Efficient multihop traffic management is a need for successful Wireless Mesh Networks (WMNs) deployment. Using an analogy with fluid mechanism, we classify a flow as laminar if the packets flow smoothly from the Wired Access Point (WAP) over the mesh network, and as turbulent otherwise. We identify a particular but frequent collision scenario, which sets the flow to be turbulent, resulting in a strongly reduced downlink end-to-end throughput. We show that the exponential backoff mechanism in an 802.11WMN is responsible for this problem and suggest a modification of the current exponential backoff policy of 802.11 for WMNs. We support these findings both with simulations and real measurements on a testbed infrastructure.