Cycling west from Oppdal, Google Maps will suggest this side road:
That's Fv513. The main road is Rv70.
Choose Fv513 if you don't like traffic. Rv70 has a lot of 80 km/h traffic when the walk/cycle path ends after around 8 km. The remaining 12 km to Lønset you're riding in traffic. Fv513 is a bit hillier, but the views are mostly obstructed by trees. It's roughly half tarmac half dirt/gravel. You see a nice waterfall near Lønset.
Be prepared to follow the road to the right at this intersection, which shows up in the middle of a big descent:
