We propose adaptive data rate multicarrier direct-sequence spread spectrum (MC-DS-SS) systems for transmission over a frequency-nonselective Rayleigh fading channel. We investigate two different novel transformations to be used at the transmitter that switch between conventional Serial-to-Parallel (S:P) and split transformations based on the knowledge of channel state information, a pre-selected threshold and a majority-vote decision. The selection of threshold is crucial and it directly affects the performance of our adaptive systems. We provide results to show that our adaptive system is flexible as it allows the user-selection of operating points. Our results also show that our adaptive transformations are advantageous than S:P in terms of bit error ratio performance and advantageous than split in terms of data rate.