I once made a point of inspecting closely my seat height each time my mph went down for a specifically known route. Lately tho my seat height was perfect but my speed was off by 3 to 4 mph – so I attributed it to wind & extra fatigue. Turns out I had worn out the essential inner-cylinder of my bottom-bracket – I actually have been riding forcefully enough to have bent it. This increased friction was slowing me down – not that I’ve been complaining.
Still, it’s good to know the reason. My Bike Doc has a good laugh at my stubbornness.
My old Tuesday-Thursday route today in the wind.
181 on the flats with only 15 mph to show for it drove me to inspect my front crank.
Ecbatan 