Monitoring the tread is relatively easy – it’s right in front of you. But checking the pressure is less obvious – it requires equipment and getting your hands dirty. Many drivers just can’t be bothered.
Incorrectly inflated tyres can have significant consequences for safety – affecting the steering balance, braking ability and ride characteristics of commercial vehicles – and also cost, rapidly leading to excessive wear, premature replacement and decreased fuel efficiency.
RAC Foundation for Motoring figures indicate that 20% under-inflation increases tyre wear by 25%, reduces tyre life by 30%, and can result in a 3% increase in fuel consumption. More importantly, statistics from Renault show that around 6% of all fatal motorway accidents are caused by under-inflated tyres.
Currently, road tyres are filled with compressed air, which is composed of 21% oxygen, 78% nitrogen plus trace gases such as helium and water vapour. Although this method is most common, it raises a number of problems, as a tyre is effectively a membrane through which oxygen can diffuse, causing the tyre to deflate no matter how well it is constructed or sealed at the rim.
Engineering firm Parker Hannifin is one of several firms producing technology that enables the air in tyres to be replaced with a higher concentration of nitrogen.
‘Nitrogen-filled tyres remain at a constant pressure between vehicle services, because nitrogen molecules diffuse less easily through a tyre than oxygen molecules,’ explains David Wright from Parker Hannifin.
‘As a result tyres remain safe, costs are reduced through increased tyre life and fuel consumption is reduced. The problem of oxidation within tyres – natural deterioration of the rubber due to contact with moisture-rich air – which can lead to compromised strength and elasticity, is also eradicated, as the nitrogen compared to the compressed air is dry.’
Because of these benefits, nitrogen is already widely used for tyre inflation in aviation and motor sport.
But Wright says developments in the technology have made it a cost-effective alternative for wider commercial applications.
He says: ‘If the oxygen concentration in each tyre on a vehicle is reduced to 6.5% by introducing nitrogen, its partial pressure can be equalised to that of ambient air, thereby eliminating the force that would otherwise drive air through the tyre wall.
‘As a result, tyres filled with nitrogen remain at constant pressures and normally only require checking at standard vehicle service intervals.’
The latest nitrogen generation technology enables a normal stream of compressed air to be split into two component streams – one of oxygen, one of nitrogen. Specially-designed equipment fitted to a standard air compressor takes the separated nitrogen and purifies it, resulting in an overall higher nitrogen concentration by the time both gases reach the tyre.
‘These systems can achieve excellent results. They eliminate the need for expensive compressor upgrades or heaters, lower operating costs and increase system dependability,’ Wright says. ‘Furthermore, as there are no moving parts in the units, they are extremely reliable with very little maintenance required over their service lives.’
The latest nitrogen generation systems are already being used in the USA and in a number of European countries, including BMW garages in Germany and Volvo in The Netherlands. The benefits of nitrogen filled tyres are also endorsed by tyre manufacturers and a number of independent motoring organisations.
Wright says that one of its clients in the UK, industrial distributor James Lister & Sons, reduced its tyre costs by 15.5% through reduced wear over a 12-month period of running nitrogen-filled tyres.
But critics say that while the technical merits of nitrogen are well-founded, the practical gains to be had in everyday fleet life are not so clear.
Mike Wise, fleet sales director for Kwik-Fit Fleet, says the biggest challenge for fleets is to get drivers to check their tyre pressures in the first place.
‘If people check their tyres regularly in the proper manner, that’s all you will actually need to reduce costs from deflation,’ he says. ‘There is a technical argument that nitrogen would help, but you can buy your own mini-air compressors and fill tyres with air at garages.
‘Is it worth investing in nitrogen? Well, that invovles an additional cost and the likelihood of people using it is very slim.’
AA Tyre Fit dabbled in nitrogen a few years ago. More than 100 of its service centres used to offer nitrogen at £1 per wheel compared with about 20p for compressed air, but the group stopped offering it almost five years ago.
Today, various firms offer to fill tyres with nitrogen for between £1 and £2 per tyre.
There is little doubt that there are potential gains to be had – the technology works and tyres will not deflate as quickly. But with compressed air available for very little at garages – and in some cases for free – fleets will need to think carefully about the potential benefits before taking the plunge.
It could be that an effective system of checking pressures regularly is all that is needed to see savings on tyre costs.
Nitrogen pros and cons