I know everyone says that Dodge and Chevy are getting better mileage than the new 6.4 and has more power. Just keep in mind that ford is the only one that offers 20" wheels and that makes a huge difference mileage wise and power wise. I know that when i just put a little wider tire on my truck that the mileage went down 1 mpg. I think that if the competition offered 20's, they would see 12-14 mpg also. So when someone comes in and says that their dodge and chevy and burn the tires through 2nd gear, just remember they have pizza cutters on them.

 

I would tend to disagree with it effecting it 2-4mpg. The rolling diameter difference between the two tires is only 1" (33" for 18" rims vz 34" for 2"rims) and the width is the exact same. But the weight is close to the same since the FX4 18" rims are chrome clad steel and the 20" rims are aluminum. Now, once you step up and change tire sizes to aftermarket, I would agree that the mpg would be effected. MPG is more effected my driving style than tire size.

 

I Would Dissagree.. If You Have A Slightly Larger Tire It Means You Are Turning A Lower Rpm Wich Means Better Fuel Mileage. With Gas Engines There Is A Difference Because They Dont Produce The Tourque That Diesels Do ....just Remember When Its All About Fuel Mileage . Lower Rpm Means More Mpg When Diesels Are Concerned

 

That depends. If the great majority of your diriving is at speed on the highway you might be correct. But every time you accelerate the increased rotational inertia of the larger diameter wheels and tires will have an effect. Especially when you consider the largest OEM tire on a Chevy is a 265/70 on a 17" rim, weight of 49 lbs and diameter of 31.7". The smallest tire on a Ford is 275/70 on a 18" rim, weight of 57 lbs and diameter of 33.4". Then the 20" are 275/65, weight of 60 lbs and diameter of 34.1". I have no doubt that this affects the mileage on these trucks as well as the additional weight of the truck itself. The choice for the consumer then comes down to, do you need a heavier duty truck or do you want to save a little in fuel economy.