Ratio of belt tension:

For Open belt drive:

Angle of contact (θ) for larger pulley = ∏ + 2α Angle of contact (θ) for smaller pulley = ∏ - 2α For cross belt drive:

Angle of contact (θ) for larger pulley = ∏ + 2α

Angle of contact (θ) for smaller pulley = ∏ + 2α

(that is for both the pulley, it is same)

But for solving problems, we take the Angle of contact (θ) for smaller pulley

Hence,

Angle of contact (θ) = ∏ - 2α - for open belt

Angle of contact (θ) = ∏ + 2α - for cross belt