Posted by: Mark Polk | 2013

Gas vs. Diesel for Towing

Gas vs. Diesel

Gas vs. Diesel

There has always been controversy over gas vs. diesel, but what about when it comes to towing? Other than the cost factor, what are we really talking about when it comes down to gas versus diesel? This is where torque and horsepower come into the equation.

 Explaining torque and horsepower can get extremely technical, and I want to keep this simple and easy to understand. With that said, torque is basically the force or energy required to move something. Torque is the measurement of force, and force is measured in reference to a twisting or rotating shaft. In English terms torque is measured in pounds-feet, but it is more commonly referred to as foot-pounds. So in keeping it simple let’s just say that torque can be thought of as the amount of turning force it takes to move one pound of weight the distance of one foot.

 Torque can be multiplied through gear ratios. You have probably heard that a 3:73 axle gear set is better for towing than a 3:23 gear set. The axle ratio is the number of times the driveshaft must rotate to turn the rear wheels one revolution. If you have a 3.73:1 axle ratio the drive shaft turns 3.73 times for each full turn of the axle. So in a sense torque really equals towing capacity.

 Horsepower on the other hand is torque X RPMs. Torque is how much work is being done, and horsepower is how fast you get the actual work done. What’s interesting is, an engine rated at 350 horsepower only produces that horsepower at a rated peak power RPM. This RPM range, for a gasoline engine, is often between 5,000 and 6,000 RPMs. When an engine is idling the horsepower is rating is significantly lower, and as the RPMs increase so does the horsepower. When you are towing a trailer the engine speed is more likely to be in a lower RPM range, which means you probably have slightly more than half of the engines rated horsepower.

 Horsepower is measured by a dynamometer. A dynamometer puts a load on the engine and measures the amount of power the engine produces against the load at various speeds. In reality it is measuring torque in pound-feet and converting it to horsepower. Even at the rated peak power RPM you really won’t get the rated horsepower, because a percentage is lost through auxiliary equipment on the engine and the process of getting the power to the rear wheels.

In a diesel engine the horsepower peaks at a lower RPM, and there is more torque at a lower RPM compared to a gasoline engine. This results in a diesel engine having much more power at a lower RPM, around the RPM range you will be towing at. This higher torque and higher horsepower at a lower RPM equates to better towing.

 There are many other factors involved in the question of gas versus diesel that you will need to consider. What are the maintenance costs involved, cost difference between fuel types, fuel economy, your budget, and the resale value? But if the question is which truck will tow more the diesel wins hands down.

 Mark J. Polk

RV Education 101



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