The width of every BiSaddle is adjustable. There are four bolts on the underside which can be loosened so the padding can be adjusted more wide or more narrow. After your custom fit width is found the bolts are tightened to keep the padding locked down at the desired width. This is similar to adjusting your seat post height. Once the bolts are tightened the saddle or seat post will stay locked in place.
Rails: CM and TI rails are round and will fit all seat posts. Carbon rails are oval and will only fit top clamp or oval specific seat post clamps. TI reduces weight by 20 grams compared to CM. Carbon reduces weight by an additional 20 grams compared to TI.
Relief Zone: A channel reduces some pressure in the middle of the saddle and provides more surface area for your sit bones to ride on. A cut out further reduces soft tissue pressure, but due to the reduction in saddle surface area the sit bone pressure may be a little higher.