Originally Posted by
cyccommute
Explain how that would work. What is the heavier rim doing that the lighter rim won’t?
I am merely relating my experience. I may be an exceptionally heavy tourist. We did carry a pétanque set with us at one point. And a couple of lawn ornaments we had found. Small BBQ also. Tried to make ourselves at home in our campsites over the year or so we spent on the road. I will explain below why I think it happened this way.
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.
My hypothesis for my experience is that heavier rims are less flexible so they spread the load out. You mention the spoke tension decreasing above the contact patch. Yes. I think this effect is more spread out on a heavier, less-flexible rim. Thus, more spokes share in it so the overall effect on each individual spoke is lower. Also, often I find I can build with a higher tension if I use a heavy rim. This may help to insure nothing ever comes completely loose under any extreme circumstances (e.g. hitting a poorly graded cattle grid with a touring bike carrying a pétanque set and a bottle of Grand Marnier and a Campingaz grill in addition to the usual sundries). We pulled spokes through the MA3 rims, completely destroying them. We saw cracks developing in the A319 rims a couple times. But we never broke a Rigida Sputnik. We also broke many spokes with the MA3, but not with the A319 or the Sputnik. Not sure what else could be responsible except the extra metal in the rim.
While the Santana wheels look interesting, I think you are misrepresenting what they do. First, the rims aren’t heavier.
Santana says
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.
Seems to be working for them in spite of it all. I would like to know the weight of their 16-spoke rims, as well, but I can't find a weight figure to compare them to the usual ~500g Mavic fare available in 40-hole. I held one in my hands at a trade show a while back. It felt like a touring rim, certainly. That has been my experience with a lot of these modern low-spoke-count deep-section rims. They are heavy.
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.
I agree with you, I like triple butted spokes for all these reasons. 13/15/14ga, the equivalent of 2.3/1.8/2.0, sure. But I don't like them enough to rebuild an existing wheel with them. They are nice but they are pricey! Any new wheels I build are usually with the Sapim Force unless it's a budget build.