Sorry if this is in the wrong section or is a dumb question , I am new.
I have recently purchased a Diamondback Insight 1 Hybrid Bike (2011 version) for general commuting to and from work/school. On average, I will probably ride about 4 miles (7k) a day, with the odd day averaging up to 10-20 miles. My max has been 25 miles.
I have trouble keeping a good speed. I average maybe 15.5 MPH, going up to 17-18 mph for short periods of time, however I feel the burn! My legs fatigue fairly quickly I must say. I ride at level 2 with the gear at 5 for flat roads (mostly), 6-7 when I feel like going fast and 4 for going up hills. My seat is placed up high and I am riding on pavement.
Its pretty frustrating because I am not a fat guy at all... I'm about 195 pounds, 6 foot 1 and I play soccer. I can easily run 8-10k. I want to cycle consistently at around 17-19 mph for longer periods of time. Getting a new bike is not an option... I started going to the gym with a focus on building my leg muscle.