Your camera has no Motocross Mode? Lousy one! :bsmilie:
Jokes aside .. maybe Sports Mode could help? There is no magic setting, you need to analyse a) what do you want to capture and b) the existing conditions. Both give the input for the necessary settings. In addition, your equipment gives you some limits like maximum aperture and image quality at such settings (some lenses are soft when used wide open, stepping down a bit helps). Learn to understand the "triangle of exposure": ISO, shutter speed, aperture. That will give you the answer(s), together with the intention.
Do you want to freeze motion? Then shutter speed would have priority ... hence ... I hope you guess which mode to take. Do you want to have slight motion blur? Or panning shots? Then vary the settings accordingly. Still objects isolated from background? Aperture is most important here (beside the distances camera - object - background) - so it would tell you which mode to take.
Not happy with either one? Then Manual gives you full control but requires you to think about everything.