This paper is about the estimation of the tire vertical deflection in a motorcycle suspension. The tire vertical deflection is assumed to be directly related with the contact forces between the tire and the road. Therefore this measure can be extremely useful to implement control strategies oriented to the maximization of the road-holding of the vehicle. Unfortunately, the actual measure of tire vertical deflection is possible just by contactless distance sensor such as optical sensors, which are not suitable for practical industrial applications. The aim of this work is to propose alternative layouts of sensors to estimate the tire vertical deflection, by means of observers based on the Kalman-filtering techniques. The experimental results show that, among the proposed sets of sensors, the best trade-off between cost and estimation performance seems to be the use of vertical accelerometers placed at body and wheel side.