Friday, May 12, 2006

Wheel Thoughts Continued

Rim Eyelets – Many rims have eyelets which are visible as a “lip” around the edge of each spoke hole. Rims will come with no eyelets, single eyelets, or double eyelets. Rims with no eyelets have a simple hole through the wall of the rim for the spoke and spoke nipple to pass. Often, the edge of this hole is rough and must be filed smooth by the wheelbuilder. Such spoke holes can damage nipples, and, for this reason, I do not use aluminum nipples with such rims. Brass nipples are fine, but they still require rough edges to be filed smooth to prevent damage.

Rims with “single eyelets” have a separate, smooth ring placed into each spoke hole. This helps to prevent damage to spoke nipples and allows the nipples to turn easily.

Rims with “double eyelets” have a unique socket in which the nipple rests. This socket connects the exterior and interior walls of a double-wall rim to allow both to share the load from each spoke.

Rim Profiles – Rims come in a fairly wide variety of profiles, but most fit into single wall, box section, or aero categories. Most inexpensive rims are single wall rims. These can be steel or aluminum, and the cross-section of such a rim looks like the letter “U.” Single wall rims are generally not available with eyelets. Box section and aero rims with double walls cost a little more but increase the strength of the wheel greatly. For this reason, it is rare to see single wall rims on a handbuilt wheel.

Box section rims have both an interior and an exterior wall. A cross-section of such a rim looks much like a single wall rim with the addition of the second wall connecting the upright portions of the “U.” Box section rims are available with no eyelets, single eyelets, and double eyelets. A variation of the box section rim is the “triple box” section rim which adds to additional walls connecting the interior and exterior walls. The cross-section of these rims looks like a regular box section rim with the “box” divided into three smaller boxes. This design permits the interior and exterior walls to share the load in the same manner as the double eyelet.

Aero rims are generally tall and have a triangular cross section. They are not only more aerodynamic than box section or single wall rims, but they are generally quite strong as well. You will often see aero rims built with fewer spokes than box section rims. Aero rims are available with no eyelets or single eyelets, but double eyelets are uncommon.

Rim Anodizing – Most rims on the market today are anodized. Anodizing prevents aluminum rims from corroding. Alternate corrosion prevention treatments are polishing and powder coating. One side effect of anodizing is that it can make the surface of the aluminum more brittle. This effect is greater on rims that are “hard” anodized. These rims can usually be identified by their dark gray color. Some anodized rims will exhibit cracking of the rim around the spoke holes. The solution for some builders has been to use less spoke tension on rims with known issues. However, this technique results in a less durable wheel. For that reason, I do not recommend hard anodized rims and prefer polished or powder coated rims.

More to come . . .

1 comment:

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