I thought I'd experiment with using a different track type to create more interesting racetracks that could be paved with scenery and the track made invisible. This is kinda fascinating. Karts teleport past wide (45degree) turns but have no problem with other turns, including the sloped ones. The loop was just to see what happened and the answer is they lose momentum going into the "uphill" and slowly rise to the top before gaining momentum on the "downhill."