When adjusting a trike to fit a person, the X-Seam measurement is the critical factor to know. This measurement determines how far away from the bend in the seat the crankset is placed. If you are being fitted for a trike, you will be asked to sit in the recumbent seat, wearing the same shoes that you will be wearing when you ride. You will then extend one leg straight ahead, placing the heel of that foot against the pedal, which will be extended out forward. The knee must not be bent while doing this adjustment. The person adjusting the trike will then slide the boom as necessary so that the pedal touches the heel of your shoe, and will then tighten the boom into its permanent position just for your measurement. Finally, the chain will be adjusted as necessary to fit the length.
For folks who are ordering trikes at a distance, where a personal fitting is not possible, give the trike shop your X-Seam measurement so they can adjust all this for you, without you sitting in the seat. This method is not as precise as the personal method mentioned above, but it will be pretty darn close, if not right-on. One can then micro adjust the boom once the trike is received if they are skilled in this procedure. This micro adjustment will not necessitate any chain adjustment if the dealer was using your X-Seam measurement and did a good job.
Below is how Hostel Shoppe describes taking one’s X-Seam measurement, which should be taken by another person as you just sit there. Taking one’s own X-Seam measurement often results in faulty measurements. From the Hostel Shoppe Guide Page comes this information:
Place a 24 inch long board against a wall with the bottom of the board 12 inches from the wall. Sit on the floor with your back and butt against the board. Your X-seam measurement is the distance from the front of the board to the heels of your bare feet.