Spinning is a completely self-directed exercise. Irrespective of who the instructor is on a given day, I tailor the workout to my training schedule. If I am doing base building, then I spin with greater RPMs and lower tension. If I want to get my heartrate up, I add tension. As is stated above, it is much easier to deal with spinning classes if your instructor is actually a roadie (or otherwise a cyclist) and is specifically doing the workout to make you better on your bicycle. But, even if the instructor has no real cycling experience, you can still do what you want. Make lemonade out of lemons.