old_windbag wrote:squeaker wrote: ChrisButch wrote:
One of the factors here, I think, is the air pressure. Freezing winter weather usually means high pressure, ...
Plus cold air is markedly denser than warm air....
Interesting ... I'd never thought before about the effects of temperature and barometric pressure on air resistance. Actually in typical UK weather conditions, temperature will have more effect than pressure. Density is proportional to P/T, where P=pressure and T=Temperature (degrees Kelvin). At sea level P will typically be between, say, 980-1030 mbar - or very roughly a 5% range around the mean. Temperature will typically be between, say, -3 C and 25 C (270 and 298 Kelvin) - or roughly a 10% range.
But if you live in a very hilly area, the pressure will be very roughly 5% lower at 400m than at sea level - so the potential variation due to air pressure (sum of meteorological and altitude effects) will be around 10%.
(Of course both temperature and pressure in the UK is occasionally outside these limits, and there are a few cycle routes above 400m too.)