First, please don't obsess over the sizing decision. The Swift frame is remarkable in that it accommodates a large range of uses for cyclists of almost any size and shape. Part of the reason for this is that the seat post has a great deal of vertical adjustment and is oriented at 72 degrees, which means that adjustments to the seat-to-pedal distance simultaneously change the horizontal reach of the bike as well. The basic frame on the Swift fits riders from 5'0" to 6'7" tall. This range is accommodated by changing up to three components, the length of the seat post, the extension of the handlebar stem, and the riser. If the size isn't perfect, it is easily adjusted without having to return the bike to the factory.
We define our sizes as follows:
Size S - You are less than 5'5" (1.65m) tall.
We remove 3 inches (75mm) from the seat post and install a short stem.
Size M - You are between 5'5" (1.65m) and 5'10quot; (1.78m) tall.
No changes are made to the Swift. The stock seat post and stem are used.
Size L - You are between 5'10" (1.78m) and 6'2" (1.88m) tall.
We keep the stock seat post and install a long stem.
Size XL - You are between 6'2" (1.88m) and 6'5" (1.96m) tall.
We install a longer seat post (590mm) and a long stem.
Size XXL - You are between 6'5" (1.96m) and 6'7" (2.01m) tall.
We install a longer seat post (640mm), a long stem, and a taller riser (300mmL).
If you want to fuss with the micro-level details of frame geometry, feel free to check out the frame geometry specifications.