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The Truvativ Hammerschmidt is a crankset that has an internal-geared-hub mechanism built into it.

From a BMX standpoint, this is a much better solution, because almost all internal-gear rear hubs greatly weaken the rear axle. You don't want to do huge drops on a IGH.

By moving the IGH mechanism to the middle of the bike, you allow your axles to be as strong as they need to be.

Info about the Hammerschmidt itself: [1] [2] [3]

The Hammerschmidt is part of SRAM's business, so it's a reliable brand.