skikes 150mm wheels are light and give off very little friction due to the low surface area. You can gain speed and distance on paved paths or travel through long stretches cross country - all with one type of wheel. In the beginning, 150mm wheels are better suited for training routes with paved paths and only some grass/gravel.  Advanced skikers can take these wheels anywhere.200mm wheels have lots of air-volume and relatively low air-pressure. The suspension reduces strain on the joints. The dimensions of the 200mm wheel, in combination with the suspension, makes an easy and comfortable journey on dirt/grass/gravel/forest-paths and more. 200mm wheels are suited for training on almost any path (grass, gravel,forest,paved,etc) but require a little more energy when going longer distances.