Delay optimization is an important issue for ad hoc wireless networks supporting multimedia applications. Current medium access schemes do not take the application packet size into account for their operation. Long packets win the channel contention equally likely as the smaller packets; however, they occupy the channel for a longer time. This unfairness leads to increased delay and jitter for smaller packets. This paper attempts to resolve the above issue by proposing a fully distributed algorithm that adapts the contention process to the packet size as well. More specifically, we emulate the shortest job first scheduling policy by proposing a new resetting backoff regime. The proposed scheme is then compared to the distributed coordination function of the IEEE 802.11 standard. Analytical and simulation results show that the delay of the small packets is significantly improved.