Originally Posted by
cyccommute
The problem is that the “stronger, stiffer” rim doesn’t have anything that makes it stronger nor stiffer. If you look at the profiles of the rims, the rims that are supposedly “stronger” don’t have any thicker material. They are usually wider or taller but they use the same wall thickness as narrower rims. No extra metal is added except that needed for the extra width or height. I’ve done calculations based on the profile and the increased volume of of wider or taller rims and all of the extra metal is accounted for by the change in dimension. A “stronger” rim to me would mean one that has more metal to provide that strength.
Shape is more important than wall thickness. A taller rim is going to be stronger and resist deformation than a shallower rim that has the extra material put to wall thickness. That isn't to say that wall thickness doesn't matter because it obviously does. However it is less important a consideration than shape.
Typically your average strong touring rim is going to have a pretty high profile. Of course then there's deep V's which probably wouldn't be a bad choice overall.
Of course then there are reinforced spoke beds like the ryde andra line of rims, but that doesn't directly affect the stiffness of the rim. Then again there's also added wall thickness in the andra rims overall so they're pretty beefy and indestructible. My tourer has andra 321 with 36 DT Swiss alpine 3's. Those are pretty strong wheels.
Additionally, if you change the metal of the rim from aluminum to steel, the steel rim is significantly stronger and stiffer than an equivalent aluminum rim. It would resist the decrease in tension far better than an aluminum rim will but even the significant increase in strength doesn’t provide any protection against spoke breakage. Spokes still break on steel wheels.
Now that all would be true if all factors were equal. But they aren't are they? There aren't any steel rims with the same profile and wall thicknesses of aluminum rims. Steel rims typically have pretty squat profiles and they lack the double wall construction of aluminum rims as well as the material uniformity and wall thickness variability you get with extrusion. If you've got a solid block of material or a piece that's a bunch of folded sheets, the solid block is going to be stiffer.
Hjertberg has another, far nerdier,
article on spokes in which he posits that the increases in wheel strength are due to better metallurgy of the spokes.
There's probably a lot of truth to that. that's one of the reasons why I'm looking into rope wheels. Dyneema wheels can get crazy light and the rope material is much better at handling detensionings than steel. And since it's multiple strands there's no material uniformity to worry about.
The ability of low spoke count wheels to better withstand the rigors of riding has less to do with the rim than the far better spokes we have available today. I have no problem doing off-road bikepacking trips on some of the lightest, (presumably) weakest rims around…395g Mavic XC717 or 422g Velocity Aeroheats. But I pair them to DT Apline III or Pillar triple butted spokes. I went from regular spoke breakage pre-Alpine III use to no spoke breakage post Alpine III use. I haven’t changed how I build.
One of the reasons why wheels can go with lower spoke counts is higher rim profiles. Once high profile carbon rims entered the foray, you could effectively build "smaller" wheels with shorter spokes and with the added benefit of a rim that exhibits practically zero deformation in any direction.