I leave it on the lowest setting on the flats, and I am going 15-18 instead of 12-13. With 60+ pounds of bike and gear, the lowest boost setting gives a good workout. I have one hill that is a mile at 12 degrees and another that is 1/2 mile at about 15-16 degrees. I put the bike on the second of the four boost settings. To keep it working well I need to hold 90+ on my cadence. So, my knees are saved by the torque of the motor, but my lungs still get a workout on those hills. It is not as intense, but it is still a workout and my knees can do this every day, whereas they cannot do three consecutive days on my other commuter.