Been in single figures the past few days in the Peak District. Tyre pressures all down by 0.2bar as a result. Thought they looked a bit soft but who can tell with low profile tyres. Hoping to improve mpg by pumping up back to normal.

Edited 19 October, 201015 yr by gregoir

The rule-of-thumb we always used was a 10degC change in temperature give at 0.1bar change in pressure. So if the temp drops from 20deg to 0deg then the pressure in the tyre falls by 0.2bar

What he said.

Air is classed as a semi-perfect gas which fairly closely follows the rules of a perfect gas where (P1 x V1) \ T1 = (P2 x V2) \ T2

where temperature is in degrees Kelvin ie Centigrade plus 273 degrees.

So as previous reply said a 20 degree temperature drop ie 7% roughly lower tempature will produce a 7% drop in tyre pressure ie about 0.2 bar or 3 psi or so.

Tyre should be ideally set at around 15 degrees centigrade known as NTP ie normal temperature or compensated accordingly if set at 25 C or 5 C ie adding or subtracting 0.1 bar.

I usually run my around half way between low and high load pressures even when on my own ie about 2.2 bar on the front and maybe 2.5 bar on the back on the TSI VRS and PD Estate but 2.8 on the back when loaded.

Edited 19 October, 201015 yr by lol

Is there a different rule to having them inflated with Nitrogen? My old man has been running his Almera on nitrogen filled and only had to have them topped up every 8,000 miles. He swears by it, but I've not tried it myself.

Quote from ATS website:

"All tyres allow gas to travel through the sidewall, which is why you need to regularly check your tyre pressures. Filling tyres with Nitrogen means that your tyre pressure will remain correct for longer because the rate at which Nitrogen passes out the walls of your tyres is slower than oxygen."

Is there a different rule to having them inflated with Nitrogen? My old man has been running his Almera on nitrogen filled and only had to have them topped up every 8,000 miles. He swears by it, but I've not tried it myself.

Quote from ATS website:

"All tyres allow gas to travel through the sidewall, which is why you need to regularly check your tyre pressures. Filling tyres with Nitrogen means that your tyre pressure will remain correct for longer because the rate at which Nitrogen passes out the walls of your tyres is slower than oxygen."

Well, air is 78% nitrogen, so I am a little sceptical of some of the claims for nitrogen-filled tyres. And yes, pressure will drop with temp in the same way with nitrogen as with air-filled tyres.

Perhaps we could ask to see ATS substantiation for that comment. Nitrogen's atomic weight is 14 compared with oxygen which is 16. I doubt there is any difference in the permeability of a tyre to these gases. OOxygen might be more prone to bonding to the tyre and decaying it however...

OK its more complicated than I thought - here is a paper, albeit from Acme Nitrogen Corp or similar!

http://www.getnitrogen.org/pdf/graham.pdf

Atomic weight isn't strictly linked to the size of the molecule (Oxygen and Nitrogen like to go round in pairs).

It seems to me that the benefits of Nitrogen in your tyres are pretty much wiped out by checking your tyres once a week.

In fact I'd say that it's arguably more dangerous putting nitrogen in Joe Public's tyres because they will then think they never have to check them again.

Nitrogen won't stop punctures.

Buy a pump

http://www.machinemart.co.uk/shop/product/details/12v-mini-air-compressor/path/vehicle-accessories

Tank of nitrogen not needed.

Buy a pump

http://www.machinemart.co.uk/shop/product/details/12v-mini-air-compressor/path/vehicle-accessories

Tank of nitrogen not needed.

I had one of those and it lasted one use. The thing was so badly made and put together it rattled itself apart. You can't beat a good old fashined twin barrel foot pump for that job!!