Nearly 50% Of Cars Could Be Wasting Fuel Because Of Underinflated Tyres

A survey by the AA has found that 48% of cars could have underinflated tyres, meaning nearly half our private vehicles could be wasting fuel and compromising safety.

The survey results are published in the latest AA Directions (Winter 2010) magazine.

The results follow an earlier test by the AA where the Association found that driving with tyres 7 psi underinflated increased fuel consumption by nearly 8%.

AA PetrolWatch spokesperson Mark Stockdale says that after the test proved that underinflated tyres really do use more fuel, the AA wanted to know how many people might be driving on them.

“We thought there would be quite a few people with underinflated tyres, but we were surprised to find that it could be as high as half our private vehicle fleet,” he says.

“Underinflated tyres use more fuel and wear out faster, so they unnecessarily cost you money on both fronts, and they’re less safe.

“It’s like riding a bicycle with flat tyres. The effort you need to get a bicycle with flat tyres moving is far greater than if the tyres are properly pumped up.”

The AA survey involved a random sample of 150 vehicles undergoing a warrant of fitness at an Auckland AA Inspection Centre.

Forty-eight per cent of the vehicles had underinflated tyres and only 17% had tyre pressures at or within 0.5 psi of the manufacturer’s recommendation.

The average variation was about 4 psi underinflated, although several were out by double or more than this amount. One vehicle was 13 psi underinflated, at nearly half its recommended setting, and another was nearly twice the recommended air pressure, both seriously compromising safety.

Overinflated tyres wear unevenly, have less grip on the road and can affect braking ability. Underinflated tyres wear more quickly and affect cornering, braking and water dispersion, as well as increasing rolling resistance.

A vehicle with tyres 4 psi underinflated could be using about 4% more fuel1. At current petrol prices this equates to about 7 cents more per litre and over a year would add about $100 to the annual fuel bill for the average motorist in a medium-sized petrol car2, says Mr Stockdale.

Energy Efficiency and Conservation Authority (EECA) chief executive Mike Underhill says keeping tyres pumped up is one of a number of easy and free things motorists can do to minimise fuel wastage.

“It’s impossible to know exactly how much fuel we’re wasting, but the AA’s test gives us some indication. If the survey is typical of the national vehicle fleet then as a country we could be spending nearly $130 million3 more than we need to on fuel each year.

“We’re all concerned about rising fuel prices, but New Zealanders can effectively cancel out some of this year’s fuel price increases for themselves by checking their tyres at least once a month when they visit a service station.

“Correctly inflated tyres are a triple win for motorists because it reduces fuel wastage, reduces wear and tear on tyres, and it means you’re safer on the road,” Mr Underhill says.

AA tips:

For more fuel saving driving tips see www.aa.co.nz and www.energywise.govt.nz

For more information about AA fuel-saving tests see: http://www.aa.co.nz/aadirections/driver/pages/fuel-myths-exposed.aspx

For more information about the AA survey of 150 vehicles see: http://www.aa.co.nz/aadirections/driver/Pages/Tyre-pressure.aspx

1 This assumption is based on the results of the AA test which showed a vehicle with tyres 7 psi underinflated used 8% more fuel.

2 Based on $1.76 per litre of 91 Octane. The AA estimates the average car travels 14,000km a year and uses 10.32 litres of petrol per 100 kilometres.

3 Figure based on 48% of the light vehicle fleet, which is estimated at 2,631,014 passenger cars and vans (excludes motorbikes and commercial vehicles), multiplied by estimated extra annual fuel cost of $100. Estimates depend on the price of fuel, which fluctuates.

ENDS

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