Semi-active suspension control needs to measure the relative velocity of the wheels respect to the vehicle body to regulate the damping forces. Linear potentiometers are the most used sensors in racing for linearity and simplicity, but they are expensive for mass market and unreliable in the long run. The paper deals with two different approaches to design a soft sensor for the on-line estimation of the suspension velocity from acceleration signals. Main features of the soft sensor implementation according to each methodology as well as the corresponding experimental results are discussed with reference to an extensive measurement campaign carried out with a motorcycle test bed.