Recent benchmarks indicate that the use of public key cryptography results in non negligible verification times on platforms with limited processing power. In this paper, we focus on multi-hop Inter-Vehicle Communication and show that the increase in message processing time in vehicular nodes degrades network performance, decreasing the number of messages that reach destinations. We propose Adaptive Message Authentication (AMA), a lightweight filtering scheme that reduces the number of cryptographic operations performed by the nodes. Although based on local observations and without any additional communication channel between the nodes, our scheme achieves global improvement of network performance. We perform extensive simulations and show that our scheme resists DoS attacks and brings significant improvement even against a substantial number of adversaries in the network.