nitrogen tyres.

[taylor]

the wife,y bought some tryes for the car they have filled them with nitrogen, any reason why, ? only a fiver,

[DryRob]

No realworld benefit apparently...

http://www.theaa.com/motoring_advice/safety/filling-tyres-with-nitrogen.html

[chaz]

mobile tyre fitters used to use nitrogen, easier than having a petrol compressor to inflate them

[Farjo]

Perhaps tyres will end up with almost 100% nitrogen after a while and here's my theory. Buy a new tyre which is filled with normal air (78% nitrogen, 21% oxygen). Some of the oxygen permeates through the tyre so you re-inflate it with air. Assuming the tyre pressure went down by 10% the tyre is now filled with the original 78% Nitrogen and 21% Oxygen, minus the lost 10% oxygen, plus the replaced 7.8% Nitrogen and 2.1% Oxygen = 85.8% Nitrogen and 13.1% Oxygen.

Repeat several times and the proportion of Nitrogen will steadily rise, not to 100% but presumably into the high-90s%.

[jon]

Why does only o2 permeate through the tyre, and not nitrogen?

[positron]

Molecular size perhaps?

[Lawrence]

It's something to do with nitrogen expanding less with heat, so the pressure stays more constant.
 
It might make a difference in F1, but in a road car?  Probably not.

[Jamieg285]

the wife,y bought some tryes for the car they have filled them with nitrogen, any reason why, ? only a fiver,

So that someone can make money for no real reason.

[JZS 600]

I used to be a trimix diver, don't fill your tyres with helium 

[jon]

Send her over here and I can replace the air for fresh for only a quid... probably needs doing weekly