Nitrogen tyre pressure's
Discussion
I reckon the only reason to run N2 in your tyres is having a bottle/regulator/inflator somewhere you're going to have to bugger about with your tyre pressures. My mate does this for his "Down to 10PSI and then back up to 20" for trialling his jeep, saves half an hour on the electric pump.
I think that this is probably the reason for most people running nitrogen, I can't really see the 1/5 O2 being significant enough to cause any significant deviation. Oxidation of delicate rubber compounds may be a problem but I would have thought a slick/racing tyre was made of a pretty mundane carcass really.
It sounds like another way of getting your bucks off you. Running hydrogen or helium could be a way of reducing weight but then leakage would be a snag, you could use a teflon rubber inner coat but with hydrogen, would then form the rather nasty HF. Which would sod up your nice magnesium rims.
Hmmmm, not convinced, Stu
I think that this is probably the reason for most people running nitrogen, I can't really see the 1/5 O2 being significant enough to cause any significant deviation. Oxidation of delicate rubber compounds may be a problem but I would have thought a slick/racing tyre was made of a pretty mundane carcass really.
It sounds like another way of getting your bucks off you. Running hydrogen or helium could be a way of reducing weight but then leakage would be a snag, you could use a teflon rubber inner coat but with hydrogen, would then form the rather nasty HF. Which would sod up your nice magnesium rims.
Hmmmm, not convinced, Stu
It's the water in the air that causes deviation from the ideal gas law pV = nRT... if you know the pressure of nitrogen at ambient temperature then you can predict fairly well what it will be at the tyre's operating temperature. If you use air, the water in the air doesn't behave much like an ideal gas and the pressure in the tyre changes a lot less predictably with temperature.
D_Mike said:Yep. It's the fact that bottled N2 is far drier than air. There is an issue with using 'cold' pressure settings though. As stated above, tyres don't get too hot in normal road use, they do get a bit warmer though. 'Cold' pressures is a pressure known to produce the best running pressure once the tyres are up to temperature. The best way to find out the running pressure is to set the correct 'cold' pressures then drive the car to get normal warmth into the tyres. Run on for 15 mins or so to let the air pressure stabilise, then check the pressures. What you read will be the pressures required for N2 inflation, usually 2 or 3 psi higher.
It's the water in the air that causes deviation from the ideal gas law pV = nRT...
One thing often forgotten about is that using air has the added advantage of creating higher pressures when the car is being driven fast or vigorously. This advantage is lost if you inflate with dry gas.
Put simply the only real advantage to using dry gas is that your tyres will be at driving pressure even when cold. With me that is the first 15 miles, after that air would be better than N2 because it will change the pressures in a way that assists different driving styles.
Bottled N2 is dryer than atmospheric air, I'm yet to be convinced as to why that would make it a more appropriate gas for inflating a road tyre though. Dry air is availabe by the bottle and, I believe, is cheaper than N2. Its also pretty easy to dry air in situ as anyone who works in an air-conditioned office can testify.
I've just had a look at a Z=PVm/RT vs P plot for real gases and the Z value for an ideal gas is 1. Nitrogen gives a pretty linear response at about 0.99 whilst oxygen goes down to about 0.97 in a non linear fashion. Since a mixture would contain about 80/20 N2/O2 you could say that the response would be about 0.99 to 0.98 typically. This is pretty indicative of predictable behaviour if you ask me. I'd expect any deviation to be down to the presence of water, but in the absence of any suitable data, a bit of noodling would suggest that at tyre temperatures the amount of vapour is not significant to change the overall Z value. Hence I think it's all bollox.
Bollox it probably is. I see this as a bit 'max power'. Spoilers do make a difference but not with regard to your average Corsa. N2 does make a difference but not for you average road drive.
As I discovered by measuring tyre pressures after a hot 20 mins at Croft. With air my tyres measured between 3 and 5 psi higher than set cold prior to going on track. I believe with a dry gas there would have been less pressure increase.
For the road it's just not worth doing. You'll never get all the moisture out anyway.
As I discovered by measuring tyre pressures after a hot 20 mins at Croft. With air my tyres measured between 3 and 5 psi higher than set cold prior to going on track. I believe with a dry gas there would have been less pressure increase.
For the road it's just not worth doing. You'll never get all the moisture out anyway.
Bomber Denton said:
For the road it's just not worth doing. You'll never get all the moisture out anyway.
Especially as the tyre would have a degree if natural air in it already before inflation
you could easily just purge it a few times though (ie inflate it once with N2, let gas out, repeat twice).
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