Dropper post length is dependent on a few 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.

Instinct Carbon 27.5" wheels:

Size XS = 185mm

Size S = 210mm

Instinct Carbon 29" wheels:

Size S = 210mm

Size M = 235mm

Size L = 250mm

Size XL = 280mm

Instinct Alloy 27.5" wheels:

Size XS = 225mm

Size S = 225mm

Instinct Alloy 29" wheels:

Size S = 225mm

Size M = 250mm

Size L = 275mm

Size XL = 275mm