<div class="htmlview paragraph">In this paper, a friction estimation method using a tire vibration model is proposed. It is based on the frequency characteristics of the wheel speed vibration which are related to the tire-road friction. The recursive least squares and the instrumental variable method are applied for online estimation. The experimental result shows that the proposed method applied to free rolling tire detects friction change from dry asphalt to iced road at constant speed without braking, accelerating or cornering.</div>