Slip characteristic of a tire is essential for controlling braking, traction, or stability of a vehicle. In this paper, we propose a new method to measure longitudinal slip characteristic using a developed plate brake tester. The slip is calculated based on the plate displacement instead of the angular speed of the wheel. An algorithm for modelling the relationship between friction force and slip was made using Julien’s Theory. The algorithm was verified through a simulation. With this method, the longitudinal slip characteristic of a tire can be obtained quickly. The brake tester developed in this research is potential to be used as indoor test equipment for simulating a tire in various road conditions.