Originally Posted by
scarlson
I don't agree. All things equal, a wheel with a heavier rim, with more metal in it, will be less likely to break spokes than one with a thinner rim. Dish also matters a lot. Dishless tandem wheels can be very strong in spite of a low spoke count.
First, I used to tour on a 36 spoke rear wheel made with a Mavic MA3 rim (470g weight), and broke three rims and ten spokes before lacing the same spokes and hub to a Rigida Sputnik (745g weight), and it has not had any trouble under the same conditions. Same builder (me), same spokes, same hub.
Explain how that would work. What is the heavier rim doing that the lighter rim won’t?
Rim strength has very little to do with wheel strength. You can take the strongest, stiffest rim around…a steel one…and build with weak spokes. The wheel won’t be “strong” because the spoke are weak. Alternatively, you can take the strongest spokes…2.3/1.8/2.0mm triple butted spokes…and lace them to a “weak” rim and still have a very strong wheel. The spokes are what breaks, not the rim. The rim isn’t really attached to the spokes. It is free to move on the spoke during riding and does so as each point on the rim approaches, is directly over, and passes by the contact patch. The rim deflects upward, decreasing tension on the spoke Go into a corner and the spokes are still the part that takes the brunt of the lateral forces on the wheel.
I always build with the lightest rims I can find and seldom have wheel breakage issues…even on loaded touring bikes.
Second, Look at Santana's tandem-specific Shimano wheels, which only have 16 spokes, but are dishless and have special, heavier rims. According to Santana, they were subjected to the same mechanical test trials as Santana's 40-spoke wheels and the 40-spoke wheels broke first.
While the Santana wheels look interesting, I think you are misrepresenting what they do. First, the rims aren’t heavier.
Santana says
…Surprisingly, these uniquely proportioned rims weigh no more than the weaker rims found on other tandems.
Second, the spokes put different stresses on the rim than conventional spokes do. I would question the longevity of the rim sidewalls with the spoke pulling on a weaker part of the rim than conventional spokes do. They say they are reinforced but that is still a bad place to put the spokes.
I would also love to have more spokes, yes. But above 36 you get into specialist tandem components. Heck, even getting 36 is hard sometimes. I put an ad up looking for a 135-spaced silver 36h rear cassette hub and have had no responses in two weeks. And even tandems are going to heavier rims with fewer spokes now.
The key isn’t necessarily
more spokes but better ones. The triple butted spokes, suggested above, are about the equivalent of added 4 to 8 (perhaps) spokes to the hub. They are significantly stronger than straight gauge spokes and don’t require proprietary rims to build them. Most every hub is drilled to pass a 2.3mm spoke through the hole in the hub because that’s the increase that rolling on the threads puts on the spokes. The heavier bend increase fatigue strength about 50% which makes for a more durable wheel.