Okay, first let me say I am a VERY CASUAL rider. I know basically very little about bikes - just when the tires are flat and they need air. I recently took my barely used Jamis Citizen (2005) out with my sister riding. She rented a bike and I rode my Jamis. As I mentioned, the bike has barely been used and I looked it over well before I went out. I noticed that I was having to push a lot harder than she was to go the same distance - using any of the gears. At first I thought it was because I was out of shape, but then we switched bikes and I was able to cover much more distance on the rented bike than on my own and she also noticed the difference.
Any thoughts as to why this is happening and how I can fix it? I'm taking it to a shop tomorrow.
Thanks for the help in advance.