The aim of this study is to define optimal construction of brake piston (material, seal position) in caliper. Stress level and distribution, deformation and weight were examined to find optimal thickness where seal position (seal in caliper, seal in piston) was changed. Three materials were examined in finite element software (2D axisymmetric model): aluminium alloy (3.4335), steel (1.0039) and titanium alloy (3.7165). Pistons parameter tested: diameter 44 mm, height 29 mm, If the material is aluminium alloy the wall thickness is 2.69 mm, in case of steel the thickness is 4.02 mm when the seal is in the groove of piston. When the piston material is titanium alloy, the wall thickness is 0.8 mm having the seal in the caliper. The weight is critical issue in brake systems, so, the optimal wall thickness defines then piston weight. Weight of aluminium alloy is 0.045 kg, weight of steel is 0.153 kg and weight of titanium alloy is 0.047 kg. These weights show that aluminium alloy piston offer the lightest construction in case of maximum pressure 15 MPa.