6.7L mileage with oversize tires??

[xxbaker]

Totally stock I WAS getting low 18s hand calc. This was when the truck was new and I was driving like grandma ma on valium. Now I get 11-12 around town and 15-16 on the highway. I am gonna take a 3000 mile trip in mid May to Montana. I will do all my milage calcs. with a gps. Your figures are only as good as your speedometer is accurate, so i will use gps which is probably more accurate than the speedo. I will report milage and prices when I get back.
PS this truck still does much better mpg than my 460 one ton ford. What a pig that thing was.

[bam]

just did my calc today on a stock 2007.5. getting 17.7 average. better on hwy.

about the mileage. adding larger tires (within reason) will increase mileage on the hwy and decr in the city. it is exactly the same as adding a higher gear set to get better mileage. ie 3.42 instead of 3.73, etc. Of course, this is provided that you have enough available power to keep it rolling without putting you foot in it and this ignores the loss D/T incr drag D/T wind resistance, rolling resistance of the tires, tire pressure, etc..

My stock jeep rubicon on 35s went up 2 mpg on the hwy but down 3 in the city. AND it's mileage has always been worse than the 6.7! get a good solid 12 in the city

[RAM_89]

see i average 14-16mpg with 35'' toyos, but maybe its because i have a 4.10 rear end?? my buddy has the same truck but with 35'' mud terrains and 3.73 and he is happy if he gets 11-12??? does going from 3.73 to 4.10 that big of a deal!!! and he said i was stupid for getting the 4.10's!!!LMAO

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2008 3500HD Laramie, 6.7L cummins, 6 speed auto, 4.10 rear end, short box, black,lots of chrom, sun roof, nav, rear seat dvd,Bull bar, Line-X, rear tool box. 2.5'' lift kit, 35'' toyos, EDGE/Attitude, airaid stageII. comming soon , 5'' tbe

[bam]

It seems that with the different flashes, gears, turbos, etc on vehicles depending on manufacture date, etc there is no real answer to mileage. I got great mileage when new. The MPG dropped after a flash update and O2 sensor replacement. Now is much improved after a turbo replacment. I guess that's the price we pay for being first with the new engine, etc

[NC4stroker]

I have an 08 mega cab, and when I checked my speedo with the stock tires with my GPS, the speedo was showing 2 mph over actual.

I just mounted some BFG mud terrain KM-2s (285s) and they made the speedo close to perfect with the GPS!

It would seem that the slightly taller tires yielding effectively a taller final drive ratio, would give you a MPG improvement at highway speed.

[BroncoHound]

Originally Posted by CHKelley

redfisherman007-- Thanks for pointing that out. I'm running 3.42's and actually wondering what that will do to my power and mileage once I add 305/70/17 tires.

I know my mileage might go down, hoping I don't see any power loss.

Hey CH,

Being as you have my exact same truck it seems and I am running 325/70R17 tires I think I can shed a bit of light on your scenario.

With your speedometer corrected (that's what my Bully Dog is for, 70mph on the speedometer is 70mph on my Magellan GPS) you will be at 1500 RPMs at 60mph. At 70mph, you will sit around 1750 RPMs. I usually cruise around 62mph on the freeway and can get over 16.5mpg with the Bully Dog set to stock. I haven't yet completed a tank of fuel with the Bully Dog on Tow but, based on how many miles I have on this tank and where my fuel guage is at I would have to say I am sitting around 16.5mpg with a mixed city/highway. I should be taking a 275-mile or so highway trip this weekend to pick up an Edible Arrangement for my mother for mother's day so we will see how she goes with the Tow tune on strictly freeway. I am predicting upwards of 17.5-18 on the highway.

As far as power is concerned, you have no worries. I pulled 12K in my trailer and the bed of my truck with the 325/70R17 tires on it 1400 miles from Kentucky to wayyyy south Texas and I could barely even tell the trailer was back there. She never skipped a beat.

I don't care what anyone else says about the 3.42 gears; i LOVE them. I rarely ever tow more than 10K though, so I suppose if I were maxxing out the GCVWR all the time I would opt for a numerically higher gear ratio. Of course if that were the case I damn sure wouldn't be running 35" tires, either! Hope this helps.

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'08 QC SB 4WD 6.7L/G56/3.42, HBS Level Lift, Thuren Track Bar, SSSSS, 325/70R17 Nitto's, Weatherguard Boxes, Wheel Well Liners, Tailgate Spoiler, Weathertech Vent Visors and Floor Liners, Line-X, Tekonsha P3, Power Pup, Juice w/Attitude, Shaved BlueTec Badge

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Last edited by BroncoHound : 05-08-2008 at 11:21 PM.

[CHKelley]

BroncoHound-- Woohoo!! Thanks for the info. I doubt I'll go as big as 325's, but it's good to know that the 3.42's are good at 12K. I will haul a car trailer only < 5K. Thanks again...

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2008 QCSB 6.7L 4X4 2500 6-speed Mineral Gray

[TexMexCB]

Went to the scrap yard today and my mega weighed 7760 with the fuel gauge on E and me(192#) in the truck i filled up last week i put 34gal in yeah i run it to the bottom today i put 31 gallons($4.15) and had gone 470 miles giving me 14.77mpg avg with 4:10 rear and 35" tires.

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2007.5 4x4 2500 SLT Khaki Megacab 6.7 Bullydog Power Pup/Lorenz Leveling Kit w/ Bilsteins/35x12.50x17Hankook M/T / Riderite airbags /Frontier nerf bars/ 9" headrest screens /Line-Xtra color matched bedliner