TYRES: Expert advice

By: Steve Skinner


Good bus tyre selection might seem like commonsense, but experts say it’s often lacking

TYRES: Expert advice
Luke Hardy, Technical Manager for the Bus Industry Confederation

Sometimes the huge choice of tyres on the market and the long list of things which need doing to look after them must get a little overwhelming for bus operators.

So to help make their hard-pressed lives a little easier, the Bus Industry Confederation (BIC) is looking at putting together a technical Advisory on tyres and wheels.

Tyre life is always a big economic issue for any bus operator, but safety concerns are also prompting consideration of the Advisory.

For example, in the past couple of years there have been several fires occur due to a driver being unaware of a blown inside rear tyre, which has generated extreme friction on high-speed trips.

"Blown tyres have been both an ignition source and fuel for a number of fires," Technical Manager for the BIC, Luke Hardy says.

"It’s not necessarily been under-inflation or a fault, the tyre could have run over something," Hardy says.

Hardy expects a proposal for an official Advisory on tyre tips to be put before the BIC Council within the next few months.

The Advisory would involve considerable input from likely users and become an agreed but voluntary industry position on a wide range of critical issues such as recommended pressures and monitoring, rotations, alignments and re-treading.

"The key is to achieve minimum tyre costs but still have a safe and reliable bus fleet," says Hardy.

RULES FOR RE-TREADS

Luke Hardy is a bus industry veteran. A mechanical engineer by trade, he was with the New South Wales State Transit Authority (STA) for 17 years and manager of engineering policy and standards at the STA before a five-year stint as engineering general manager with Custom Coaches.

He is now Managing Director of Bus and Coach Solutions, consulting to both operators and suppliers.

Hardy has seen tyre standards improve ‘dramatically’ in his time, and says one of the key developments has been improved retreadability, without jeopardising safety and reliability – when done properly. Hardy adds that retreads can never be as good as cleanskins.

"Retreadability is a major part of cost minimisation," he says. "The tyre case needs to be so designed and manufactured to be able to be re-treaded two to three times.

"Typically new tyres are used on the steer and re-treads on the rear.

"If you assume that a new tyre will get around say 65,000km on the steer axle of a bus, and on the rear axle the retreads get around the same life per retread, then two retreads per case on average gives the operator sufficient stock of tyre cases and they should not need to use new tyres on the drive of the bus."

Hardy says tyre prices vary dramatically, but a typical new tyre might cost around $500, with each retread costing "a couple of hundred bucks" after that.

He says it should all be about total tyre life, which inevitably means forking out more upfront to save money in the long run.

POPE'S ADVICE

Michael Pope owns and runs the Michelin Service Centre at Ingleburn in Sydney’s south west. He looks after several big bus fleets, including a portion of the NSW State Transit Authority buses.

Pope points out that even though city bus tyres are made with thicker sidewalls than truck tyres, they are still highly vulnerable to kerb damage.

"We find bus operators need to rotate more often, especially on the left-hand side," Pope says.

"We see a lot of tyres that come back and the main problem is where the driver just keeps clipping the gutter, so they keep hitting the sidewall of the tyre. So the tyres are not worn out, but they have worn the sidewall out.

"Our main advice to bus operators is to try and regularly rotate those tyres, because they’re only getting half the life out of them," Pope says.

"So we’re saying turn them inside out, or go from side to side on the drive and side to side on the steer."

Of all the tyres on a city bus, one has to feel most sorry for those left-hand steers.

Not only are they often hitting kerbs, but because roads are cambered towards the gutter, they are constantly being powered uphill and to the right under acceleration.

The experts say that’s an example of the importance of front camber and toe alignments.

PUMPING YOURSELF UP

Many industry tyre specialists caution against the practice of over-inflation. For example rear tyres might be pumped up to 110psi, but the bus might run full for only one or two hours a day, so 90psi instead would avoid wearing out the centre of the tread.

Meanwhile American tyre company Goodyear is trialling self-inflating tyres in commercial vehicles, including buses, and hopes to have them available in Australia soon.

A thin tube runs around the inside of the tyre, and is connected to a valve open to the outside air which sits below the tread.

Air is let in or out of the valve and tube depending on the tyre pressure, which is monitored by internal sensors.

"Optimum tyre pressure is key in the commercial market," says a Goodyear press release announcing the trial last year.

"It is estimated that for every 10psi (70kPa) lost in tyre inflation, there is a 1 percent loss in kilometres per litre."

Goodyear also estimates that tyres which are under inflated by just ten percent, decrease tread life by 9-16 percent.

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