Gas Mileage Drop

[Brandon Slaughter]

A few months ago I had a wreck where I ran off the road and hit a curb at around 60 mph in my 2016 Silverado 1500. All 4 wheels and tires, front bumper, front suspension, rear axle, some rear suspension, and a few miscellaneous parts had to be replaced. In the process I decided to upgrade wheels, tires and front bumper. The tires are only 33x12.5x20. I put a full Ranch Hand bumper/grille guard on the truck. Before the accident I averaged 20-22 mpg highway, and now I’m getting 12.5-13 mpg running the speed limit if I’m lucky. My question is, would the added weight of the bumper(around 200lbs) and the tires cause that big of a decrease in mpg? Or could there be something else possibly causing it? I put the same size tires on my 14 and still got 18-20 on the highway. Didn’t expect that big of a drop by doing the upgrades is why I’m curious. I’ll upload a picture so y’all understand what I’m working with. Thanks in advance for the help. 

[Grumpy Bear]

Wheels and tires are not just taller. They are heavier. OEM front bumper is part of the aero package which you no longer have. Yes the weight hurt. Wheel tire combo sits outside the body. Larger frontal area and again, spoils the drag coefficient . Your just tearing up the air and slinging more inertia. Tire type isn't fuel friendly either. Rolling resistance. Put a topper on it and you can probably get it down under 10 mpg. 

[swathdiver]

Let me add to Grumpy's post and suggest you get the truck up on an alignment rack, making sure the rear axle is tracking true and that the front wheels are set right also.  

[Doublebase]

Wonder if the added weight weight changed the alignment angles just a touch? You may have added a tiny bit more negative caster to the equation...steering might feel a little looser, might not return to center as easily/quick...but place a drag on the tires? Probably not unless it changed the camber setting...may have added a bit more negative camber to the equation, not sure on toe. And this is just when considering the additions to the front, not the accident you had. Because you have yourself a rather large drop in fuel economy...someone else mentioned rear axle tracking to the front. I agree. Also consider the time of year it is - it's colder - my fuel economy has dropped 3 mpg over the past three weeks, it's gotten cold. Cold = less fuel economy.     

[Grumpy Bear]

2 hours ago, Doublebase said:

 You may have added a tiny bit more negative caster to the equation...steering might feel a little looser, might not return to center as easily/quick...but place a drag on the tires? Probably not unless it changed the camber setting...may have added a bit more negative camber to the equation, not sure on toe.   

By 'a tiny bit more negative caster' I'm sure you mean 'less positive'. Right? 

 

Here's something not often considered. Changing wheel offsets changes turn in radius differential in turns. Akerman going straight and dynamic camber down the road. All this changes rolling drag. 

 

3 hours ago, swathdiver said:

Let me add to Grumpy's post and suggest you get the truck up on an alignment rack, making sure the rear axle is tracking true and that the front wheels are set right also.  

My rear axel was off a quarter inch from the factory! There was allot of work done to this truck and allot of fingers in the pie. Not hard to imagine someone was having a lazy day, eh?