The dropper post length is dependent on a couple of factors; the first being your saddle height and the second being the maximum seatpost insertion depth which you’ll find listed below. Using the values below and the charts supplied by the dropper post-manufacturer you will be able to figure out which dropper post length is best for you.

Altitude Powerplay carbon:

Size S = 166mm

Size M = 205mm

Size L = 230mm

Size XL = 268mm

Altitude Powerplay alloy:

Size S = 193mm

Size M = 231mm

Size L = 270mm

Size XL = 308mm