My schedule is tight, so most mornings, I'll only have time for about 30 minutes of riding. I typically do between 6 and 12 miles (give or take), some gentle hills, some gentle downhill, some sprints, a little cruising. It gets the heart going, the legs working, but doesn't kill me. At the weekend, I can typically venture further afield and undertake 20 miles or so.

Is this decent exercise for moderate weight loss and getting in shape for perhaps trying some short road races?