It's the Chainstays. You need two bars connecting the bottom bracket to the rear...

		ogre_codes on Feb 10, 2020 \| parent \| context \| favorite \| on: Ask HN: What’s the most important modern simple in... It's the Chainstays. You need two bars connecting the bottom bracket to the rear hub or the rear wheel is extremely unstable. Most modern bikes are fundamentally 2 triangles joined at the base.