We know there are a lot of diesel junkies out there who are into math and physics, so we decided to put a few basic calculations in one place so everybody out there in reader land could have them handy. Math can teach us a lot about our diesel trucks-everything from projected horsepower, to how gear ratio changes can affect your cruising speed.
Cargo Capacity
This is a basic calculation for how much junk you can cram into your truck's bed. To calculate cargo capacity, just multiply the truck bed's inside length, by its width, by its height, and there you go. Knowing cargo capacity can be useful in answering questions such as "Can I haul a cord (4x4x8) of wood?" Having this calculation will tell you how many trips you'd need in order to haul the full load.
Gross Vehicle Weight Rating (GVWR)
Speaking of cargo space, you also have to make sure you're not overloaded. All diesel trucks have a Gross Vehicle Weight Rating that lets you know how much weight you can carry before your truck becomes overtaxed. Because you can put so much more weight in the bed (because the engine is up front), front and rear weights are often very different. To use Feature Editor Mike McGlothlin's '97 F-350 as an example, his vehicle's GVWR is 9,200 pounds, but his Gross Axle Weight Ratings (GAWRs) are 4,600 pounds front, and 6,084 pounds rear, respectively. Notice that you can't simply add the front and rear GAWRs and get the GVWR, rather the front and rear numbers are the maximum amount of weight you can load over the front and rear axles as long as the total truck weight does not exceed 9,200 pounds.
Miles Per Gallon
This one might be simple. Calculating miles per gallon is as easy as miles traveled divided by gallons used, right? Well yes, but you have to be pretty accurate. If you drive a short distance, or the pump automatically stops at a different point, you can be as much as 2-3 mpg off. Drive a long distance when calculating fuel economy, and fill up as carefully as possible.
 Weight is a big factor in...  Weight is a big factor in a vehicle's performance. Look for more engine swaps in the near future, as lighter weight means better performance, handling, and fuel economy. This Duramax-powered Grand National clone gets more than 30 mpg while making more than 500 horsepower. |  This one isn't a diesel, but...  This one isn't a diesel, but this shows you what happens if you leave off the "height" in your cargo space calculation. We're also pretty sure this vehicle is over its GVWR. Believe it or not, we've actually seen this rig move a few blocks under its own power. |  If you have a little fuel-saver...  If you have a little fuel-saver diesel, your calculations have to be very precise. In a car such as this '82 diesel Chevette, a half-gallon miscalculation can throw your result off by 5 mpg or more. |