I run 175/65/R15 winter tires on my 2nd gen Insight, and they are a bit narrow and small for a car of that weight; other lighter cars often have way fatter tires, even as OEM.
So all the more reason to keep the pressure up way above factory recommendation
(2.4 Bar, while I run them at 3.2 / 46 PSI.)
Or so I thought.
The last few weeks we had a cold spell here; Siberian wind 6 Bft dead east. down to -9 Celsius all day.
I found my car to be somewhat loose on the shoes. Wind sensitive, prone to not corner as tight as I'm used to. Also, it was not as economical as I expected it to be, even taking the cold into account.
As I was about to embark on a long trip I decided to check the tire pressure never mind the cold. And lo and behold, they were down to 2.6 Bar all round...
Upped them to 3.2 Bar again.
Now that was funny. I swap my tires myself. They've been stored all summer and held their pressure. The dealership lowered them at MOT, but I put them back up soon afterwards and expected them to stay there.
But that was on a lukewarm autumn day, and this was the coldest day in 6 years. I know the cold drops tire pressure, but this much?
Time to do the math.
I filled them to 3.2 Bar at 17 degrees Centigrade, that's about 290 degrees Kelvin.
I checked them at -9, that's 268 Kelvin.
3.2 bar tire pressure is actually 3.2 bar overpressure compared to the outside air, so it is 4.2 bar combined.
The tire pressure should be ((1 + 3.2) / 290 * 264) - 1 = about 2.8 Bar at -9 degrees Celsius.
Yup, I should have lost 0.4 Bar or almost 6 PSI due to the cold.
Another 0.2 Bar or 3 PSI went south for no reason whatsoever.
Yet most of the loss was due to the cold.
Anyway, after I raised the pressure again the economy gained considerably. And as the wind has changed and the frost is gone, the economy gets better still; almost summerlike.
Best of all, it grips the road really good; sharp steering and confident cornering. There's more road noise and vibration though.
Better not check the pressure now again or I'll see numbers I haven't seen before on car tires
We also had some snow. I was wondering whether the high pressure would impact grip in the snow negatively, but it did not. On the contrary, really.
Then, we also had snow just after its MOT whereat the monkeys had lowered the tire pressure; at that time it seemed to have very low grip...
I know you need to lower tire pressure in loose sand, but snow seems to require high pressure?
So, check your tire pressure when it gets really cold.
Also, wear gloves if you can while doing that. I did not. My hands hurt when I think of it.