aluminum nipples suffer because, while lighter, they’re weaker than brass. They are more easily deformed in turning. Aluminum also has a higher friction coefficient, which means they turn more stiffly against a spoke or rim than brass. Thirdly, aluminum is more vulnerable to corrosion. A corroded nipple is harder to turn as the oxides act like glue, bonding the nipple to its spoke. For multiple reasons, aluminum presents trouble for torque. A three-side wrench or splined shape allow twice the torque to be transmitted. Not a trivial improvement.
So, use three-side spoke wrenches and welcome spline drive type solutions into the wheel world. Spend your valuable time optimizing component combinations and introducing uniform and appropriate spoke tensions. Spend less time struggling with stiff turning and deformed nipples.