Road trip coming up.

[euromodder]

Originally Posted by sbestca

I forget the exact numbers but nitrogen filling without purging puts the oxygen percentage down to about 5% and still significantly reduced the oxidation of the rubber in tires. In their testing they felt purging was good practice, but not essential.

Hence the fallacy of nitrogen fills ...
After say 7 years, the INSIDES of a tyre will still look and feel brand new.

You can't keep sun and oxygen away from the outside though, so tyres start to dry-rot and crack.

The actual material cost of nitrogen fill is so low that tires could be purged and re-filled for pennies at the next opportunity.

Yet everybody way overcharges for N2 fills ...

The study did a comparison of tires used in the Phoenix AZ area with tires baked and pressurized in an oven to compare test methods. The main effects of oxidation is hardening and cracking of the rubber,

Those are UV effects, i.e. sunlight.

Next time your tyres are off, have a look inside.
Unless you've been running on a flat tyre too long, they'll be pristine.

The "good" rear tyre on my Peugeot 306 had 100.000 miles on it, back in the day. The outsides were badly cracked due to sun exposure. The inside was totally pristine and smooth.
It was replaced as the other rear tyre was bust - I didn't bother to swap it when it went flat , I just drove it to the tyre dealer.

[sbestca]

Originally Posted by euromodder

Hence the fallacy of nitrogen fills ...
After say 7 years, the INSIDES of a tyre will still look and feel brand new.

You can't keep sun and oxygen away from the outside though, so tyres start to dry-rot and crack.

Those are UV effects, i.e. sunlight.

Next time your tyres are off, have a look inside.
Unless you've been running on a flat tyre too long, they'll be pristine.

The "good" rear tyre on my Peugeot 306 had 100.000 miles on it, back in the day. The outsides were badly cracked due to sun exposure. The inside was totally pristine and smooth.
It was replaced as the other rear tyre was bust - I didn't bother to swap it when it went flat , I just drove it to the tyre dealer.

Well, yes and no...

The sun and ozone exposure do cause cracking, but the rubber degades in other ways too.
Essentially it continues curing, getting harder and less supple. The prime factors in order are:
1) heat, especially over 200c
2) UV sun exposure
3) ozone, a more active form of oxygen
4) O2 oxygen, especially in combination with the other factors.

To protect from UV and ozone a thin layer of protectant rubber is applied the the sidewall before cure.
To seal air into the tire (natural rubber is surprisingly porous to gases) there is an inner layer of synthetic butyl rubber.
When you look at the inside of the tire this is what you see, the synthetic butyl rubber.

As the tire ages the rubber hardens, flexes less, has less traction and more readily separates from the cords.
UV and ozone start this process from the outside, where the damage is superficial.
Heat and O2 create their changes through to the center of the rubber, where cord debonding and failure are the risk.