After three years of pre-production testing and three additional years of deliveries, here are Santana's easy-to-digest tech notes for Shimano's tandem-specific Sweet-16 wheels:
1). Per Shimano's original instructions (supplied with every set of wheels), new Sweet-16 wheels require an initial retensioning after 1000km---or earlier if the wheel makes noise. While many owners or their mechanics have guessed that the nipples somehow loosened, the initial drop in tension is instead the normal-and-expected result of the seating of the spokes and rims. Prior to the upgrade to lighter rims (wheels built after August 2005), many customers skipped this important service. With the improved wheels this required initial service will be harder to ignore.
2). Even when they have a tensiometer, veteran wheelbuilders may disbelieve the very high tension requirements of these wheels. If the spokes are only tightened to a traditional "racing wheel" tension (which is about half of what Shimano recommends), the wheel will make additional noise as the nipples begin to loosen. If spokes are tightened to 80% of the recommended tension, the wheels may feel and sound fine, but the spokes will fatigue prematurely. Repeated service or premature spoke breakage has caused some wheelbuilders and/or their customers wrongly believe that these wheels are "high- maintenance," "fussy" or "weak." Actually, as long as these wheels properly retensioned per Shimano's original instructions (after 1000km or as soon as they make noise), Sweet-16 tandem wheels will generally remain tight. Laboratory fatigue tests that simulate years of demanding use demonstrate that a properly tensioned Sweet-16 rear wheel will outlast traditional 160mm tandem wheels with 40 spokes (and 145mm wheels with 48 spokes). A triplet team weighing 520 is successfully using Sweet-16 wheels. A number of strong tandem teams (some over 350 pounds) have now logged over 15,000 miles without incident. The key to years of reliable service is the initial re- tensioning.
3). What is the proper tension? When using a Park tensiometer the recommended average tension for all spokes is "26." With Wheelsmith's tool we recommend a reading of "95." Loc-tite is unnecessary.
4). Unfortunately, most customers don't have access to an accurate spoke tensiometer. If there is any question as to adequate tension of a Sweet-16 REAR wheel (the wheel that seats further and faster), anyone with a good ear can make a quick assessment by plucking a few spokes. Because the 32 identical spokes of these dishless wheels should all have the same tension, front and rear spokes should produce comparable tones. And while not every spoke of true and properly-tensioned wheels will vibrate at exactly the same pitch, if you want to verify proper overall tension a piano is generally faster and more accurate than a tensiometer. Plucked spokes that sound a note lower than an F-sharp signify low tension. (Among a trio of black piano keys, the F-sharp is the one on the left). If the wheel is also untrue, it should be tensioned by an expert wheelbuilder. If, on the other hand, the wheel is perfectly true, a conscientious amateur can carefully tighten all sixteen spokes by one-quarter turn. After rechecking for trueness, if the wheel's tension is still low this process may be repeated.
FREEHUBS:
5). For years Shimano has employed a lightweight proprietary pawl grease that acts as a barrier to prevent the heavier bearing grease from gumming up the mechanism. Exceptionally trouble-free, "pawl skip" will occur when this barrier grease is displaced through EITHER over-packing the axle bearings OR oiling the mechanism. Although the resulting skipping can be cured through cleaning and proper re- lubrication, it is generally cheaper and easier to replace the thread- on mechanism. Formerly a tandem-specific item, for the past four years Shimano has used this same easy-to-replace part on their XT and XTR mountain bike hubs.
SPOKE SPACERS:
6). A combination of rainy-day grit, hard use and/or low tension can "saw through" the plastic "frisbees" that separate the spokes. Because the wheels work equally well with or without them, this need not be a cause for concern.
NOISY FRONT HUBS:
7). Very rarely, an improperly-assembled front hub creates mystifying
sounds as a result of a missing or misplaced ball-bearing. The cure
is to make sure each race has an equal number of balls, and that none
are trapped between the races.