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8 mpg while towing?

2738 Views 10 Replies 7 Participants Last post by  saskboy
hello all, im new here so im sorry if i post this in the wrong section.

my dad purchased his first deisel about three months ago. its a 06 silverado lbz, the truck came with a 6 inch lift 17x10 alloy rims wrapped with 34 inch nitto terra grapplers load d. since then hes added a bully dog tripple dog downloader and a k&n cold air intake to try and help the mileage out. hes only getting 13 mpg back and forth from work (60 mile daily commute) and when we tow our 21 foot toy hauler we're getting 8 mpg. is this normal?
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bully dog and big tires are killing the mileage.
i kinda figured the tires. but the bully dog? what tuner should he go with? would changing the rims to these be better?
Cragar 3975812 - Cragar Soft 8 Wheels - Overview -
The rim size has nothing to do with it, it's the overall tire size. 34" tires will kill your mileage every time, no doubt.

The bullydog tuner is definitely not the best for duramaxes. It has pretty sloppy tuning, there's lots of room for improvement.

If it's all about mileage, not about looks, I'd put the lift down as low as it can go, get some smaller tires, or get some better gears. That combined with a different tuner should get the mileage up some.

another option is to try running in 5th gear in manual mode. That will get the rpms up a little so the engine isn't lugging and sucking down fuel.

Let me know if I can help!

bully dog and big tires are killing the mileage.
Yep – You don’t buy a DMAX if you are looking for Prius mileage but my stock 08 dually with a DPF gets close to 15 light and 9-11 when towing 10,000. You will be able to do a lot better than that with a 06 if you lose the tires and tuner, and keep your Revs in the sweet spot with a light foot. :gearjamin
PPE makes a good tuner for Duramaxes for mileage boosts. The rims don't make a difference, it's the circumference of the tire that is the killer. The bigger the circumference, the more rolling resistence, hence worse fuel mileage. The engine must work harder to turn those big tires around. Think about it...Take a tricycle tire and roll it, then take a truck tire and roll it. It takes much less force to turn the tricycle tire one revolution than it takes to turn the truck tire one revolution.
thanks for the response and the advice :D
If you have the larger tires and do not recalibrate the speedo-- you are traveling farther then you are recording. That will show a lower MPH and lower MPG.

Most tuners will affect the DIC reading-- some will read more and some will read less MPG. So you need to have the speedo corected and hand caculate the mileage driven divided by the gallons pumped into the tank.

Also Winter fuel does not give as good of mileage as Summer fuel.
last summer i was towing my 30' toyhauler getting anywhere from 9-13 depending on what speed I was traveling.
the bully dog tuner has a recalibrater in it thats part of the reason why he got it. dad has always done the mileage by hand. the dash calculations are off by about 1 or 2 mpg
LOL you might as well pull that trailer with a Peterbilt, get the same mileage.
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