I typically do ~100km rides (almost always alone). In summer, I manage average speeds of 30km/h or more. This is the first (of only three in total anyhow) winter in which I keep riding somewhat regularly in winter.
I did > 1000 km per month in the summer months, and around 700km (some of which indoors) in the winter months (but extra running etc.). So I would expect my form and fitness to be somewhat lower, but not dramatically so. For instance, average watts on the indoor trainer as well as times when going running are fairly constant. (My PM also shows fairly constant wattage on the bike.)
Yet, average speeds are more like 27-28 km/h at the moment.
(In my case, although I hope the question could be of more general interest, I also ride a new bike which I had hoped would be faster although it is an endurance bike, simply because it is more high level in terms of the frame than my previous fairly entry level alu one.)
My question: Is that an expected decrease in speed? If so, is it possible to break down this difference into different components (next to, possibly, less fitness)? I think of
- typically more windy conditions, which hurts average speed
- more layers of and less aerodynamic clothes
- wider tyres (28mm insted of 25mm for me, also lower quality ones; also, the endurance bike maybe has somewhat less agressive geometry)
- more rolling resistance on wetter surfaces
- more careful riding style on wet surfaces (surely hard to quantify, but definitely applies to me)
- I heard something about colder air implying more resistance
- more energy needed to keep the body warm (although I rather overdress, I think)
- anything else?