How to Calculate Vehicle Weight Distribution Grade

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Vehicle weight distribution is one of, if not the single most important aspect of, chassis design. It's the one factor that every other design parameter literally revolves around, and is simple to calculate. While front and rear weight distributions are the most widely published statistics, side-to-side distribution can play an equally crucial role in vehicle performance. This is especially true when you consider that a 200-pound driver represents about six percent of the vehicle's total weight -- and that weight sits on one side of the vehicle or the other.

Things You'll Need

  • Set of weights equal to your body weight
  • Take your vehicle to the local truck stop and ensure their scales inset into the ground instead of sitting upon a raised platform. This doesn't matter if you're only going for a front or rear distribution, but it does if you want a corner-weight calculation. Consider doing this late at night so you don't interrupt truck drivers who have somewhere to be.

  • Fill the tank with fuel. Place your weights on the driver-side floorboard as close to the seat as possible. These weights simulate your body weight while the attendant takes the measurement. Ensure you're not standing on the scales when they do the measurement.

  • Pull your vehicle onto the scales. Note the scales have three different plates, one for the front steer axle, a shorter one for the drive axles and a third for the trailer axles. Pull your vehicle up so that the front wheels sit on the front steer axle scale and the rears sit on the drive axle scale. Hit the button next to the scale and have the attendant take the weight reading.

  • Pull the vehicle up next to the fuel isle, go inside and get your weight ticket. Pull the car back around to the scales and repeat the procedure, but this time park it so that the right hand wheels are on the pavement and only the left are on the scales. The left front wheel should be on the steering axle plate and the left rear should be on the drive axle plate. Hit the button and say, "reweigh" into the microphone. Get your ticket and pay the attendant.

  • Note the front and rear weight measurements from the first and second weighs. Divide the front axle weight by the total vehicle weight to get the front axle percentage. Multiply by 100 to get the front axle's percentage and subtract from 100 to get the rear axle percentage.

  • Subtract the left-front wheel weight from the front axle weight to get the right-front wheel weight. Repeat for the rear. Once you have all of the wheel weights, divide the figures by the total vehicle weight and multiply the results by 100 to get a percentage for all four wheels.

Tips & Warnings

  • As an example, a Shelby GT500 has a total weight of 4,100 pounds, including driver and fuel load, with 2,330 pounds on the front axle and 1,700 on the rear. The weight over the left front comes to 1,351 and the left rear comes to 952 pounds. Divide 2,330 by 4,100 to come out with 0.568 (round to 0.57), and multiply that by 100 to end up with a 57 percent front axle weight. Subtract front axle percentage from 100 to get the rear axle percentage. As a result, this car has a front and rear weight distribution of 57 to 43. Next, subtract left-front weight of 1,352 pounds from front axle weight of 2,330 pounds to get the front-right wheel weight of 979 pounds. Subtract the left-rear weight of 952 pounds from the rear axle total of 1,700 pounds to get the right-rear wheel weight of 748 pounds. Divide all of your wheel weights by the total vehicle weight 4,100 pounds to get a total corner-weight measurement. This comes out to a left front percentage of 33 percent, a right front percentage of 24 percent, a left rear percentage of 23 percent and a right rear percentage of 18 percent. Note that these percentages may or may not add up to 100 (they add up to 98 in this example). This is a result of rounding off the percentages to the whole number.

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References

  • "Race Car Engineering & Mechanics"; Paul Van Valkenburgh; 2004
  • "Chassis Engineering"; Herb Adams; 1992
  • Photo Credit Rick Dole/Getty Images Sport/Getty Images
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