I guess it took me three years to finally realize how to use Cruzbike's aero advantage to keep up with my DF friends. I was slow to begin with, even before switching to S40. After switching, I just wasn't able to keep up with the rest of group climbing hills, even now in the 3rd year riding. Going downhills, I usually stop pedaling and try to take a break before the next climb. So the result is frequently I am just getting farther behind until they stop for a break for me to catch up. Thanks to @DocS, who mentioned in one of his posts that he usually pedals faster going downhills to get more momentum for the hills coming up. The light bulb went on, and I changed my riding style. Now I try to speed downhills to get more momentum going uphills or to pass the group before they pass me going uphills. So far it has worked well. I have kept up with the group most of the time for the past two rides!