Quote Originally Posted by SadieKate View Post
The same 33 mile ride ridden over the years has gone from a 2.5 hour effort to a fairly consistent 2 hours. Why wouldn't this be a measure of my fitness?

It is the perfect measure of your fitness.

The same course, in similar conditions, repeated at intervals over the year (or measured at intervals over the year if you ride it often).

Half an hour is excellent improvement!