Friction measurements on real road surfaces are limited because of the necessity of complex measuring systems which are not available in the field. This investigation is important to improve vehicle dynamics and tire design. To perform this task a mobile measuring platform to measure the friction coefficient between a rubber testing wheel and the road surface was built. The main requirements of the system are autonomy (integrated energy source) and mobility. The measuring device is integrated into a 3-wheel robotic platform that is driven by two rear wheels and a non-driven but steered front wheel. The experimental results shall classify different street surfaces and give the influence of surface pressure and sliding velocity on the friction coefficient.