by Ric Hjertberg of Wheelsmith, from Toe Clips Fall `92
This is surely a mechanical year to remember, with an avalanche of new groups, 8-speed setups, cassette hubs from all over, a proliferation of carbon wheels, suspension systems and exotic materials left and right. But think of it this way: the more exotic it gets the more crucial the role of a well-informed mechanic, and amatuer teams and fields pose the maximum challenge with their unpredictable equipment diversity. Let’s consider a few wheel-related topics and my observations and advice.
The use of aluminum nipples is growing fast. They save weight and vary a lot. Some of the better designs utilize 7000 series forged aluminum, weather resisting anodized coatings and greater thread length. But regardless of nipple quality, pay more attention to lubrication which fights the higher friction that these nipples suffer from and it will limit the corrosion that can cause them to fail. Most light oils work well if applied during building and/or added later to the nipple/rim contact areas. The most important consideration is noticing what nipples you are working with. Don’t dive into a fast spoke replacement without observing the nipple type so you can use a bit of extra caution in case they aren’t brass.
In the same vein, beware of titanium these days. Its a fun material and makes a great replacement for steel here and there. But its softer, exhibits higher thread friction and it’s often a bit less-strong than steel. Look at each fastener, whether it’s a crank bolt, derailleur or cantilever pivot, stem bolt, seat lug bolt, etc. Use extra caution with titanium and usually extra lubrication. Eventually you will develop a “sixth sense” for these pieces but you’ll never stop noticing which material you’re working with. Nothing is quite so depressing as a fastener failure in the field that could have been avoided. You won’t always be able to blame the material.
Spoke tension is one of those wheel variables that a field mechanic must understand. Remember that measured tension will go down about 20% when a high pressure tire is inflated. This is normal and OK, just don’t mistake an inflated wheel for one that has “loosened up.” Wheelsmith’s preference for 80-100 kgf refers to a bare, pressure-less wheel.
So don’t try to make up for too-few spokes in a time trial wheel by overtightening them. You can make small increases in wheel strength but possibly encourage rim cracks at each nipple or an uncorrectable rim kink if a spoke breaks. By the same token a 48 spoke wheel usually cannot be tensioned to the same average tension as one with fewer spokes. Many good rims cannot support 48 spokes at 100kgf. Load them up and they’ll become unstable, going out of true often. Beware youwill regularly encouter wheels that are unstable because they are too tight. They have usually reached this state becuase someone either 1. forgot that tension goes down with tire inflation or 2. tried to “fix” a wheel that has loosened nipples by overtightening. Your cure is quick and painless: simply loosen the victim, cement or crimp the left side nipples (if a rear) and expect a stable result.
To compare the sideways strength of various wheels, just look at the center-to-center flange distance for the particular hub as listed in Sutherland’s Manual or the Wheelsmith Spoke Length System manual. The larger the number, the better the triangle supporting your rim. Some of the latest 8-speed setups are no worse than the 6-speed wheels of years past.
Keep track of your observations and questions as if you were a journalist collecting notes for an article. Get your questions answered. Sometimes they are unanswerable but the very quest will often reveal some valuable information.