I was out, having an evening potter last night, about 9.30pm. As you do.

Why is it, when you go from a tarmac’d road to an off road section (bridleway – no tree cover), that the air temperature is noticably colder?

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Tarmac absorbs the heat, simples 🙂

Cos the road absorbs more heat than the bw, and is releasing that stored heat once the ambient temp has dropped. Or something

ta, for the replies, i thought it would be something like that.

why does tarmac retain heat better than hard pack? or am i missing something super simply and being dumb…

Largely because it’s black I imagine…

Black has the highest coefficient of absorbtion; also I suspect a smooth surface probably increases it too (but not sure about the latter). Also, the tarmac will be closely and densely packed whereas the bridleway is unlikely to be (but haven’t done a check on your bridleway!!.

Absorbs heat because it’s black (awaits Ali G joke).

Retains it due to mass/specific heat capacity.

Releases it due to colour also.

I remember when i was a youth and we would hang around outside like you do on a very cold night. Someone said ‘why is this iron railing freezing cold yet this wooden one is quite warm’ to which I replied ‘they are both actually the same temperature although as the iron railing has a higher heat capacity it is absorbing the heat from your hand at a faster rate and therefore feels colder to your touch’. I was swiftly called a nob and no more was ever said of the matter.

There is probably moisture just under the surface of the dirt too, which would be or have been evaporating through the day through the surface, also helping to chill it. Just guessing but it’s plausible.

Also, was the bridleway in a dip or trough? Cold air gathers in these, of course.

they are both actually the same temperature although as the iron railing has a higher heat capacity it is absorbing the heat from your hand at a faster rate and therefore feels colder to your touch

Higher thermal conductivity, not heat capacity.

On a similar tack – why, when there is not a hint of wind in the trees does it feel like I’m riding into a headwind on my road bike?? (And not just when I’m knackered!)

Dez – the majority of your energy is spent moving air out of the way & the faster you go, the harder it gets. The moving air feels like wind as you move through it.

Probably….. 🙂

Surely it’s just cooler to ride a mountain bike off road than on road

Cos the road absorbs more heat than the bw, and is releasing that stored heat once the ambient temp has dropped. Or something

And apparently that’s why you should be careful while driving at night in Namibia: all the donkeys go and sit on the road to stay warm overnight, and then get run down by careless drivers.

[/random useless facts]

I don’t think I go fast enough for that, woody 🙂