[pastage]

I am not really contradicting you here. Just want clarification from GP. My reaction was Huh? As well.

With N=15 years of gps data and 40-70 of those days per year below zero very few below -10°C. I can say that I ride slower on cold days on avarage.

I am not fit and do not track that at all. I can barely keep my avarage above 25km/h in city traffic for 15km, very few conflict points maybe twenty but not comparable to road cycling. So a km/h decrease of avarage speed during winter is common but not a given. I do not count bad road conditions, but Stockholm has really good maintanance during winter, ice free asphalt all year.

[Lio]

I definitely ride slower in winter too but I always assumed that was due to my body having a harder time in the cold rather than air density changes.

That seems to be born out by using better (read more expensive) winter riding gear. I naturally run a bit cold so spending on low temperature tights, base layer and jersey/jacket has made a massive difference for me.

[LargoLasskhyfv]

More wind chill? More weight by thicker clothing?

[pastage]

I ride with heavy loads, 10+ kilos is common, no stats on that though. For my speed it does not matter much with 2 kg clothes.