Bridgestone South Africa

What Are The High Costs Of Low Air Pressure?

Why are you always harping on about proper inflation pressure?

Tyres are called “pneumatic”, from the Greek word “pneuma”, meaning “air, wind or breath”. And there’s a reason for that.

What supports your cargo is pressurised air, NOT your tyres. The tyre is just the container – that holds the air – that supports the load.

But why so much fuss about exactly the right pressure?

As mentioned before, the right inflation pressure can minimise many types of irregular wear. And that means higher removal mileages and reduced tyre handling costs. In other words, tyres last longer when properly inflated.

How much longer?

The Tyre Maintenance Council (TMC) reports that 10 percent under-inflation will shorten tread life by 9 to 16 percent.

If we use an average tyre price of R1000.00, that under-inflation costs you R160.00 per tyre. And, because you’ll change tyres more often, you’ll pay more in tyre service fees, along with downtime.

And how many drivers and maintenance people, if they had a target inflation pressure of 800 kpa, would consider 720 kpa (10 percent under-inflated) “close enough”?

What if the under-inflation is worse than that?

TMC suggests that each 10 percent results in a similar loss in tread life. So 20 percent under-inflation could cost you R320.00 per tyre. And if under-inflation exceeds 10 percent, you may have bigger problems. Like flat tyres and emergency road breakdown service calls that can cost anywhere from R200.00 and up.

In the USA, both the TMC and the Rubber Manufacturers’ Association (RMA) recommend that any tyre found to be 20 percent or more under-inflated should be immediately removed from service, demounted and inspected for damage.

What about duals?

As mentioned before, if the tyres don’t match in diameter, the smaller tyre is dragged along by the larger. This can result in extremely rapid and irregular wear on the smaller tyre. If duals differ in inflation pressure, their diameters can differ enough to cause this kind of problem.

Are wear and fuel economy the only losses?

They’re just the beginning. Imagine bending the sidewall of a tyre with your hands 500 times a minute. A truck tyre goes through a full revolution, flexing all the way around, about 300 times per kilometre. At 95 km/h – a kilometre a minute, that’s 300 times a minute.

Tyre engineers call this flexing “deflection”. With under-inflation, there’s even more deflection, consuming more energy and using more fuel. 

Are there any other losses as a result of under-inflation?

Unfortunately, lots of them. Remember what we said about “deflection”? Excessive deflection weakens steel cords excessively. And it’s accepted as a fact in the tyre industry that under-inflation is a major contributor to premature tyre removals.

But even if things don’t go that far, flexing can generate excessive heat, the enemy of tyre casings. Just as time ages people, heat ages tyres. And, if you’ve been accustomed to getting 2 retreads from each casing, you may discover that your average has dropped to 1,5. 

What would that cost?

If your casings are worth R300 – R500, instead of getting a useful retread, that is how much you could lose.

Why don’t you just make tyres that don’t leak?

Because the gas molecules in air are too small. Eventually they can diffuse through the rubber of a tyre, and escape into the atmosphere. This doesn’t happen quickly, but it means you can lose up to 30kpa per month through diffusion alone.

What can we do to prevent pressure losses?

Check pressure regularly. Use a good gauge, and calibrate it often. To keep air in, keep wheels clean and properly lubricated. And, make sure valve stems and cores are in good condition.

Finally, quality metal valve caps are a must. Caps are the primary seal against valve leaks, and also keep dirt and water out of the mechanism.

Why is that important?

A valve core is a mechanical device that must seal at very high pressures. If a tiny bit of dirt gets in, it can prevent proper sealing. Likewise, just as water can freeze and crack concrete, water can freeze inside valve stems, disrupting the seal.

But it does cost something to check air pressure, doesn’t it?

Certainly. But according to TMC data, it only takes about 20 minutes to check and adjust inflation pressure on an 18-wheeler. If you do it every week, chances are you’ll have very few problems with underinflated tyres. That means increased uptime, better fuel efficiency, longer tread life and improved retreadability – all of which can put real money into your pocket.

Bridgestone South Africa

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