This is the popular fast rolling surly knard 29er plus folding mountain bike tyre whats 29 its a tyre meant for rims with a bead seat diameter of 622mm 29 but large volume and ideally shaped when used on a very wide rims in this case knard is a 3 tyre designed for 50mm rims the larger diameter smooths rolling over rough ground the increased volume adds a bit of suspension and float the width increases traction and the sheer size holds speed well the profile is round and tracks