The mathematical description of chain-wheel drives with two fixed non-cricular wheels, a transmission chain of constant length and g give non-costant velocity-ratio leads to a system of nonlinear functional equations. It seems impossible to solve this equations, but we can construct a set of tangents of thesse wheels by kinematic methods. The desired curve can be approximated by constructing spline curve. This paper considers piecewise raional cubic Bezier curve which has all these tangents as tangents, the curve is G²-continuous and shape-preserving.