In this paper, a group based preamble selection is proposed for dynamic assignment of bandwidth to User Equipments (UEs). Conventional non-group based preamble selection suffers from low detection probability under multipath fading channel namely extended vehicular A (EVA). The contention BR in Long Term Evolution (LTE) networks shows improved performance when group based preamble selection is combined with uniform backoff mechanism. Simulation results conclude that uniform backoff with grouping shows an improvement of 14.35% and 32.92% than conventional uniform backoff and binary exponential backoff without grouping, respectively.