"60% reduction in space is misleading - it may be a 60% reduction in diameter but in terms of  volume, the reduction is much smaller - about 7% if for calculation you assume the unfolded wheel is 40mm thick and the folded wheel is 332.5mm thick (i.e. the radius of the unfolded wheel now projecting into the screen, as it were) and approximate the shapes to solid cylinders. Nonetheless the folded shape may be more convenient/efficient for shipping and storage depending on the shape of the space you have to put it in and what you are shipping it with."