I have a Giant Bike and am training for a road ride across Iowa (ragbrai). The ride will have 21,000 of climbing; fifteen thousand in the first two days. I am struggling when I am climbing in the bay area, mainly in Marin by Mt. Tam is where I ride. My cadence drops when I climb, and often I have to stand up to keep my bike moving uphill.
I have a standard crankset (ultegra, with two cranks, one with 53 teeth, and one with 39 teeth). My rear cassette is 12-25. I've gotten strong by riding a lot recently, but perhaps I should change my crankset or cassette to make climbing easier. Suggestions?