Hello. I have a 99 Ram 2500. Obviously Cummins. I only got about 14 MPG before my lift and 35 inch tires which I'm honestly a little surprised with. I typically only drive on the highway or straight back roads. I always got better MPG than average in any other vehicle I owned so I'm a bit surprised I'm getting worse than what everyone else seems to get. I get 13 now with the lift and tires. It's also a 5 speed. Any ideas to increase MPG or why it might be lower for some reason?

 

Welcome to DTR

Would like to know what your axle ratio is. I'm guessing 4.10's based on your mileage.

Lifts and larger tires will always impact mileage. How you drive it is also a factor too.


My truck is currently getting about 18-19 MPG, driving mostly on state highway and county roads. I can push that into the low 20's if I drive the interstate. But my truck has no lift, much smaller tires that what you have (285/75 R16), is a 2WD, and has a 3.55 axle ratio.

One last thought, check your fuel system for leaks. My truck had a drip from the fuel filter drain valve last year. When I replaced valve with a new one, my mileage went up by about 2 MPG. I was a bit surprised that the leak hit my mileage like that, and it was just a drip.

 

Also, how long have you been tracking the mileage? Up here in the cold climates, winter fuel can knock the heck out of your mileage figures, mine is about the same, 3.55 gears, 32" tires, and summer I can sneak 18-19, but winter it is lucky to break 15 MPG, and I drive like a grandpa.

 

On average these trucks will get anywhere around 18-20 mpg depending on driving style and terrain. Some get a little better, some get a little worse.....

The biggest variable being aerodynamics because physics shows us that it takes four times the HP to double the speed. Therefore any added wind resistance will cause the most reduction in fuel mileage.

So yes, any lifts which causes the trucks to sit higher in the air, and expose all the suspension components to oncoming wind, and wider more aggressive tires which will act like fans as they roll along.....will all cause reduced fuel mileage from the norm simply because they affect aerodynamics.

So people think rolling resistance from larger heavier tires is a cause of less fuel mpg, but really the side affects of such tires is minimal merely because of the truck travels less distance per rotation and the amount of HP it takes to keep the tires rolling is very little. Sure, a lot of larger diameter heavier tires wouldnt be an advantage in constant start/stop in town traffic. But again, aerodynamics is by far the biggest contributor to fuel mileage. For instance, I can tow an 8k flat bed trailer and get well over 15 mpg. But if I'm towing a 8k TT then I'm lucky to get 10-12 mpg.

There are some people who go through great lengths to keep their fuel mileage as high as possible too by messing with the IAT temps.
I've sent you a PM.....

 

Be sure you have calibrated the speedometer as your truck is rolling otherwise your mpg is not accurate.

What's said about aerodynamics is true. If you try to maintain around 60 mph +- a couple you will get optimum mpg. Going 70-80 pulling a trailer will sink mpg like the Bismark.

My son drives big rigs. They are governed to 64 max. They get a bonus for better mpg. He found dropping to 62 was worth a pretty good bonus of 1-2 mpg. It really counts up at 10-12k miles a month. He likes the trailers with the side skirts and aero wings on the back.

I've already posted my mpg but my 4 year total mpg is 20.5 for all driving. I drive like I might break the fuel pedal.