Instrumented and subjective cab ride quality data is obtained for a COE tractor/trailer combination in which two different cab isolation systems were installed. In the first system, the rear of the cab is suspended on soft springs while the front is pinned to the frame, allowing cab pitch only. In the second system, the rear of the cab is pinned to the frame while the front is suspended on soft springs. The relative performance of these two systems is compared. Results are compared with predictions of a multi degree of freedom tractor/trailer computer model.