sentences:  Also note that, in any of the double- or triple-differential steering methods, the efficient turn radii (e.g., with no steering clutch or brake slipping) are determined by the ratio between the steering input speed and the main drive input speed into each epicyclic final drive.This means that having multiple ratios in the steering transmission results in multiple turn radii for each main drive transmission ratio.The additional complexity in the mechanical systems and driving controls means that this capability is rarely implemented.