The MacPherson strut is an excellent solution for front wheel drive suspensions that has been used worldwide by car manufacturers. Besides the advantages of this suspension it presents many difficulties due to the characteristic of being a bending structure. Little attention has been given to the contribution of the MacPherson strut flexibility to vehicle dynamics. The flexibility of the structure affects the suspension geometry, mainly the camber angle, and this influences the vehicle handling and the driving safety. It is presented the effect of forces and bending moments on the piston rod, reservoir and pressure tubes and their contributions to the suspension flexibility. It is discussed the effect of the several standard piston rod diameters commonly used and the influence of the variation of the bending resistance arm. The effects of other parts are also analyzed, as the tensile strength, design safety factors and other important data. All results are based in design data of several actual vehicles in production using a proprietary computer software developed for suspension design and optimization.