Rate adaptation is a highly challenging task in MANETs, mainly when relative fairness among competitive nodes is considered. Existing rate adaptation solutions are mainly designed for IEEE802.11-based WLANs. They do not cope with relative fairness. Unlike these existing schemes, the main objectives of our proposed approach, called REFOT (Relative fairness and Optimized Throughput), are to ensure fairness and to allow each node to adapt its transmission rate and contention window to its channel quality. The channel quality is determined by calculating for each node the probability to access the channel in a distributed manner by approximating the number of successful and failed transmissions. REFOT allows for reaching the appropriate transmission rate level, without crossing all the intermediate levels. This operation helps in avoiding scenarios where the network capacity could be underutilized or overused, allowing the system to reach its stability faster. We validate the proposed model via analytical model, based on a 3-dimension Markov chain, and simulation results. Via extensive simulations, the performance of REFOT is evaluated and compared against that of some existing schemes. In the performance evaluation, different node densities, mobility models, transmission ranges and network TCP/UDP traffic loads are simulated. The obtained simulation results are encouraging and indicate that REFOT achieves its design goals: it ensures a good trade-off between fairness and throughput.