86% of all Cars Involved in UK Road Accidents have Incorrect Tyre Pressures. – February 11th, 2015

Tyre pressures are critical as the footprint of a tyre is the only contact a vehicle has with the road. The only control you have is dependent on that foot print operating the way it was designed to which means, at the correct pressure. Most people are well aware of the fact you are supposed to check tyre pressures regularly but how many of us actually do? You’d be surprised at some of the results road checks uncover.

Sussex Police force, in the United Kingdom, carried out a roadside survey to check tyre pressures due to their concern with incorrectly inflated tyres. The check allowed a +/- 5psi tolerance against recommended handbook pressures.

The results of the survey were that 73% of all cars checked had incorrect pressures.

Police also check the tyre pressures of every car involved in a road traffic accident in the UK. This data shows that 86% of vehicles involved in road traffic accidents have incorrect tyre pressures.

Furthermore, tyres that are under inflated by just 20% (4-6 psi) on average can lead to your tyre lasting 26% less than it would correctly inflated. According to police figures 73% of tyres checked were 5 psi out against handbook pressures.

It is estimated that under-inflation of 20% can cause fuel costs to rise by 5%.

The simple answer therefore is that Nitrogen inflation can save you money and keep you safer on the road.

How does Nitrogen save money and make you safer on the road?

Compressed air contains Oxygen and Nitrogen in roughly a 20% to 80% mix. It does however contain other gases as well as water, water vapour and dirt / grease.

Certain components namely Oxygen, water vapour and free water that are found in compressed air are prone to permeation through the tyre structure. This is not from faulty valves or leaky rims but a natural pressure loss across the tyre and into the atmosphere. The wall of a tyre may seem solid but it is in fact a “Permeable Membrane” meaning gases can pass freely across it. Tyre manufacturers coat the inside of a tyre with a Butyl liner to slow pressure loss but it is not a cure.

Of these components in compressed air, both water vapour and free water can enter the tyre in varying amounts even if identical tyres are inflated with the same gauge on the same day. Compressed air is not a specified gas and as such will always contain varying amounts of these components that are not suitable for tyre inflation.

In tests, that 20% Oxygen / 80% Nitrogen mix changes to a 10% / 90% mix in a tyre that has aged and not been topped up recently. This demonstrates that the oxygen is leaving the tyre cavity faster than the oxygen so why not start with a higher Nitrogen concentration to begin with? It is true to say that regular tyre maintenance negates the need for Nitrogen inflation but unfortunately, a huge majority of motorists don’t do this resulting in under inflation.

Under inflated tyres create drag which increases tread wear, fuel costs and the risk of punctures as well as having a significant effect on a cars performance both in handling and cost. By having your tyres inflated with nitrogen this produces a stable inflation mixture, as can be seen in the diagram below, that has improved pressure retention properties that will ensure tyres remain fully inflated for longer.

By having your tyres at the correct pressures you will experience the following benefits:

1. Better handling and road holding
2. Reduces tread wear and increases tyre life by up to 25%
3. Correct inflation pressures reduce puncture risk by up to 33%
4. Reduced rolling resistance improves miles per gallon by 2%

Nitrogen tyre inflation is not a new concept. Nitrogen as a tyre inflation medium has been around since the early 70’s and has been used in applications which require safety or performance. The earthmoving industry use Nitrogen to prevent latent heat build-up as Nitrogen does not heat up as much as compressed air when a vehicle is in motion. Similarly, there is an Airworthy Notice posted to say that all aircraft must have a minimum 95% Nitrogen in their tyres. This was issued following 3 aborted take offs by an air Mexico flight, cause so much heat in the tyre that when it was retracted into the undercarriage the combination of heat and oxygen cause the tyre to explode.

Formula 1 Grand Prix racing have used Nitrogen for decades as the tyre pressures are so critical and nitrogen is a dry, inflammable gas. Standard compressed air, contains 78% Nitrogen, 21% Oxygen and 1% other gases. It also contains water, both in free form and as vapour. At tracks like Monza, the tyre cavity can reach temperatures of 180 degrees centigrade and at this temperature water can expand to 1000 times its original size, greatly increasing tyre pressure. As there is no control over how much water enters the tyre a driver would have 4 tyres, at various different pressures, while doing close to 200 miles an hour.

For the majority of general motorists, Nitrogen inflation machines provide a solution to the gradual pressure loss which requires air top ups every 2 weeks, and will maintain the correct pressure, correct contact patch and provide safer and more cost efficient motoring.