Summer Breeze Blues and the Bearable Lightness of Winter?

nomdeboardie

So a few nights ago I was transporting myself a few miles down the road, then back a couple of hours later. There was a bit of a breeze, not sure exactly which direction, but things felt nice and 'light', on average, on the out journey. Expected to encounter a bit more resistance on the return, and I don't think conditions had changed much, but things felt better than anticipated. I then thought back to how I often felt the opposite way in summer - an oppressive [external breeze + relative movement] whoosh against me in most directions on many spins. Wondered if this might correlate with atmospheric pressure. Looked at an old-fashioned barometer when I got back, and sure enough pressure was low. OK, no further data yet , but the 'mean sea level pressure' figure at http://en.wikipedia.org/wiki/Atmospheric_pressure does suggest Ireland has lower pressure in winter. So those pesky air molecules are hitting me harder (higher temp.) and/or more often (denser air), on average, in summer as I propel myself towards them and, in a headwind, they're propelled toward me.

(In retrospect, a freak low pressure spell might explain the blissful week I once had when I just flew on both directions of my commute and I thought there must have either been a bizarre fortuitously-timed oscillation in wind direction each day or that I'd undergone a sudden inexplicable surge in fitness. I preferred to believe the latter, until things returned to normal and my illusion was cruelly dissipated, leaving me wondering if I had suddenly degenerated to my former level. :pac:)

Apologies if this is something everyone else already knows about (the 'lower pressure in winter'), or, conversely, it's codswallop (pressure difference not significant enough), but it does for the moment make me feel better about winter cycling. :eek::D

(By the way - anyone know if it's possible to get actual pressure readings from a Garmin Edge 500...? I currently have mine set to calibrate altitude from home, so I wouldn't even be able to infer anything from fluctuations in reported altitude.)

In general, aerodynamic resistance tends to be greater in winter. This is because the air is cooler and therefore denser at any given pressure.

That said, trying to measure aerodynamic resistance subjectively on the bike is fairly futile. There's far too many variables (terrain, position on the bike, wind, clothing, how many pints you had the night before, etc.).

cdaly_

Deleted User wrote: »

In general, aerodynamic resistance tends to be greater in winter. This is because the air is cooler and therefore denser at any given pressure.

Conversely though, since the air is cooler and thus denser, you can get more into your lungs in each breath and thus get more oxygen on board for more power.*







*Works for cars anyhow...

snailsong

I believe that in velodromes they keep the temperature very high 'cos it makes the bikes go faster.

nomdeboardie

Deleted User wrote: »

In general, aerodynamic resistance tends to be greater in winter. This is because the air is cooler and therefore denser at any given pressure.

That's actually what I assumed previously, but apperantly that's not the case(? open to correction with evidence contradicting the linked diagram and other things I read on t'internet today)

Deleted User wrote: »

That said, trying to measure aerodynamic resistance subjectively on the bike is fairly futile. There's far too many variables (terrain, position on the bike, wind, clothing, how many pints you had the night before, etc.).

Of course, but I'm just talking average perception (across all journeys, for a given season)

nomdeboardie

cdaly_ wrote: »

Conversely though, since the air is cooler and thus denser, you can get more into your lungs in each breath and thus get more oxygen on board for more power.*

I thought of the oxygen angle too, but as I said in my reply to JamesL85, I now realise that the air being colder does not necessarily translate to higher density or pressure (again, open to correction on that with further evidence)

nomdeboardie

snailsong wrote: »

I believe that in velodromes they keep the temperature very high 'cos it makes the bikes go faster.

Googles, has a quick look at http://www.bbc.co.uk/sport/0/cycling/17100619
- yes, they keep the temp up, but also acknowledge low pressure weather makes for fast times. I think that if the building were sealed the higher temp would actually increace pressure and air resistance.