Determination of Angle of Contact

When the two pulleys of different diameters are connected by means of an open belt as shown in Fig. (a), then the angle of contact or lap (q) at the smaller pulley must be taken into consideration.

A little consideration will show that when the two pulleys are connected by means of a crossed belt as shown in Fig. (b), then the angle of contact or lap (q) on both the pulleys is same