| Speed | | | The speed that is used will affect the fuel economy. Constant speed, controlled electronically will ensure that any changes in truck configuration will be notable. That’s why we did some tests on a special test track, and some on a straight highway, but all with trucks that were limited to a maximum speed.
Since Airtabs™ reduce drag, one of the possible benefits is that for the same amount of horsepower, the truck can go faster. The problem is that if you go faster, you won’t see any improvement in fuel economy, just an improvement in time. Unless your trucks are governed to run at a constant speed, look carefully at the tachometer logs to make sure the speeds are the same! | | | |
| | | | What We Did | | | The first place the Airtabs™ were tested was in long distance runs with a fleet in the USA. For this test, the tractors only were fitted with Airtabs™ . This 3 month trial was long enough to remove any minor variations, and showed a consistent 3% fuel savings.
The next test was done in England at a test track, where two heavily loaded trucks were fitted with a partial set of Airtabs™ (less than half the normal kit) only on the tractor. The tests were extremely accurate - to give you some idea of how accurate, the fuel temperature was measured as well as the volume and weight. The average speed for these tests was only 47 mph, but even with a partial fit and this slow speed, an average of 2% fuel was saved when Airtabs™ were fitted. A full set of Airtabs™ only on the tractor at 60 mph average speed would save at least 3%.
The most recent set of tests were done on a company running consistent loads between two points that are some 250 miles apart. Airtabs™ were fitted to the tractor and the back of the trailer. The same drivers are used all the time, and the company has been keeping very accurate records for many years | | | |
| | | | Tire Pressure | | | | The wrong tire pressure will affect the fuel consumption. (For the test track, the tire pressures weren’t changed between runs, and for the over-the-road tests, the results were averaged over several weeks) | | | |
| | | | Drafting | | | | Running close behind another truck can improve the fuel economy of the rear truck, and make the fuel economy of the lead truck worse. On the test track, the trucks stayed at least 500 yards apart, and for the over the road tests, the drivers did not draft at any time. | | | |
| | | | Traffic | | | | Stop and go traffic or lots of speed changes will affect fuel economy. Obviously, there should be no other traffic on the test track!, . | | | |
| | | | Drivers | | | | Perhaps the largest difference that can be found in fuel economy tests is the driver. Late braking, or heavy acceleration will waste fuel. (For the test track, the drivers were kept the same, their runs were monitored to be the same to the nearest second, and for the over-the-road tests, the same drivers were driving the same trucks before and after Airtabs™ were fitted) | | | |
| | | | Load | | | | Different loads take different amounts of power to move. Heavier loads will mean more rolling resistance, and poorer fuel economy. (That’s why the same loads were used on the trucks on the test track, and for the over the road tests, we knew the trailers were carrying the same loads on all the runs.) | | | |
| | | | Rain or water on the road | | | | Water standing on the road affects fuel economy. If you think of the effort necessary to pump that water out from under your truck’s wheels, that energy has to come from somewhere- and that somewhere is your engine. A truck rolling down the highway can pump as much as a ton of water per hour, and that can affect fuel economy by up to 6%.(that’s why we did the tests on a dry test track, and for the over the road tests, compared long-term results for several months) | | | |
| | | | Wind | | | At 60 mph (100 km per hour), wind resistance is about half the total drag on the truck. At 70 mph, it’s two thirds of the total drag. The rolling resistance doesn't change much with road speed, but the wind resistance changes dramatically.
So if you’re doing 60 mph road speed into a 20 knot headwind, then you've got 80 mph of wind resistance. Turn around and make the wind a tailwind, and you are driving into a 40 mph of wind resistance. | | | |
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