The IEEE 802.16 standard is designed to meet the need of metropolitan-area broadband wireless access. This work studies two collision-resolution requesting schemes for best-effort (BE) traffics in IEEE 802.16 networks. One is the exponential backoff scheme defined in the standard and the other is a piggyback mechanism enhanced by single-frame backoff, called the Request Piggyback (RPB) scheme. We analyze and compare their performance in terms of the request success probability and the packet delivery delay under Poisson traffic. The results show that the RPB scheme outperforms the exponential backoff scheme and can reduce request collision.