We know you’ve heard this time and again, slow down to get better fuel mileage, but it’s not that simple. Getting the best fuel mileage means finding the sweet spot – the best RPM to run your engine so it’s the most efficient. And with fuel costs consistently ranking as driver’s number one expense, the best way to save money on fuel costs is to find the sweet spot where your engine runs.

The trick is pulling your load with torque and not horsepower, and using the energy in the right way. When you pull with horsepower you use more energy, and therefore burn more fuel to pull your load.

Torque helps sustain speed when towing or maxing out your vehicle’s cargo capacity—especially in maintaining speed going up hills. If you know there’s a hill ahead, gain speed before you climb it. It will prevent you from shifting gears to get up the hill, using more horsepower.

One way is to think of it as if you’re riding a bike.  If you see a hill, you’re going to start pedaling faster – you have to get the momentum going to get up the other side easily.  If you were to pedal at the same speed, you would have to work much harder to get up and over the hill.  It’s the same thing in your truck.  Why work harder and waste the energy if you don’t have to?

Your dealer states peak horsepower and peak torque at specific RPM for each engine. Even though the RPM varies, we consistently found somewhere between 1250 - 1350 RPM is the magic number. The number not to exceed is 1500 RPM. You can contact your dealer to find the specifics for your engine and where your engine’s sweet spot is.

We aren’t telling you how fast you should drive, but if you want to save on fuel - finding that sweet spot can leave a sweet amount of savings in your checking account.

Click here for the Team Run Smart Webinar on Driving for Fuel Efficiency!

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Comment ()


Lane Scott,

Which rear end ratio do you have? Do you have a lot of chrome or accessories on the exterior? Are you running in crosswind or up steep hills under loads? What temperature are you running in typically? (in the summer I expect a slight drop caused by loads from the air conditioner, and you posted in what is the last part of summer).

How are you determining your mileage? If you're just relying on the sentinel it might be 0.5 to 1 MPG off so track your mileage on paper or using an app such as Fuel Gauges by Kevin Rutherford (http://www.letstruck.com).

The truck only runs 1100 RPM in 10th at 55 MPH, or roughly 1250 at 62 the way my company configured it. In 9th, the sweet spot is roughly 52 MPH or roughly 1350 RPM. I get 6 MPG under heavy loads in zero degree temperatures and roughly 7s in temperatures of 30 to 50 degrees. The warmer the temperature, the better the fuel mileage should get up until the outside temperature gets to roughly 75 degrees, at which point air conditioning loads might cause a drop.

Time and HOS are often factors when I run. Weather is also a HUGE factor. It's too bad some companies dictate routing to destinations because sometimes going south or routing around a storm IS the best option to help the fuel mileage.

In the winter, Illinois sometimes gets winds up to 70 MPH along with the snow and ice. Routing decisions not only affect fuel mileage but can also mean life or death in the winter and early spring in Illinois. I'm sure other states sometimes get similar conditions, especially in mountainous or wide open areas.

Be safe, and try seeing what your fuel, oil and DEF consumption are on paper. I'm sure you might find the answer soon.

January 04, 2015 17:19:06 PM

Lane Scott,

Which rear end ratio do you have? Do you have a lot of chrome or accessories on the exterior? Are you running in crosswind or up steep hills under loads? What temperature are you running in typically? (in the summer I expect a slight drop caused by loads from the air conditioner, and you posted in what is the last part of summer).

How are you determining your mileage? If you're just relying on the sentinel it might be 0.5 to 1 MPG off so track your mileage on paper or using an app such as Fuel Gauges by Kevin Rutherford (http://www.letstruck.com).

The truck only runs 1100 RPM in 10th at 55 MPH, or roughly 1250 at 62 the way my company configured it. In 9th, the sweet spot is roughly 52 MPH or roughly 1350 RPM. I get 6 MPG under heavy loads in zero degree temperatures and roughly 7s in temperatures of 30 to 50 degrees. The warmer the temperature, the better the fuel mileage should get up until the outside temperature gets to roughly 75 degrees, at which point air conditioning loads might cause a drop.

January 04, 2015 17:10:48 PM

I HAVE A 2005 KENWORTH T-600 WITH A C-15 466 HP CAT ENGINE IM LIKE JEFF CLARK WITH E LOG TIME CAN BE OF THE ESSENCE. BUT FOR THE MOST PART 1350-TO 1400 IS MY SWEET SPOT.

December 24, 2014 6:18:43 AM

DD 15 Detroit 18sped 373 22.5 love the truck was getting 6.8/6.9 in the summer mths now we are in the winter fuel I'm down 5.8/5.9 thinking on putting a wing on the roof???

November 19, 2014 16:16:12 PM

Lane--- There are a number of things that may be causing this problem. How does the truck perform otherwise? Some things to consider would be:axle misalignment, is the truck driving straight and true? Any excessive or irregular tire wear? Does the truck seem to be lacking in power going up an incline? If so you may have a turbo boost leak. You might consider having the Charge Air Cooler and associated hoses and piping checked for leaks.

September 02, 2014 12:18:27 PM

I have a 2010 cascadia, ten speed transmission. I have found it does not matter what speed I drive ,I can only get high fives to low sixes. suggestions welcome,please help

September 01, 2014 13:41:22 PM

Ross ---- which DD engine do you have?

August 25, 2014 12:40:57 PM

This is the first DD I have own so tying to fine her sweet spot but the HOS are factors and at times have to hammer down !!!! How about me hauling van with a mid roof????

August 16, 2014 18:49:20 PM

Great article! Thanks for including a link to the webinar!

July 29, 2014 13:38:36 PM

Great information Bill!

July 28, 2014 9:41:27 AM

Like Jeff, I do the same, unfortunately like he said below, Time and HOS does interfere with ideal operating conditions.

July 24, 2014 14:31:18 PM

I have a 2006 Columbia with a 470hp 12.7 DD and an Eaton- Fuller 10 over. I find that my sweet spot is actually 1400-1500 range. The engine doesn't like below 1300 in high range and in tenth gear 60 is the slowest I can go. Running through the mountains with a ten speed isn't fun, but if I hit the uphill at 68 I'm in that sweet spot range and it will pull. I know that you prefer to be closer to the 62-65 mph area, but I have found that this truck will actually accelerate up hill from 70. I think part of that is the gearing, the speedometer is off by 5 mph so I'm pretty sure the previous owner changed the ratio.

July 23, 2014 20:14:11 PM

I run mine in the 1350-1375 rpm range. Time and HOS can be factors, there are times when I will knock it up to the speed limit.

July 21, 2014 6:47:10 AM

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About Bill McClusky

I have been in the trucking and construction equipment service industry for 23 years as a service technician, component rebuild specialist (engine, transmission, and axle), service department manager, instructor and consultant. I was a class 8 truck driver for 3 years pulling wet and dry tanks. I have been with American Truck Business Services for 4 years serving as a Business Consultant, Maintenance Consultant, and Instructor.

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