Shadow Torrid V2 Cranks

Flipping through Dan's I saw the shadow Torrid cranks. Now I realize these are not new, but they are interesting. If you take a look at the patent for it, they originally designed the crank to use a chromoly spine (4140 not specified), with an aluminum shell. I'm not sure if they ever made this in a production run, but there are a few reasons why this is not necessarily a good idea:

• Different materials have different properties. Specifically, they have different elasticity, and different rates of thermal expansion.
• Joining (welding) dissimilar materials is difficult. Although there are filler materials available for joining Aluminum and Steel, but they make structural sacrafices in order to get proper fusion of both materials.
• There is no purpose in using two materials. Profile and the new Torrids show how steel is enough on its own.

Now the current version of the Torrid cranks use a 4140 spine and a 4130 shell... Again, I am not so sure this is really necessary, or even advantageous. We can't really know what their goal in using different materials is. However, we can speculate they wanted the stiffness of 4140. I assume they weld the shell to the spine along the ridge, which would stiffen the whole structure by making virtually the whole crank a heat affected zone. Well they could post weld heat treat (anneal), as all welded components should be, but I would assume they would market that as well.

After running a few circles, where are we? Boasting that it is patented, the use of two parts, and two materials, all makes me weary this is mostly just marketing. Does that mean they are crap and will break? No, not at all. But if we are to aim for the highest strength to weight ratio, this design is probably not the way to go.