A typical bottom bracket on a bicycle frame is around 10.5 inches off the ground. Multiplying that by 2 you get a maximum extension of 21 inches. This is the theoretical limit of crank extension without lifting the bicycle off the ground. This is fine for stationary elliptical where you can lift the bike but for mobile elliptical this is a concern especially as clearance is needed for the road and road debris and turning. 18/19 inches is feasible but we want more. While still under wraps we have a design (may be physically impossible but hey that is research) that is a new mechanism take on a classic mechanism/assembly. More news on that if and when it works.