From the construction, the rivets joining the pieces forming the belt do not come into contact with the surfaces of the pulley, and from the tension of the belt causing it to wedge into the sides of the pulley groove, the driving power is greater than that simply due to the area of contact and the tension of the belt.
Fig. 2703.
A belt will run to the largest diameter of a pulley, thus in [Fig. 2703], the belt would, unless guided, gradually creep up to the side a of pulley p, and following this action would move to side c of pulley d.
Fig. 2704.
If the pulleys are parallel, but the axis of their shafts are not in line, then the belt will run towards that side on which the axes are closest; thus in [Fig. 2704] the belt would run towards the side p of the large pulley, because the belt b will meet the pulley surface at a, and if a point on the belt at b travelled coincident with the point on the pulley with which it took contact, its plane of rotation, while on the pulley, would be as denoted by the dotted line b.
But to follow this plane of rotation, the belt would require to bend edgeways, as denoted by the dotted line b, which it does to some extent, carrying the belt with it.