If you don't have any hills, the Vita Comp gearing would be great for you and you would not need to change it. I live in the Santa Cruz mountains, and no ride is flat and some are really steep. I learned about the gearing ratios from people on this forum because I did not understand them either. The cassette is on the back with 7-10 gears. The crank is on the front with either 2 or 3 gears. The smallest one on the front and the largest one on the back give you the low gear ratio. In my bike they are both now 28 giving a 1:1 ratio. If the one on the back is 30 and the one on the front is 25, it is harder to pedal uphill. If the one on the back is 26 and the one on the front is 32, it is so easy to peddle (granny gear) that it will feel like there is no tension and you probably won't use it much. You find this info in the technical specs on the website for each model. I still would ask for the skinnier tires, though. It makes it act more like a road bike with the easier to ride position. It's a really comfortable bike and goes quite fast.