Look, average speed is not very useful.
Cycling is very different from other sports in that no 2 exercise sessions are the same and it is very difficult to compare One cycle with another.
Wind direction & speed/terrain/weather/traffic lights/traffic density are all major factors when you are cycling.
IMO almost a feel you have when out as to what your level of fitness is.
For example I did an 80 mile ride this morning. I felt very good & I was making a good attempt at beating the wind and was making easy work of short inclines (today was a flat route for me). It's not nearly 8pm and I don't feel tired. My average speed was 14mph.
Today was a watershed for me so far this year. Up until now I have been feeling very tired after rides and feeling sluggish. On similar ride distances recently my avg speeds have been between 15-16mph. Last week I did an 80 mile hilly run. I have a feeling this broke me through to another level of fitness.
Today, the wind was blowing up to 20mph and at points I could barely hit 10mph when I was heading directly into it. On other rides,they have been hilly, have taken it a bit easier, took some wrong turns etc etc. See how useless avg speed is.
You have to learn to understand and listen to your body and I appreciate this comes with experience.
Try measuring some of the following (not in any particular order):
1. resting heart rate (so get a HRM if you don't have one. This is by far the best way to measure fitness)
2. maximum heart rate
3. Your recovery times.
4. Choose a few hills and measure the ease you climb them. "Ease" being the gear you are able to maintain and whether you can do some/all of the hill out of the saddle.
5. Try to get a training partner, ideally a similar ability or better. Measure yourself against them. See if you can improve the need for less drafting (i.e. hiding behind the other rider to stay out of the wind and save energy), compare hill climbing ability and how you fare over time.
6.Try a few TT's at a local club.
I'm sure others have different ways of measuring their improvements over time but a combination of the above works for me.
