Check out many rides in the mountains of NC. I was in a group of 50 people in the HHH last year, and me and one other guy were the only ones not walking our bikes up Bearwallow Mountain. It was not 3 miles or 15% either. Beech Mountain will get you attention as will Brasstown. The Assualt on Mitchell includes something like 7000 feet of climbing in the last 27 miles. Not everyone wants to do that with a 34-25. Some think they do, and end up walking or bowing out. Unfortunately many are told a 39-25 is fine.
Richard