I have only one bike with two choices of rear wheels. For the bike path or riding around town for errands, the cassette is 13 - 26 for mostly flat routes. This wheel also has a rougher duty tire to stand up to clam shell on the bike path. For longer rides in outlying areas and where there may be steeper hills, the cassette is a home made 13 - 30. On the recommendation of Barrettsv, the chain rings are 50, 39 and 26. I don't need the 26 ring often but toward the end of a long ride when the legs are near their end, I'm very glad it is there. I use the same bike to tour with 25 pounds loaded on the back. During a tour, even if a hill is doable in higher gears, I make an effort to spin in the 26T ring which is better for long term endurance. As has been said, use the tool that works best for you.