Help with gas mileage!

[Trevor Myers]

Alright guys help me out,

 

In my 2017 silverado Lt I have recently put a 2.5" leveling kit, with 285/70 venom power terrains on a 17x8 moto metal wheel (stock is 265/65r18), resonated tip (for looks) and a k&n drop on filter. My best average was 19.9 and is now 15.4!? I was expecting a drop but not 5 mpg!

[14 Silvy]

You need to hand calculate it with the bigger tires your computer is showing you traveled less miles due to the larger tires. Also there will be a drop due to the size difference in tires and the rolling mass is increased and the contact patch is larger also.

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[Trevor Myers]

How do I calculate it? I know i have more rubber and friction and all that. But these tires are actually 3lbs lighter that BF ko2's and all the research ive done I've never heard of anyone losing that much. Also is 22 less rotations per mile alot?

[aseibel]

If you didn't recalibrate the speedo, your readings are going to be something like 3-4% too short.

 

So take the old tire's rev/mile and divide by the new one. That will tell you what ratio you need to multiply your mileage by to get accurate readings.

 

That's still not going to improve your mpg number by very much. Raising up the front end & adding wider tires kills your aerodynamics. 

[Trevor Myers]

So 639÷617=1.035 

15.4×1.035=15.9? 

[Donstar]

It takes very little to impact the mpg's on our trucks.  They achieve optimal efficiency when stock, unladen and driven gently.  Any changes to these factors and fuel consumption will increase.    Your mpg's, with the changes you've made, sound right based on what I'd expect.  I'm sure your truck looks good and I'd switch out of the mpg screen.  On my last truck I put on larger, heavier tires and took a significant hit at the gas pump.  I simply changed my driving behavior by eliminating an unnecessary trip or two during the week.  It sometimes costs to look good! 

[Eddie 70]

I went from factory 18's to factory 20's and lost 2 mpg. The weight difference was about 20lbs per wheel heavier. Factory wheels and tires.........

[Phil Murray]

12 hours ago, Trevor Myers said:

Alright guys help me out,

 

In my 2017 silverado Lt I have recently put a 2.5" leveling kit, with 285/70 venom power terrains on a 17x8 moto metal wheel (stock is 265/65r18), resonated tip (for looks) and a k&n drop on filter. My best average was 19.9 and is now 15.4!? I was expecting a drop but not 5 mpg!

⁸

[Phil Murray]

Part of the answer is -

What was your old worst and overall averages.  You want looks or you want fuel econ?

[amxguy1970]

13 hours ago, Trevor Myers said:

Alright guys help me out,

 

In my 2017 silverado Lt I have recently put a 2.5" leveling kit, with 285/70 venom power terrains on a 17x8 moto metal wheel (stock is 265/65r18), resonated tip (for looks) and a k&n drop on filter. My best average was 19.9 and is now 15.4!? I was expecting a drop but not 5 mpg!

Your new tires are approximately 1.1" taller so that is 3.5% larger which means you need to multiply your current mileage 1.035 (that is 3.5%). So your 15.4 mpg is really 15.9 mpg. As others have noted, your tires are heavier (stock were P-rated and your new tires appear to be LT rated), they are wider, taller and your truck is taller with the nose more up as opposed to having some aerodynamic rake. All that can certainly add up to nearly 4 mpg at highway speeds, that is a bunch going against the factory aerodynamics and weights. Did you also remove your air dam or do anything to it? Not much you can do but make sure the tires are inflated properly, make sure the air dam is on, maybe add a rear block to angle the nose down a hair for better aero (not lowering it) or lowering the truck a little, 2.5" is awfully larger and will add wear and tear on the front of your truck along with the heavier and larger tires. Gotta pay to play, I understood that when doing my truck so I added a 1.5" level, P-rated tires 1 inch larger but stock width and only trimmed the air dam instead of removing it, I lost between 1-1.5 mpg over stock. 

 

Tyler

[Grumpy Bear]

Biggest influence on mpg is your right foot

No one likes to hear that

But.....

[Bash74]

Some people say when they switch to winter blend gas the milage goes down. Are you on a winter blend now.

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[TXGREEK]

Alright guys help me out,
 
In my 2017 silverado Lt I have recently put a 2.5" leveling kit, with 285/70 venom power terrains on a 17x8 moto metal wheel (stock is 265/65r18), resonated tip (for looks) and a k&n drop on filter. My best average was 19.9 and is now 15.4!? I was expecting a drop but not 5 mpg!

Tires, it’s your tires. Add air, get a tuner (SuperChips), switch back to stock air filter and go from there.


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[aseibel]

31 minutes ago, Bash74 said:

Some people say when they switch to winter blend gas the milage goes down. Are you on a winter blend now.

The OP is from the other side of the state from me. We are definitely on winter blend now. I kind of ignore the fuel economy numbers from October to April and focus on the summer months, haha.

[Grumpy Bear]

2 hours ago, Bash74 said:

Some people say when they switch to winter blend gas the milage goes down. Are you on a winter blend now.

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Since September 15 we all have been. I post the following about twice a year at each change when this topic comes up: 

 

The difference between summer- and winter-blend gasoline involves the Reid Vapor Pressure (RVP) of the fuel. ... The US Environmental Protection Agency (EPA) says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better in the summer.

 

Winter gas accounts for a MAXIMUM of 1.7% of the mpg loss.