Paul B wrote:And yes I understand where you are coming from 2wheels... at the end of the day it is the hours in the saddle and the accumulation of ks at a consistent rate that count.
What I'm trying to say is that there a lot of factors that can affect average speed on a long ride that you have little control over - wind speed and direction, whether you're at the front or the back of a group, and if so, how hard the group is going, the road surface, so on and so forth. The 'best' metric of performance we have is power, but obviously that's out of the price range for the average social cyclist to obtain. A higher sustained average heart rate for a longer period of time is another good measure, especially looking into heart rate zones, etc. There are plenty of books on how to train with these tools - Chris Carmichael and Joe Friel's works are generally considered good places to start. Times up a long sustained climb (15-20 min or longer) on different days are another basic metric you can use, as wind has less of an effect, and most groups generally split so you won't gain any aero advantage from sitting at the back.
Base time in the saddle's always a good place to start training wise though, especially for events like 100k+ sportives.