Mountain Bike Wheel Size Compared Take a look at the video below as Donnie Harries compare the different mountain bike wheel sizes. Which do you prefer? the 27.5 or the 29. Listen as he compares the advantages of the 27.5 and 29 inch and takes a test ride on each. Santos Bike Shop – Comparing Mountain Bike Wheel Sizes from Erin Freel on Vimeo.