For many people tyres are just those black things on a vehicle which I have to check when they look flat or the car lets me know. My fingers get dirty – it’s a task that sucks. The only other time I hear about them is when the car is getting serviced and I am informed I need new tyres.
Uggh – suddenly this trip to the mechanic is costing me more. Sadly, this is how many road users view their tyres. Is this a fair assumption or are we being ignorant??
To give some insights NRSPP chats with tyre expert, Adam Gosling, of TyreSafe Australia on the basics of tyres.
When a tyre is rolling down the road it consumes energy. On a vehicle this energy is provided by the fuel. The degree of resistance to rolling is caused by many factors, the design of the tread pattern, the casing of structural members of the tyre, the road surface itself and the largest factor of them all is the inflation pressure of the tyre.
Remember getting your push bike home when it had a flat tyre? It was a lot of work wasn’t it? The road surface hadn’t changed only the inflation pressure of the tyre.
When a tyre supports a load on a vehicle it deforms under load. There is a technical term known as
hysteresis, this explains the way a block of rubber is deformed and the energy it consumes. The higher the load the higher the deformation, that’s simple. With an increase in vehicle speed comes an increase in the frequency of the deformation but there is a catch. The faster the vehicle travels the greater the deformation caused by the load. A small bump in the road at slow speed can be a large bump at high speed. So, the energy consumption due to hysteresis is exponential. A technical way of saying the faster we go the more energy we consume; a lot more than we would be travelling slowly.
A tyre moving about the suburbs travelling slowly, not carrying a lot of load barely increases in pressure. The same vehicle travelling at highway speed shows, with properly inflated tyres, we observe an increase of up to 15% over the cold setting. Put some load into the vehicle and suddenly the tyres are over working, the operating pressures are heading north of 15% indicating the tyre is over working.
A tyre supports the load imposed on it with the air contained inside. The higher the load the more air required. Remember the hysteresis? The faster the vehicle travels equals the more air the tyre requires. So, when you’re driving around the city with a light load your tyres aren’t working. As soon as you add more load and start going faster your tyres require more air to support the load and the speed.
When a tyre is formed it is a one-way process that combines chemicals and raw rubber to form what we know as a tyre. It’s not like freezing water where when it defrosts it turns to water again. Making a tyre is like baking a cake, when it’s made that’s it. It can’t be unmade!
When a tyre reacts to work when be used on the road it generates heat. It generates a lot more heat than just sitting in the sun, you can’t tell how hot a tyre is by feeling it generally. The heat is inside the tyre structure. By the time you can smell it and think “wow that tyre is hot” the damage is done, the cake is burnt. By this time the inflation pressure will have increased probably well beyond 25% above the cold pressure, far too much.
Tyre manufacturers suggest that for road use pressures should be in the 10% ‐ 15% range. Any
higher than that the tyre is over working. In specialist tyres like motorsport and the giant haul truck tyres the pressures do go higher but those tyres are working a lot harder than normal road tyres.
I prefer to set mine at 19% above cold, yes there are times when I work the tyres hard, I carry a big load and I know this is worth 2 – 3 psi on the run home. IF you have monitoring technology installed and get an alert that the tyres are in danger of overheating, the easiest way to cool the tyres is to slow down, remember that exponential increase? It works the same in reverse too, just 10 km/hr will make a lot of difference to the work a tyre does at highway speed.
Under pressure is where damage is done quickly. If I ask you to carry a heavy load you can walk well
enough, but if I ask you to start running then you will perish quickly, a tyre is no different.
So why is this important?
By not understanding how tyres are performing users use a lot more fuel (remember pushing the bike home?) and wearing tyres out a lot faster, there’s a double loss which compounds. The result is tyres are changed more often, can’t sell the casing or use them for retreading but worst of all is
endangering cargo and other road users.
If a tyre is underinflated and it fails catastrophically, (yes like the road gators you see on the roadside) then there is a potential loss of control.
Tyres may be just those dirty black things on a vehicle for most road users, but they make the world of difference in operating efficiently and safely. Plus think about how you can also reduce your environmental impacts with some simple tyre habits.
What are your tyre habits and how does your organisation approach managing their tyre risk?
A few good habits to get into are:
- Check your tyres weekly
- Consider your load and pressure as part of a journey plan
- Check you have a working spare before long trips
- Consider whether a tyre pressure monitoring systems will make life easy
- Purchase reputable brands, they cost more up front but save in the long term.
For more information visit the Tyre Safe Australia website.