I should also mention that the main purpose of a trainer should be to do stuff you can't do on the road. For instance pedal for a solid hour at a high moderate pace without stopping. On the road one has to stop all the time for lights, signs, etc. and there are hills which allow you to coast instead of keeping a steady effort. Or work on high cadence pedaling, say 40 minutes at a steady 115-120 cadence in a very low gear. Again, can't do it on the road. Or do one-legged pedaling. Ineffective on the road because of all the inertia. Very effective on the trainer. Etc., etc. Call it "out of the envelope" cycling.