Sour’s Purple Pie: When Steel Meets Software
Sour’s new Purple Pie combines handmade German steel with a Pinion electronic gearbox. It’s a rugged, low-maintenance expedition rig for the curious builder.
Gravel bikes seem to be on a steady, inevitable march toward becoming 1990s mountain bikes, and I am entirely here for it. The latest evidence of this evolution is the "Purple Pie" from the German manufacturer Sour. It’s a steel expedition frame that seems to ask, "What if we took away the most fragile part of the bike—the derailleur—and replaced it with a transmission?"
The Purple Pie is built around the Pinion Smart.Shift gearbox. For the uninitiated, this moves the gearing into a sealed box at the bottom bracket, electronically shifted and totally impervious to mud, grit, or the baggage handlers at the airport. It’s a fascinating mix of old-world durability (handmade Saxon steel) and modern integration (3D-printed battery doors and electronic shifting).
What strikes me most isn't just the "apocalypse-ready" nature of the drivetrain, but that Sour is selling this strictly as a canvas for a project. It’s sold only as a frame kit—you get the steel skeleton, the gearbox, and the shifters, but the rest is up to you. It fits massive 55mm tires (basically mountain bike rubber), meaning this is less of a race machine and more of a heavy-duty overland rig. It’s not cheap, and you have to wait for their small-batch production cycle in February, but there is something undeniably appealing about a bike built to survive just about anything you can throw at it.
