Tyres "perishing"

Jamie_Carter

facade wrote: »

I'm no expert, but I would have thought that at the sort of temperatures & pressures used, both pure nitrogen and the mixed gases in air behave as ideal gases, and therefore would expand the same.
However, if there was water in the air mix there would be some effect as it evaporated and put more gas into the tyre.

The migration through the rubber issue, I really don't know.

Elf & Safety: I do know that passenger aircraft tyres use pure nitrogen as there is a low limit on the amount of oxygen they can contain in case the tyre catches fire, I've no idea about race regs.

But the conclusion is the same: A pure nitrogen fill on a road car tyre is a waste of money if they charge extra.

The reason to use nitrogen is because unlike air, the pressure doesn't increase/decrease with temperature changes.

There can easily be a 15 or 20 degrees C temperature differential between day and night, and this can be even more as temperatures can increase due to high speed driving. This can cause a variation in temperature of quite a few psi. This can obviously be a safety issue. And with motor racing it can have a huge effect of grip and tyre wear.

On aircraft the temperature differential can be huge. For example a plane could take off in a very hot country with temperatures of up to 50 degrees C, but during the flight temperatures could be as low as -30 degrees C. If air was used then the pressure change would be massive, and the constant high/low pressure cycles could lead to premature failure of the tyres.

Jamie_Carter

colino wrote: »

Nitrogen, the next profit line for KF! If the tyre is mounted to the new wheel and attached to a vacuum pump to strip the air out and then filled from a 100% N tank, how much more beneficial is that to the garage airline, which will pump in fresh air, made up of around 79% Nitrogen?
They'll start charging for putting the cars on the lifts next.

It actually makes quite a big difference.

Jamie_Carter

colino wrote: »

So if the newly fitted tyre already has most of its volume filled with good old fresh air (79% N) when you increase the pressure with this stripped air, there really isn't a whole lot of difference in percentage terms of the amount of nitrogen in the fully inflated tyre.

Yes there is.

If you took a huge balloon, and emptied all the air out of your tyres into the balloon, then the balloon would end up many times bigger than the volume of your tyre.

I don't know the exact equation at pressures of around 30 psi. But to give you a more extreme example, a 9 litre cylinder compressed with air up to 300 bar pressure, will hold 2460 litres of air.

colino

Well that's certainly an extreme example, as in entirely irrelevant, why not stick to Boyle's law and STP to keep it simple?

Jamie_Carter

colino wrote: »

Well that's certainly an extreme example, as in entirely irrelevant, why not stick to Boyle's law and STP to keep it simple?

It is entirely relevant. It gives an example of how air can be compressed many, many times. In this case 273 times it's original volume.

So it kind of blows your statement right out of the window.

GolfBravo

Jamie_Carter wrote: »

On aircraft the temperature differential can be huge. For example a plane could take off in a very hot country with temperatures of up to 50 degrees C, but during the flight temperatures could be as low as -30 degrees C. If air was used then the pressure change would be massive, and the constant high/low pressure cycles could lead to premature failure of the tyres.

What are you talking about? That's not why nitrogen is used in aircraft tyres.

Hint: moisture and ice.

colino

Jamie, I'll give you a clue why aircraft, with their very high pressure tyres and even with safety plugs, that are subject to explosive failure use nitrogen or helium to fill them - the bit about explosive failure.
Your belief that gases don't expand on heating, I'm just not sure if you made that up for the hell of it or not.

Ultrasonic

Jamie_Carter wrote: »

The reason to use nitrogen is because unlike air, the pressure doesn't increase/decrease with temperature changes.

That simply isn't true. As above, moisture is the significant difference, NOT the gas.

Jamie_Carter

GolfBravo wrote: »

What are you talking about? That's not why nitrogen is used in aircraft tyres.

Hint: moisture and ice.

Moisture does come into it, but what I described is the main reason.

Jamie_Carter

colino wrote: »

Jamie, I'll give you a clue why aircraft, with their very high pressure tyres and even with safety plugs, that are subject to explosive failure use nitrogen or helium to fill them - the bit about explosive failure.
Your belief that gases don't expand on heating, I'm just not sure if you made that up for the hell of it or not.

And what qualifies you to make that statement??

The main reason to use nitrogen is because it doesn't expand/contract as much when subjected to temperature changes. My father's 40 years as a ground engineer, and then a flight engineer, should make him far more qualified than you to know that.