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Calculating Fuel Burnoff

At times you may find that you'll need to know how much fuel weight you're going to burn off in a certain distance. For instance, you're in Tennessee, which allows up to 20,000 pounds on the steer axle and you just scaled your truck. You're 11,800 on the steer axle and you have steer tires rated for 6,150 pounds, so you're legal up to 12,300 in Tennessee on the steer axle. You have 1/4 tank of fuel, you're 210 miles from the Arkansas line, and you're heading to Little Rock, Arkansas.

Tennessee allows 20,000 pounds on the steer axle, but Arkansas only allows 12,000. You already know that your truck puts 90% of the fuel weight on the steer axle. You'll need to know how much fuel you can add now and still be legal when you get to the Arkansas line.

When making any sort of fuel mileage calculations, you always want to be conservative. Most companies can tell you what fuel mileage you're getting, and in fact, most trucks have a readout right on the dash. Whatever your fuel mileage is, round it off to the most conservative number. Here, we don't want to overestimate how much fuel we'll burn off because we might wind up too heavy when we get to Arkansas. So if the dash says we're averaging 6.5 mpg, we'll round it up to 7 mpg for the calculation just to be safe.

To figure out how many gallons of fuel you'll burn off, simply divide the number of miles traveled by the miles per gallon:

Number of miles travelled / miles per gallon = gallons of fuel burned off

So we're 210 miles from the Arkansas line and at 7 mpg we're going to burn off approximately 30 gallons of fuel by the time we get to the state line (210 miles divided by 7 miles per gallon = 30 gallons of fuel)

30 gallons * 8 pounds per gallon = 240 pounds of total fuel burned off.

If 90% of the total fuel weight will come off the steer axle, we need to figure out how much weight will come off the steer axle if we burn 240 pounds of fuel.

Calculating The Weight Coming Off The Axles

For this example we know that 90% of the 240 pounds of fuel weight we'll burn will come off the steer axle. To calculate the percentage of a value, you simply multiply the total value times the percentage you're looking for, and then divide by 100. Here, we want to know what 90% of 240 pounds is so we plug in the numbers:

(90 x 240) / 100 = 216 pounds.

So if 216 pounds is coming off the steer axle between here and the state line, and we can be 12,000 pounds on the steer axle at the Arkansas line, then we can put in enough fuel right now to put us at 12,216 pounds on the steer axle. We're currently at 11,800 on the steer axle, so we have 416 pounds of weight available for the steer axle. From the previous page, we already know the formula to determine how much fuel you can take on is:

So we plug in the numbers:

  • 416 (amount of weight available for steer axle)
  • 90 (percentage of fuel weight to steer axle)
  • 416/90 = 4.62
  • 4.62 x 100 = 462
  • 4.62/8 = 57.7 gallons of fuel you can add right now and be legal at the Arkansas state line.

Multiple-Choice Questions:

Question #673 (1 of 4)

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Using the following numbers for your calculations, how much weight will come off your drive axles?

Miles per gallon: 6
Miles travelled: 360
Percentage of fuel weight on drive axles: 30%

  • 144 pounds
  • 300 pounds
  • 200 pounds
  • 210 pounds
To calculate the percentage of a value, you simply multiply the total value times the percentage you're looking for, and then divide by 100.
If you're getting 6 miles per gallon and you travel 360 miles:

360/6 = 60 gallons of fuel

60 gallons x 8 pounds per gallon = 480 pounds of total fuel burned off

Since 30% of the weight of fuel goes on our drive axles, we need to know what 30% of 480 is:

30 x 480 / 100 = 144 pounds coming off the drive axles
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Question #672 (2 of 4)

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Using the following numbers for your calculations, how much weight will come off your steer axle?

Miles per gallon: 7
Miles travelled: 280
Percenatage of fuel weight on steer axle: 80%

  • 280 pounds
  • 310 pounds
  • 300 pounds
  • 256 pounds
To calculate the percentage of a value, you simply multiply the total value times the percentage you're looking for, and then divide by 100.
If you're getting 7 miles per gallon and you travel 280 miles:

280/7 = 40 gallons of fuel

40 gallons x 8 pounds per gallon = 320 pounds of total fuel burned off

Since 80% of the weight of fuel goes on our steer axle, we need to know what 80% of 320 is:

80 x 320 / 100 = 256 pounds coming off the steer axle
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Question #671 (3 of 4)

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Using 6 miles per gallon as your fuel mileage and 8 pounds per gallon for the weight of fuel, how much total fuel weight will you burn off in 600 miles?

  • 850 pounds of fuel
  • 480 pounds of fuel
  • 800 pounds of fuel
  • 600 pounds of fuel
To figure out how many gallons of fuel you'll burn off, simply divide the number of miles travelled by the miles per gallon

Number of miles travelled / miles per gallon = gallons of fuel burned off
600 miles travelled / 6 miles per gallon = 100 gallons of fuel burned off

100 gallons x 8 pounds per gallon = 800 pounds of fuel burned off
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Question #670 (4 of 4)

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Using 7 miles per gallon as your fuel mileage and 8 pounds per gallon for the weight of fuel, how much total fuel weight will you burn off in 210 miles?

  • 210 pounds
  • 270 pounds
  • 240 pounds
  • 180 pounds
To figure out how many gallons of fuel you'll burn off, simply divide the number of miles travelled by the miles per gallon

Number of miles travelled / miles per gallon = gallons of fuel burned off
210 miles travelled / 7 miles per gallon = 30 gallons of fuel burned off

30 gallons x 8 pounds per gallon = 240 pounds of fuel burned off
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