Deployments of city-wide multi-hop 802.11 networks introduce challenges for maintaining client performance at vehicular speeds. We experimentally demonstrate that current network interfaces employ policies that result in long outage durations, even when clients are always in range of at least one access point. Consequently, we design and evaluate a family of client-driven handoff techniques that target vehicular mobility in multi-tier multi-hop wireless mesh networks. Our key technique is for clients to invoke an association change based on (i) joint use of channel quality measurements and AP quality scores that reflect long-term differences in AP performance and (ii) controlled measurement and hand-off time scales to balance the need for the instantaneously best association against performance penalties incurred from spurious handoffs due to channel fluctuations and marginally improved associations. We utilize a 4,000 user urban deployment to evaluate the performance of a broad class of hand-off policies.