This paper develops a quite simple yet very accurate mathematical model for performance analysis of 802.11 ad hoc networks with traffic flow diversity (i.e., packet size and arrival rate diversity). The results show that 802.11 ad hoc networks can achieve very low packet delay and maximum throughput in non-saturated conditions. Furthermore, when the normalized total load is less than the critical value, the throughput of each station is approximate to its load and the packet delay is much lower than that in saturated cases despite the packet size and arrival rate diversity. The simulation results show the analytical model is highly accurate.