It all depends on how often and how hard to you ride the tandem as well as the quality of the components and, most importantly, the quality of the build. If the 36h 3x wheel is using a true tandem hub, has robust spokes, is laced tightly with uniform tension then you could probably enjoy several years of trouble-free use if you only ride the triplet a couple hundred miles a year on nice roads and don't climb a lot of big hills or do a lot of aggressive riding. If, however, you and the boys will be logging big miles on epic rides, I'd rethink your strategy based on the following.
Originally Posted by pablopsd
What you're trading-off is an almost indetectable amount of weight reduction (noting most of the 48h wheel weight is likely in the Phil Wood hubs, i.e., not rotating mass), is somewhat diminished bike stability and control, reduced service life and reduced safety margin:
- Stability: The 48h wheels, if built well, will have less side-to-side deflection under cornering or any other time that side-loads are put on the wheels compared to the 36h wheels.
- Control: The more robust your wheels are, the better the bike tracks and turns.
- Service Life: Short of bashing a pot hole and wearing through sidewall brake tracks due to extensive riding in wet conditions, fatigue life is what limits a wheel's total service life. A 36h wheel's spokes, rim and hub will carry a higher load per spoke than a 48h wheel and that combined with more deflection will make the lower spoke count wheel more susceptible to fatigue wear.
- Safety Margin: Broken spokes are usually a fact of life on a triplet and other, larger multi-seat tandems given the very heavy loads they carry. Riding a triplet home on a 48 spoke wheel with a broken spoke is a non-event as the wheel barely goes out of true and the increased load on the remaining 47 spokes is minimal. On a 36 spoke wheel, busting a spoke with a 400lb load means your rear wheel will go way out of true and the damage to the other spokes will likely require a rear wheel build as you can usually count on having additional broken spokes in the future if you simply replace the one broken spoke.
Bottom Line: It's all about how you use the equipment and how well matched components are to your use. For folks who rarely ride their tandems almost anything will work.
For folks who log thousands of miles on their tandems each year under demanding conditions and where reliability is essential (think 50 miles from home on an epic ride, bombing a mountain descent at 60 mph, riding with disabled stokers or dropping $10k on a cycling tour) then cutting corners for no reason other than vanity is pretty short sighted. If, on the other hand, you're competing in a competitive event and have full SAG support with a spare set of wheels and/or even a spare bike near at hand, you can get away with all kinds of bizzare stuff to shave off weight since durability and reliability can be confined to short periods of time or a specific event, after which marginal specific-use equipment can be rebuilt or replaced.