Bad MPG?

JimCost2014 · August 28, 2021

4 minutes ago, MikeBMW said:

Well, you do you, but leave politics out of this forum, please.
I come here to get away from all that.
I want to know about our trucks and issues, mods, trouble shooting and all that.
Hey, that's just me, I guess.

Sorry, page 5

Lambo’s 2021 GMC Sierra 1500 AT4 Build

MikeBMW · August 28, 2021

5 minutes ago, JimCost2014 said:

Sorry, page 5

Lambo’s 2021 GMC Sierra 1500 AT4 Build

Link?
Maybe we can both stop running this thread off the rails?

Edited August 28, 2021 by MikeBMW

JimCost2014 · August 28, 2021

11 minutes ago, MikeBMW said:

Link?
Maybe we can both stop running this thread off the rails?

JimCost2014 · August 28, 2021

11 minutes ago, MikeBMW said:

Link?
Maybe we can both stop running this thread off the rails?

Grumpy Bear · August 28, 2021

12 hours ago, MikeBMW said:

I *might* have a bit of a lead foot (don't want to lose my drive safe and save State Farm insurance discount) but all of my driving (95%, anyway) is city driving - stop signs, waiting at stop lights often, etc).
I don't really care since my office is only two miles from my house.
I haven't really tracked the few highway miles I've driven but I do design work at some farms in the area that require a bit of highway miles as well as getting out of town and, combined, I can, sometimes, get to 15-17 MPG.
I've yet to try a full highway MPG test, though.

Poor truck.

:nonod:

You need a unicycle.

Grumpy Bear · August 28, 2021

12 hours ago, CarsonF said:

I’ve always used shell 87. 55,000 on the truck. Yes it’s been decreasing since the lift was installed. My buddy has a 2015 with the same set up and he easily gets 17-18 mpg. Just wondering why mine was so much lower.

Let him drive you truck. Seriously. If it improves....then.....well......you drive like MikeBMW :rolleyes:

mikeyk101 · August 29, 2021

On 8/27/2021 at 1:03 PM, rav3 said:

Tire diameters are larger, which results in lower RPM's, wouldn't that lower miles that you gas mileage is calculated from. Just a guess on my part. Don't they need to change something that runs the speedo to correct for that? Just a wild guess on my part.

Youre on the right track. Because larger tires are on, the speedometer would need to be corrected in order to display your true speed. What you may not have noticed is that your speedometer will read a bit slower than the speed you are actually traveling. You can verify this by using the speed function on a portable GPS or something like Google Maps on your phone. So now you have to realize that you are traveling the same distances as before, using the same amount of gas, but your speedometer and odometer will be reading less miles traveled. Hence, you will see a reduction on your mpg. I would bet that you are still getting the same mpg as before, you are just using methods that are now in error. You either have to get your speedometer recalibrated or start using another method such as miles traveled as reported by a portable GPS to calculate your actual mpg.

Ravenkeeper · September 17, 2021

I'm running 285/65R18s on mine, stock. I drive conservatively (for the most part), use the cruise (RELIGIOUSLY, set at the speed limit, absolute MAX speed of 65), I even use my cruise to slow down or speed up as needed, don't hard brake, don't jackrabbit take-off, and avoid long excessive idling situations. Added a tonneau cover a few months back, barely improved my MPGs.

Z45 · September 17, 2021

Oversize tires are usually much heavier than the tires that come stock, the extra weight and height of the tire will affect performance. The taller the tire, the higher the gear ratio (lower number) will become. Larger tires will also have a larger rotating mass due to the increase in weight. Both of these issues will result in a loss of low end torque. Your engine will have to strain harder to get the wheels rolling at the start. The smaller the engine, the more it will affect performance and put a strain on all components not to mention up-sizing, or installing a taller tire, will lead to a speedometer reading that is slower than your actual speed. This is because a taller tire will have a larger overall circumference, which will cause it to travel more distance per revolution than the original equipment tire.

MikeBMW · September 19, 2021

On 9/17/2021 at 5:53 AM, elcamino said:

This is because a taller tire will have a larger overall circumference, which will cause it to travel more distance per revolution than the original equipment tire.

Yep. I did a tune with the Flashpaq F5 for 91 octane performance and set my 35s to 34.5 (actual diameter) in the ECU and my mileage went from 10.3 to 11.7 so far. Mostly city driving, a few trips of 20 miles or so.
Setting the tire size to actual size does make a more accurate reading via the truck computer.

Edited September 19, 2021 by MikeBMW

swathdiver · September 19, 2021

On 8/27/2021 at 8:51 PM, CarsonF said:

I’ve always used shell 87.

I can always count on Shell to drop my mpgs by at least 2 mpg, even when burning 93. Speaking of 93, you ought to treat your motor to some and she how she then responds hauling all that weight around.

You can measure performance in mpgs but might consider also CPMs or Cents Per Mile.

Each tire on our 6.2 Sierra weighs 81 pounds, the truck will get about 10 mpgs in the city. 11 with a mix and 13-14 on the highway on 93 octane gasoline. She gets 8.5 mpg on ethanol in the city.