OK, I am jealous of many here who talk about their 'typical 35 mile ride' - On MY schedule, it's all I can do to squeeze in 15 miles a day during the week - I actually change in my office at work, gear up, top off tires and hit the road for 45-50 min. to get that 15 miles in. (Weekends are a bit different, but I'm concerned about the weekday ride) My question is - do you have any suggestions to maximize the effectiveness of that short 15 miler? I'm looking to build strength, endurance and overall fitness. Should I just work on reducing overall time for the 15 miles? Should I force myself in to higher gears? Higher cadence? Sprints? Any suggestions??