Motoring Discussion > Winter tyres pressures (sorry)	Miscellaneous
Thread Author: Rudedog	Replies: 24

Sat 9 Dec 17 11:12   Winter tyres pressures (sorry) - Rudedog

Due to work today is the only opportunity for me to do the families three cars tyre pressures. The temperature today will be around 1 degree, shall I stick with the normal indicated pressures or knock a bit off? The fuel flap sticker only has one set of values regarding temp. The difference I guess is very small so maybe just carry on with the same pressures. Reply to this message | Report message

Sat 9 Dec 17 11:24   Winter tyres pressures (sorry) - Clk Sec

I've tended to avoid checking tyre pressures during very hot or very cold weather conditions, but I've no idea if it makes any difference or not. Reply to this message | Report message

Sat 9 Dec 17 11:33   Winter tyres pressures (sorry) - bathtub tom

Checked mine the other day and they were all a couple of PSI low. I put it down to the cold weather and pumped them up to recommended pressure. Reply to this message | Report message       1

Sat 9 Dec 17 12:02   Winter tyres pressures (sorry) - Old Navy

>> Checked mine the other day and they were all a couple of PSI low. I >> put it down to the cold weather and pumped them up to recommended pressure. >> I did the same a few days ago, the pressures will drift down before the weather warms up enough to make any difference. Tyres run at higher than the recommended pressure when warmed by use anyway. Reply to this message | Report message

Sat 9 Dec 17 13:15   Winter tyres pressures (sorry) - CGNorwich

It’s Gay-Lussac’s law innit. Pressure of a gas at a constant volumis directly proportional to its temperature in degrees Kelvin. O level Physics Grade Passed Grade C Avogadro’s Hypothesis anyone? Reply to this message | Report message

Sat 9 Dec 17 13:43   Winter tyres pressures (sorry) - Cliff Pope

So if a tyre is nominally set at 30 psi, a change of say 10 degrees = 283/273 = 1 psi. Hardly worth bothering about? Avogadro - equal volumes of any gas at the same temperature and pressure contain equal numbers of molecules. Reply to this message | Report message

Sat 9 Dec 17 13:50   Winter tyres pressures (sorry) - Fullchat

Well whatever theory you throw at me, I had to put 3psi all round the other day. So I'm assuming that due to the drop in temperature :) Reply to this message | Report message

Sat 9 Dec 17 13:54   Winter tyres pressures (sorry) - Cliff Pope

+/- the errors in the two readings. But as soon as you start driving and the tyres flex the temperature will go back up again? Reply to this message | Report message

Sat 9 Dec 17 14:35   Winter tyres pressures (sorry) - bathtub tom

>> But as soon as you start driving and the tyres flex the temperature will go >> back up again? As they would in warmer weather, but as the ambient temperature is lower, the road surface temperature will also be lower. So the tyre pressure would probably not increase any more than it would in warmer weather. Reply to this message | Report message

Sat 9 Dec 17 14:41   Winter tyres pressures (sorry) - Fullchat

Good point. :) Reply to this message | Report message

Sat 9 Dec 17 14:46   Winter tyres pressures (sorry) - Old Navy

As tyre pressures are a average for average loads in average temperatures only an absolute anorak is going to worry about what the average should be at any given moment. :-) If my tyre pressures are low I top up to the recommended pressure, if high I leave well alone, they will decrease eventually. Last edited by: Old Navy on Sat 9 Dec 17 at 14:49 Reply to this message | Report message

Sat 9 Dec 17 15:56   Winter tyres pressures (sorry) - No FM2R

>> But as soon as you start driving and the tyres flex the temperature will go >> back up again? Presumably causing the tyres to expand and the pressure drop again? Presumably what the steel is there to try to prevent. Reply to this message | Report message

Sat 9 Dec 17 14:56   Winter tyres pressures (sorry) - CGNorwich

More or less. The situation is muddied by a tyre not being a rigid container and the gas volume not therefore remaining constant. I bet Mr Lussac's tyres were spot on. Reply to this message | Report message

Sat 9 Dec 17 16:12   Winter tyres pressures (sorry) - Ted

I drove to a local shop a couple of weeks ago. As I got onto the main road returning I felt the r/o/s tyre seemed to be on the rim. I stopped as soon as possible off the road and the tyre was, indeed, on the rim. I put 35 lbs in using my Fiesta pump and drove home...about a mile. Didn't use the RAV for a couple of days. I was surprised to see the tyre still 'up'. It stayed up for a couple of weeks until I got the pump ot at home and topped all 4 up. I put it down to the cold....but why only one ? Reply to this message | Report message

Sat 9 Dec 17 16:34   Winter tyres pressures (sorry) - Manatee

>> So if a tyre is nominally set at 30 psi, a change of say 10 >> degrees = 283/273 = 1 psi. >> Hardly worth bothering about? >> >> Avogadro - equal volumes of any gas at the same temperature and pressure contain equal >> numbers of molecules. > About one and a half Cliff Pope. You have to use absolute pressure as well, so your 30psi being the pressure above atmospheric is c. 45psi. If you set your pressures in summer at 25C, that could read 4psi lower when there is a frost. Reply to this message | Report message

Sat 9 Dec 17 17:12   Winter tyres pressures (sorry) - CGNorwich

But see above. There needs to be a constant volume to accurately calculate the effect of temperature on volume using that formula and a tyre is flexible and has a variable volume. Reply to this message | Report message

Sat 9 Dec 17 20:37   Winter tyres pressures (sorry) - VxFan

Isn't there an argument somewhere that nitrogen filled tyres are less susceptible to temperature variations than those filled with bog standard air? Reply to this message | Report message

Sat 9 Dec 17 20:42   Winter tyres pressures (sorry) - Bromptonaut

>> Isn't there an argument somewhere that nitrogen filled tyres are less susceptible to temperature variations >> than those filled with bog standard air? Given bog standard air is 78% nitrogen I'm not over bothered about other 22% Reply to this message | Report message

Sat 9 Dec 17 21:05   Winter tyres pressures (sorry) - zippy

>>Nitrogen Didn't some consumer program a while ago suggest that some tyre companies were selling nitrogen for tyres then inflating them with air, which of course as Bromptonaut said, they were getting 78% of what they paid for! Last edited by: zippy on Sat 9 Dec 17 at 21:05 Reply to this message | Report message

Sat 9 Dec 17 21:10   Winter tyres pressures (sorry) - Zero

>> Isn't there an argument somewhere that nitrogen filled tyres are less susceptible to temperature variations >> than those filled with bog standard air? I thought bog standard air was mostly methane Reply to this message | Report message       2

Sat 9 Dec 17 21:44   Winter tyres pressures (sorry) - Manatee

>> But see above. There needs to be a constant volume to accurately calculate the effect >> of temperature on volume using that formula and a tyre is flexible and has a >> variable volume. Quite true, but within a reasonable range it doesn't sound material? To the extent that it does,it would make the pressure difference smaller as you imply. Reply to this message | Report message

Sat 9 Dec 17 22:18   Winter tyres pressures (sorry) - Rudedog

Stuck with the regular pressures listed on each cars fuel flap. Of course will recheck when things warm up again. Reply to this message | Report message

Sun 10 Dec 17 00:07   Winter tyres pressures (sorry) - Hard Cheese

My BMW has tyre temperature and pressure display, as the ambient temperature drops so does the tyre temperature and so does the pressure. Of course road speed has an impact though I reckon the difference between summer and winter is around 3psi. Reply to this message | Report message

Sun 10 Dec 17 05:25   Winter tyres pressures (sorry) - Manatee

>> My BMW has tyre temperature and pressure display, as the ambient temperature drops so does >> the tyre temperature and so does the pressure. Of course road speed has an impact >> though I reckon the difference between summer and winter is around 3psi. >> Mine too, which is pretty much what you calculate for a 20 degree difference assuming no charge in volume. Reply to this message | Report message

Sun 10 Dec 17 08:03   Winter tyres pressures (sorry) - Cliff Pope

>> >> About one and a half Cliff Pope. You have to use absolute pressure as well, >> so your 30psi being the pressure above atmospheric is c. 45psi. >> >> If you set your pressures in summer at 25C, that could read 4psi lower when >> there is a frost. >> I hadn't appreciated that - thanks for the correction. So it does make a difference, assuming that the running temperatures maintain that differential Reply to this message | Report message