In comfort bicycles from Alter Cycles used a frame with swap different down tubes. It’s actually more curved, flexible bow-like … thing, that’s available in three levels of stiffness and the stiffness of the ride can be altered to suit the rider.
Mark Groendal, an inventor of the Reflex, essentially redesigned the classic diamond frame that was designed over a hundred years ago. By modifying the front triangle into “the modified triangle” that flexes changes everything about the ride and the performance. All of the Alter Cycle comfort bikes have an interchangeable flexible downtube made of a much stronger, more resilient steel than traditional chrome one. This tube allows and limits the frame flex.
In Alter Cycle calls it “linear flex” which, while ridden, is an almost continual stretching and retracting of the frame and wheelbase in small amounts. This motion smooths the ride and helps keeps the tires on the ground much better. The interchangeable tubes Rider Fit Tubes, or RFT’s, are designed for different weight riders. There is a #1 for riders up to 90 kg, #2 up to 115 kg and #3 up to 130 kg. The surprising thing is that everyone who tested these comfort bikes preferred the most flexible tube for their weight range. Not only is the ride smoother, the bike frame actually performs better as it flexes. The smoother ride still retains responsive steering and maintains a nice road feel.
Moreover, Alter Cycle is an amazing comfort bike. It handles semi-rough roads pretty well and excels at street cycling and is a must-have for all cyclists at any level.
In detail https://altercycles.com