What is a 29er?

A mountain bike with 29-inch wheels, commonly called a "29er," is a relatively new development in the world of off-road riding. Standard mountain bikes have 26-inch wheels, and since the development of 29ers, are sometimes referred to as "26ers." Off-road cyclists who ride 29ers praise them for offering numerous advantages over 26ers, 

Cube Bikes and Giant have entered the burgeoning 29er market for the first time in 2012.  They've used their Agile Ride Geometry to combine all the advantages of 29in wheels with those of the smaller 26in. They say they’ve achieved this by having a bottom bracket height identical to that of the smaller frames, plus a specially mounted front derailleur to give adequate tyre clearance, which means shorter seatstays for quicker handling.