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Calculating The Amount Of Fuel You Can Take On

Ok, so you've loaded up at the shipper, you've scaled the truck at a truckstop, and you're getting ready to fuel up. Now you may not be able to just fill it up or you could be overweight at the next weigh station. But you want to put in as much fuel as possible so you don't have to stop more often than necessary. So how can you determine how much fuel you can add?

Remember that a safe estimate would be to figure each gallon of fuel weighs 8 pounds. Here's an example for calculating the amount of fuel you can take on based on the weight of the steer axle (we'll get to the drive axles in a bit):

You get loaded at the shipper and you scale your truck at a truckstop. Your steer tires are rated at 6,150 pounds, all of the states you're travelling in allow 20,000 pounds on the steer axle, and your fuel gauge is almost on empty. Here's your weights:

• Steer:
  11,400
• Drives:
  33,100
• Trailer:
  33,700
• Gross:
  78,200

Assuming that 90% of the weight of fuel goes to your steer axle and 10% to your drive axles, how much fuel can you put in and still remain legal on your axle weights?

Well, your steer tires are each rated at 6,150 pounds which means you can only be 12,300 on your steer axle. You're currently 11,400 on your steer axle so that gives you 900 pounds you can add to your steer axle. The formula to deterimine how much fuel you can take on based on steer axle weight is:

So for this example, here's how you would solve this step by step:

First, here's the numbers you know for the formula:
900 pounds (amount of weight available for steer axle)
90 percent (percentage of fuel weight to steer axle)

Step by step:

900/90 = 10
10 x 100 = 1000
1000/8 = 125 gallons of fuel you can add

Naturally, you have to be aware of the fuel weight that will be added to your drive axles so you have to make sure you won't wind up overweight on your drive axles either (34,000 pounds maximum). All you have to do to figure out how much weight will go on your drive axles is subtract the amount of weight going onto your steer axle from the total weight of fuel being added. In this case you're adding 125 gallons of fuel. You multiply the number of gallons times 8 to get the total weight of fuel being added:

125 x 8 = 1000 pounds of total fuel weight added

Then you subtract the amount going onto the steer axle from the total weight of fuel being added:

1000 - 900 = 100 pounds of weight going onto the drive axles

In this case we only started with 33,100 pounds on our drive axles so we'll be at 33,200 after adding 125 gallons of fuel

Calculating Fuel For The Drive Axles

Most of the time when you're worried about how much fuel you can add, it will be your steer axle that will be the limiting factor because most of the weight of fuel is placed on the steer axle. But sometimes the drive axles can be overloaded by adding fuel. The formula for calculating how much fuel you can add based on the drive axle weights is exactly the same as the steer axle weights except you plug in the amount of weight available to the drive axles and the percentage of fuel weight that goes to the drive axles: