rockcrawler304

But also remember for every bit of increase in height also increases the wind turbulence and drag on the under carriage. Not to mention a taller tire is typically wider which also creates more drag at highway speeds. Lowering the RPM with taller tires is the only positive thing. Everything else is a negative for mileage.

Rednax

Taller tires increase rolling resistance. Not a gain, an overall loss. The gain on tires is in a "highway rib" design tread in stock sizing.

ctnv

07.5, 2500,6.7, 4x4, quad cab, hd, 6sp auto, 3.73, thunder rd package, afe/are tonneau,linex,me/wife/fuel+ gross weight of 8k, just hand calculated, 800miles, running 70 to 75 mph, got 16mpg. I can get 19 if I stay 65 or under but I can't drive 65 out west, CA/NV.

mykaos

4x4, leveling kit, 35's (puts truck higher in wind stream w/ more going underneath)(as well tire tread design), gears not matched for tire size, weight & lack of aerodynamics of front bumper and as much as I don't like to admit it, speed. IMO these generally don't start seeing good mpg's until the 100,000 mi + mark. Turn up the electronics to a "performance" setting and drive like there is a egg between your right foot and the pedal.
Pulling a 5'ver of any decent size and trying to run 70++ mph will not get any kind of mpg's.
My 65,000 mi 4x4 gets consistently at least 2 mpg's less than the 235,000 03 2wd I had. Similar performance mods to both.

StroupDog

07 3500 Quad cab long bed 5.9 5" turbo back with Cat deleted. 285/70/17 tires aired up to 65. 103k miles. I did a 500 mile trip trying to get good mileage, empty, fast passed twice on two lane sections. Cruise control set at 63 mph out and 58 back. The trip was not flat and had a couple long grades to pull both ways. Hand calculated 17.8 mpg (lie o meter 21.5) after correcting for the additional 1 inch tire diameter from stock.... 17.8 x 1.03 = overall average 18.334 mpg. (redneck tire size calculation is approx)


Better mileage than the 1990 Toyota 4x4 3.0L 6cyl that wouldn't get out of its own way that this sweet big *** truck replaced.

Txwelder

I keep the tires at 60 PSI, they max at 65. Im trying to make a trip to Texas in January and that will give me a real opportunity to see where the truck performs the best. Ill keep it at 65 and run all the tunes on the DS Predator and then Ill know for sure. I have had more than one person say something must be wrong with the truck. As far as I can tell it coasts very easily. Way better than my 96 did, no where near as well as the suburban.

BLACKBEAR

I get 12.5 with my fifth wheel 38ft total weight when we left home weight was 23.286 trailer 100gal in bed fuel tank tool box wife me and 2 dogs. That is on interstate no wind and no big hills. I do run a wind defector on top of the truck 80lb of air all tires six speed 3.73 gear 62mph 12.5 at 70 10mpg 9 at 75

Rednax

Buddy, I average above 20-mpg around town. Hell, I can pull my 32' travel trailer down the road at 15+ mpg. A CTD is capable of excellent fuel mileage. And I'm not even close to what some other guys are doing. Truck spec is first and foremost on the list of "what is wrong for mpg" (4WD, auto, dually, lift kit, offroad tires, etc); next are climate, terrain and then truck use.

We can't do much about the first (except return it to stock spec with highway tires), but the last holds huge gains. Rolling resistance is key up to 50-mph, and after that it is aero resistance. There is a narrow slot from 1,300 to 1,500 rpm where CUMMINS says best mpg is to be found. At 1,600-rpm on mine I am at 53-mph. I travel the highway at 1,725-rpm, or 58-mph.

The irony, therefore, is that it is possible -- logical -- that the truck will get best fuel mileage around town, not on the highway. The highway simply affords steady state cruise which is harder to achieve around town. But increased driver skill will make that happen. Magic boxes and performance parts are pretty well a waste of money by comparison.

For your "test" go out and confirm an rpm set point for your travel speed beforehand. Make it under 65-mph, not over. You'll want to easily be able to re-set the cruise so use the tachometer, not the speedometer for the travel speed cruise control set point. Once on your trip, don't fill the tank until you've driven at least 30-miles to an hour. Then re-fill prior to shutdown. Just fill to first clickoff, none of that stupid, pointless dribbling. Simple accuracy.

Second day do the same. Drive an hour, then fill. Re-fill near the end of the day with the highway miles nearly done. No driving around town at all. None. Zip. Highway miles only after warm-up, and no miles that include stop signs, traffic lights, etc. Just glide into a station on the highway you've identified before ever leaving town in all cases. Highway fuel station to highway fuel station. This will give your highest present steady state mpg at a given rpm.

Check the basics beforehand. Perfect alignment. Not good, perfect. Tire balance and pressures, too. CAC leaks. New filters. No brake drag. Steering slop is another big one. Note temps, prevailing winds and altitude changes on your logbook. Do the same on the way back, too.

Good luck, and let us know. Enjoy your trip back to Lone Star.

.

DBLR

100% stock with my winter traction tires on empty I can get combo driving 85/15 hwy/city 14-15+ mpg, summer empty with factory Michelin tires at 1600 RPM's/58 MPH I can get 20+ mpg, 18 mpg at 2,000 RPM's/70 MPH, all mpg numbers are hand calculated.

Txwelder

Im driving on the RKL tune right now and the overhead has jumped 2mpg. I dont calculate by the overhead but I pay attention to it. Im anxious to hand calculate the mileage on the higher tune to see if it made a difference. Unless the tune is just messing with the overhead computer, then I can tell it already has.

Of course I cant tow on the 200hp tune but Ill tow on the 100hp tune and should see better than 8mpg if I keep it under 65, which I have been doing since I started this thread.