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Tyre Tips - Light Commercial Vans, Trucks and Buses


Tyre Tip 2 - Truck Tyre Fuel Economy

We all know there's not much you get for free these days, but it would be nice in the case of your truck tyres that they could contribute to their own expense. I'm talking about being aware of what you can do to improve your truck's fuel economy performance via the tyres, and also what we see in the future in new tyre designs.

 

First, let's analyse where your fuel dollar goes in your operation. In an ideal steady state condition (i.e. on a straight, flat road), your engine power is required to overcome around 60 percent wind resistance, 12 percent transmission losses, and about 23 percent rollong resistance loss through the tyres. In a more realistic long distance application, losses have to accommodate hill climbing and acceleration functions, which add considerably to the fuel consumption. We estimate around 35 to 40 percent. Wind resistance in this type of service amounts to 30 to 35 percent, plus rolling and transmission losses add up to around 25 percent of the total.

 

If your truck was on general delivery operations, then the major fuel consumption is taken up in dealing with traffic and road conditions, with wind resistance and tyre roll resistance contributing little to the total fuel consumption picture. So the overall statement from this analysis is that tyres play a major role in fuel consumption in long distance applications, but a relatively minor role in urban or regional operations.

The next step in this tyre exercise is to consider where the greatest effect can be achieved. The simplest way to figure this out is to go with the greatest number of tyres. The two steer tyres only contribute about 10 to 15 percent to the overall rolling resistance; eight drive tyres contribute around 30 to 35 percent; and the greatest influence of all is through the twelve (typical) trailer tyres at around 50 to 60 percent. I'll leave it to you mathematicians to estimate trailer tyre influence on B - doubles and road trains!

 

What can you do to improve this situation? First, make sure your tyres are correctly inflated and regularly maintained. Anything less than the ideal pressure, which is matched to the load, will cost you money, not only in fuel but also in tyre life. As a rule of thumb, for each 5 psi down on the correct pressure you can lose around 5 percent in rolling resistance properties and also tread life. We are not asking you to over-inflate, since that brings it's own attendent problems such as uneven wear and impact resistance.

 

Second, review the tyre type and size you are using. We know that specialist shallow tread; ribbed trailer tyres can effectively reduce rolling resistance. This can be applied to recap selection as well. Similarly with traction drive tyres, the closed shoulder type tyres rather than the traditional cross rib have improved rolling properties. Lower profile tyres may not necessarily give you direct rolling property improvement, but the smaller packaging configuration may benefit you indirectly. Also, on the trailer, consideration should be given to the use of the wide base, super single tyre concept where six replace twelve standard tyres. This can improve your roll characteristic by up to 15 percent, as well as reduce weight contribution by about 20 percent.

 

These figures sound promising, but it should be understood that rolling resistance figures are on a ratio of around seven to one for fuel consumption. Therefore if you improve the overall rolling resistance of your rig by 21 percent, this will amount to approximately 3 percent fuel savings. This may not sound much until you translate it into, say, a 3 percent saving on your yearly fuel bill. An average interstate truck covering 280,000 kilometers a year can go through a serious amount of fuel and money. We estimate a cost saving of around $4000 could be achieved on the above figures --- which would go a fair way towards your next set of tyres!

 

All this goes out the window, of course, if the wrong type of driver is in control of the truck!

Another aspect is that a 3 percent improvement is hard to measure unless accurate monitoring figures are kept to identify the change. I personally believe this is a major reason why there has not been more impetus locally to push towards fuel-efficient tyres. Fleets have been more interested in obtaining treadwear results rather than economy they cannot measure easily.

 

Responsible tyre manufacturers now have their versions of fuel-efficient tyres available internationally and reflect their various approaches to improving the inherent rolling resistance of the radial truck tyre. It is inevitable that this concept will become popular here as fuel costs and environmental legislation escalate while competitive margins decrease. . We can perhaps revisit this subject in the future, and investigate just how these design changes in a tyre can improve their rolling qualities.