Originally Posted by
elcruxio
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.
There is only a slight difference due to rim shape and the rims that are marketed as being “stronger” are typically wider, flatter models like the
Velocity NoBS (620g in 700C) or
Atlas (620g) or
Cliff Hanger (675g). They are heavier and wider so the
must be stronger, right? Even the high profile rims like the
Deep V (580g) only offer marginal compressional strength over something like a
A23 (450g). The Deep V is far narrower as well so it doesn’t offer much lateral stiffness as
Dyad (535g) or A23 do. Both of those are significantly wider. The Deep V does offer a shorter spoke length which is something of a plus.
Full disclosure: I do have Deep Vs on my touring bike. I don’t have them because of the strength and some would question using a rim with a 14mm internal width with 32 to 38mm tires. I don’t have a problem with the tires but others might. I don’t find them any different from any other rim I currently use, however. I still build with triple butted spokes because that’s where the strength is needed…not in the rim.
All things considered, however, I’d have no issue touring on an A23. It’s stiff enough and strong enough for touring. It’s also the only rim in the Velocity line that offers off-center drilling which goes a very long way in terms of wheel strength by significantly reducing the drive side/nondrive side tension imbalance.
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.
Are broken rims a common problem? I’ve built, used, and destroyed a lot of wheels as well as rebuilt a lot of those destroyed wheels. I’ve worn out only a handful of rim brake rims in 40+ years of riding and building. I’ve cracked quite a few more rims. But I’ve, by far, broken far more spokes. A worn out or cracked rim can be relatively easily replaced as long as the rim is the same or has the same ERD without changing out the spokes. The wheel is just as strong as it was before.
However, the common wisdom for spokes is that once you’ve broken a few of them…estimate range from 2 to 5…the wheel needs to be rebuilt with brand new spokes. The reason for that is that the other spokes tend to get stressed with a spoke breaks and can ultimately fail as other spokes break. In other words, a broke rim is a fairly minor repair. A broke spoke is far more serious and more likely to result in needing a new wheel.
My wheels with Dyad or A23 rims or even the slightly heavier Deep V are equally strong but weigh significantly less.
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.
Aluminum rims need the double wall construction to make them stiff enough for use in a wheel. Single wall aluminum rims are around and they aren’t all that strong nor stiff. My point with steel rims is that even with a single wall, they are very stiff and strong but they aren’t any less prone to breaking spokes than aluminum is.
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.
Again, you are giving credit where it isn’t due. High profile rims have been available for a very long time. Bad spokes aren’t less likely to break just because of the rim’s profile. The improvement in materials
of the spoke has more to do with the wheel strength and ability to use few spokes. As a large rider carrying heavy loads and riding in tough conditions, I still wouldn’t trust a low spoke wheel to stand up to the rigors that I put my wheels through. But I also realize that I don’t need to drag around hundreds of more grams of wheel weight than I need to
if I use a better spoke.