2014 GMC All Terrain 1500 5.3l 4WD FUEL ECONOMY

[bcarlton0158]

Ok, so I bought my 2014 1500 GMC All Terrain in September. My first
trip to New Orleans the disp showed 20.8mpg at 70mph. Best was
22.2mpg. After this trip I had the recall performed to replace the
throttle body and there was another recall to reflash the computer.

 

I also leveled the front end and swaped out the stock tires 20" Tires for some Toyo All Terrain 275/60-20s.

 

The
tires are around 2" taller so I know this affected the computer
calculations, but how much should I expect this to change my fuel
economy?

 

Truck is near 6,000miles now and shows
16.5-17.0 mpg for the same trip to New Orleans. Obviously around town
is worse, maybe 15.

 

My wifes 2012 Yukon Denali gets 14.5-15mpg around town and 17 on trips. Thats with a 6.2 l and a heavier vehicle.

 

Thoughts?

[bladz1454]

I think between the tires and possible winter blend, it doesnt seem too crazy. Do they use winter blend down there? If not, then yea that is very strange.

[fondupot]

Actually 275/60r20's are only about 1" taller than the stock tires (275/55r20). So your speedo is off by 3.4% (slow). So that means when your speedo says 60 mph, your actually going closer to 62 mph. This causes whatever your odometer to read, read low by about 3.4%.

 

So lets say your trip odometer reads 360 miles. Add in another 3.4% which is about 12.24 miles. So the trip should actually be 372.24 miles. With the same amount of gas used compared to each trip calculation you'll get the difference in mileage.

 

340 to 20 gallons of gas = 18 mpg

372.24 to 20 gallons of gas = 18.612 mpg.

 

However this calculation does not include loss of mileage due to heavier mass and more friction due to aggresive treads of the new tires. So once you figure that into the equation, you can see how it really would lower the mileage significantly. I dont think the 16.5-17 mph is really all that low considering the circumstances.

 

get your speedo recalibrated and things should even out, but don't expect to get the stock mileage with the bigger tires even if you do.

[bogeypro]

that fondupot fella is good with a calculator.... LOL

[Joe_K]

Fondupont is spot on. You also leveled the truck which hurts highway mileage as well.

[TJay74]

Main reason I went with lowering the rear to level mine so to keep the truck out of the airflow.

[fondupot]

Main reason I went with lowering the rear to level mine so to keep the truck out of the airflow.

 

Just curious did it help your mileage?

 

 

Sent from my iPad using Tapatalk

[TJay74]

Oh heck I don't know for sure, it was done right after I bought the truck. Putting the truck lower to the ground is always going to be better than putting it up further in the airflow.

[bogeypro]

I have thought about doing the same thing - lowering the rear. My last one was lifted, but lets be honest.... I don't go offroad unless i have to jump the curb at Chick-fil-a so I don't need the lift.

[bcarlton0158]

Thanks for the information guys. I am in Alabama and as far as I know, they do not use winter blend here.

 

The tires I bought are not very aggressive and are no wider than the stock tire. They shouldn't have added a considerable amount of I sprung weight, IMO. Not sure of the exact weights.

 

I agree the leveling would affect the fuel economy, but 4-5 mpg?

 

Perhaps it is just the combo of issues as you all mentioned?

 

I spoke w the sales manager here at the dealership. He has the same truck w 6" lift and aftermarket wheels and tires. 35" mud terrain.

 

He is getting 14.5-15mpg which is better than what my truck is getting.

 

What options do I have to re calibrate the speed odometer? The dealership claims they cannot and said an aftermarket programmer would void the warranty.. Ideas?

 

Thanks again for all of your feed back.

[TJay74]

Only option to re-calibrate speedo is to go back with stock size tires, get the hypertech re-calibrater, or use something like HP Tuners to do it. While the dealer is correct you will be tuning the ecm, it would not "void" the warranty if that was all you did. Now if you get into changing parameters in the engine and or transmission it will be a whole 'nother story.

[bcarlton0158]

Thanks Jay

[DanielAcosta]

I've been very happy with the Hypertech speedometer calibrator. It definitely allows the engine to shift up sooner and spend more time in V4. Under light acceleration I can actually accelerate from 15-50mph on 4 cylinders. Yes, I am still getting less mileage than stock, but 18 in town, 22 highway, 20 overall after 12,500 miles with a small lift and 34 inch tires seems pretty reasonable to me.

[steig]

 

I've been very happy with the Hypertech speedometer calibrator. It definitely allows the engine to shift up sooner and spend more time in V4. Under light acceleration I can actually accelerate from 15-50mph on 4 cylinders. Yes, I am still getting less mileage than stock, but 18 in town, 22 highway, 20 overall after 12,500 miles with a small lift and 34 inch tires seems pretty reasonable to me.

 

I've been very happy with the Hypertech speedometer calibrator. It definitely allows the engine to shift up sooner and spend more time in V4. Under light acceleration I can actually accelerate from 15-50mph on 4 cylinders. Yes, I am still getting less mileage than

stock, but 18 in town, 22 highway, 20 overall after 12,500 miles with a small lift and 34 inch tires seems pretty reasonable to me.

That's very good mileage.

[Aaron1085]

I have the 5.3 with 3:42 gears and 20" wheels......

 

I'm only at 875miles and averaging 14.6mpg here in New England. Ran a tank of 87 and a tank of 93 octane. I drive a lot more conservative in this thing compared to my Old car, but still cruise at 80-83 on highway. Anticipating mpg may increase a bit when more miles are put on the truck?

 

I haven't even really "pinned" it yet, want to treat her right as she is my first NEW vehicle.