Could Nitrogen Offer Retreading Benefits?

In this column SA Treads editor, Liana Shaw, explains why nitrogen inflation could offer little-known benefits to retreaders.

It is probably no secret by now that I am a fan of nitrogen in tyres. I have spoken with too many fleet operators who swear by the cost-saving benefits of running on nitrogen, not to be a believer. I have also been using nitrogen in my own car tyres for over a year and enjoy not having to check tyre pressures every time I fill up. Unlike the inconvenience of running on air, which tends to escape from tyres at a rapid rate, the composition of nitrogen gas – which is characterized by larger molecules – substantially reduces the rate of emission. Then take the heat factor, long acknowledged as a tyre’s biggest enemy. Being an inert gas, tyres inflated with nitrogen run cooler, thereby prolonging tyre life. So far, so good. But could nitrogen’s properties and unique features extend further so as to be able to render valuable assistance to the retreader? The experts seem to think so.

One of the biggest challenges retreaders face is securing the best possible casings that will give credit to their retreads. Casing failures make their retreads look bad, which is why most people believe the casings they see on the side of the road are retread failures. Ironically, they seldom are. Around 90 per cent of them are casing failures caused by oxidation of the casing as a result of one thing, and one thing only – air inflation.

– When air is compressed the moisture content in a given volume of air is compressed into a smaller space, creating what is known as condensate.

– When the compressed air in a tyre is heated and cooled, even more condensate forms. This condensate and hot oxygen oxidizes not only the rims, but the whole casing from the inside, starting with the inner liner of the tyre. Oxidation of the inner liner can be seen with the change of colour and texture of the rubber from black and flexible, to grey and harder over time. As the aging process continues, the rubber hardens and fine hairline cracks start appearing in the inner liner with the flexing of the casing as it rotates.

According to Rob Sowry of Nitralife, every retreader knows this to be true. When the cracks start, not only does the aging spread faster through the casing, accelerating pressure loss, but the casing generates more heat through greater flexing, all of which speeds up the final break down of the casing. This is commonly known as a ‘Casing or Belt Separation”.

With the national average at about 1.8 retreads per casing, we know each time a casing is retreaded it becomes more likely to fail, (usually a belt separation). The primary cause of this is oxidation, as a direct result of air inflation. So what happens when air is replaced with nitrogen?

Nitrogen is free of oxygen, is inert and completely dry. It does not attack rubber and is the slowest migrating gas in the air. There is no oxidation of inner liner or tyre resulting in stronger, longer lasting casings. On top of this, slower migration which equates to better pressure retention.

By way of endorsement, Aberdale Cables had this to say: “Towards the end of 1998 we experienced a very high rate of blown tyres. After conducting a full investigation, including a tyre survey and blaming the tyre suppliers for bad quality, we discovered the problem. On each and every incident of tyre failure, the tyre casing had been retreaded five or six times. We find this fact almost unbelievable, as our very best before nitrogen was three retreads per casing. We have subsequently backed off our retreading process to four retreads.”

“If a retreading company wants to achieve the maximum number of retreads per casing, they should be promoting nitrogen inflation,” said Mr Sowry. “At the very least, this would give them a better tyre casing on which to risk their quality retread and reputation.”

He added: “It is not too late for retreaders to halt the gradual decline of retreading worldwide. I believe the situation can be turned around by accepting nitrogen as their ‘best friend’.”