Of course there are many contributing factors when it come to gas mileage. Overall more people are getting 15-17 on the highway than not. If your engine is not broke in it will not reach that high. If you idle for 10 minute to get it warm and then only drive 10 miles it won't. If you pull 10K it won't. If you carry 3K worth of tools and tool boxes it won't. If you have your hubs locked in 24-7 it probably won't. If your drive has more redlights than miles of road it won't.. If you drive like John Force you won't.

 

Factory 20's are ever so slightly more than 34" tall. The typical 18's are less than 1" shorter than that. The 17's are shorter, yes. Tire size does play a role in fuel economy, but in interesting ways. The taller the tire, the lower the engine RPM at highway speeds, maybe equals better economy than with a shorter tire. However, the truck also works harder in the lower gears to get everything moving up to speed - the speeds at which the transmission changes gears is different. This usually equates to slightly lower economy in stop and go situations. You also have to factor in the heavier weight of the tire and rims vs the smaller wheels. The extra weight also slightly lowers economy, and adds more unsprung weight, reducing ride quality. Likewise, a smaller tire will allow the transmission to shift into the higher gears sooner, but will rev a little higher on the highway, possibly slightly lowering economy. Larger tires also slow acceleration.

As for fuel economy overall, I don't think most people are getting 15-17mpg. I keep my hubs locked in all the time during winter, and I lose 0.5-1mpg for this luxury. People should be very specific - is the fuel economy you are talking about something you saw once, or every time? Warm weather or bitterly cold? Do you live in hilly areas? Etc.

 

12-14 mixed, unloaded.

7-10 mixed with TT hooked up.

My first trip out with our TT I used tow/haul the whole time and just let the truck do it’s thing. On the way to the camp ground, about 250 miles, it was hunting for gears and never went into 6th gear (7-8 mpg). On the way home it was smooth as silk and holding 6th gear at 55-60 for long stretches (9-10 mpg). The adaptive learning on this truck is amazing. I like how you can up-shift or down-shift just by using the gas pedal when in tow/haul. For what it’s worth, I reset my milage meter with every fresh tank of gas.

 

I completely agree.

When we don't qualify our mileage reports it can be misleading. As for me, I usually only get 11-12 with mixed 70city/30Hwy per tank full. The area where I live is mostly flat with small hills and very little wind. My last tank was at 15.8 as I drove over 300 miles on the Interstate at 70mph with about 40 miles of city driving.

When I state 15-17, that is strictly highway mileage. Yes, it is possible to get 15-17 on a tank full if you are at factory weight, not towing, not using winter blend gas, and stay between 50-70 mph for 90% of the time. I have seen 17.1-17.6 on the highway for a 50 loop trip from start to stop doing 55-60.

As for city or towing I will get 8.5-11 depending on the weight, redlights, or mountains.

 

Adaptive learning?

 

This new 6 speed will learn your habits.

 

Don't believe that is the way it works. From the manual, when the battery is disconnected, it relearns it's own shift parameters. Says nothing about the driver's. Perhaps Mark Kovalsky, our resident tranny expert, will chime in a give a better explanation.

This vehicle is equipped with an adaptive transmission shift strategy.
Adaptive transmission shift strategy offers the optimal transmission
operation and shift quality. When the vehicle’s battery has been
disconnected for any type of service or repair, the transmission will need
to relearn the normal shift strategy parameters, much like having to reset
your radio stations when your vehicle battery has been disconnected.
The adaptive transmission shift strategy allows the transmission to
relearn these operating parameters. This learning process could take
several transmission upshifts and downshifts; during this learning
process, slightly firmer shifts may occur. After this learning process,
normal shift feel and shift scheduling will resume.

 

I get 11.3~11.7 HWY 72mph and about 8 towing, no city. My truck shows within a couple tenths of what I calculate at fillup. My drive to work is 60 miles one way and only 7miles city and a couple stop signs, the rest hwy. Tires are same height as stock, have a Jason cap 6"rise, got about 6K miles. When I drive in 4x4 at about 60mph I still get the same mph. about half those miles have been in 4x4.

I'm sick of winter 3 miles of dirt road to pavement and seam to have a 3 to 4 foot snow drift 100yard long in the road every mourning, always windy open farm land. Kids have already missed 22 days of school this year. They will have to go all the way to July now. Sorry just venting!

 

No, I believe the transmission learns the driver's habits rather than its own. Why would it need to re "learn" its own parameters, stored in the transmission ECU? Many vehicles have offered this feature since the mid-late 90's. Basically, if you are the type of driver that is heavy on the throttle, the transmission will, to a point, upshift later and downshift sooner. If you drive for mileage, it will do the reverse. I don't know all the ins and outs of this transmission, but I know some older ZF transmissions could actually calculate for wear occurring in the transmission and alter shifting accordingly. My old 1997 Range Rover shifted smoother than my new truck, despite having 150k miles on it...due to this adaptive strategy.

 

Here are a couple quotes from Mark from other threads.

"The computer DOES NOT learn from your driving habits. That's an old myth that just will not die.

The computer DOES learn how long each shift takes from when the computer commands the shift until it measures that the shift has completed. It then adjusts the pressure for the next time it makes that shift."

"The computer does adjust to the transmission if the battery is disconnected. It never adjusts to the driver."

All due respect, Mark is an ex Ford transmission engineer, I would like to think he knows what he is talking about.

S

 

Fair enough, you're right that he probably would know. However, many cars do have this feature of adapting shift strategy to the driver. Volvo used to have 3 modes on their auto transmissions, selectable by pushbutton: sport, normal, and winter. This was common on Mercedes as well. However, certain VW transmissions claimed they did not require the user to select a mode, the transmission would learn their driving style and create shift points accordingly. Many other carmakers followed suit. I know after the battery is disconnected in the truck, it does not shift as smoothly for a while. Typically, during a shift, the trans ECU will command the engine to temporarily reduce torque by cutting fuel for a fraction of a second, and the shift will be so seamless you can only tell it shifted by watching the tach drop.

 

I think that this is what adaptive learning is, the computer adjust to the load, the more load the longer the shift will take so the computer adjusts the shift. If you pull a lot you can feel it happening, the shifts are firmer and the shift points change.

Denny

 

This is my experience. I also noticed it takes a couple driving cycles after un-hooking from the camper for the shifts to soften and go back to normal.

 

I just drove about 1700 miles over the last week from Missouri to the Florida Panhandle. Mild hills to flat, mostly 70 MPH. I got 14 mpg average with 4.30 gears.

 

ditto, my best highway to date is 16.5, took a pic of 16.3..LOL--my diesel friends don't believe. On that same 16.5 tank, I got to our property of 250 acres, drove around at idle. Idled and charged battery on Jeep to get it started and drove prolly 80 miles city/highway chasing parts a cattle feed. My average dropped to 13.1. not bad for city/highway. Highway for long trip was 75 cruise control. Highway for city has been 80-90mph...20-25 mile trips each way.
I like my 6.2
I am still on the same tanck, truck approaching 10k miles.