ok so i have a 2006 2500 quadcab long bed cummins 6 speed manual...... now eventully i want 5 or 6 inch lift 35's or 37's BF Goodrichs mud or all terrains..... now everyone says once they went to bigger tires they lost roughly 2 mpg i dont understand..... now i do mostly city driving and im getting 15.2 16.2 mpg and 18 all highway... only mods are a cai S&B... now ive also noticed that i get my best milage at 45-55 miles per hour and the faster i go the worse my milge gets.. obviously... being that with the 6 speed your reving past 2000 rpm past 60 now if i switched the 35s or 37s being 5 - 7 inchs taller then the stocky mich 245 70 17s.. per tire rack the stock mich weights 45 lbs per tire... now the bfg's i want are roughly 65 lbs each now i could see the extra 80 lbs of rotational mass to turn but shouldent the added height making the 3.73 gear and fairly low geard 6 speed turn into a pretty high way flyer geard beast? i mean 7 inchs that drops the rpm sicnificatly??? that should keep the rpms lower at freeway speed in theory getting better mpg??? besides the extra weight? and if the weight does offset this what if you took the weight out elsewhere upgrading to beefy alum drive shaft lighter wheels lighter brake rotors?
am i completly wrong or what it just seems like with a taller tire i should expect slightly better mpg or with the added weight the taller gearing should evenout and the mpg shouldent change?

 

the taller tire has more rotational mass which will hurt your mileage. if you had a sports car and put on lighter wheels it would help with throttle response. the fact that you need to get the tires moving is what kills your mileage. I'd bet that going to 35 or 37's will kill your mileage at least 3 mpg.

 

you're only getting 17MPG with a standard? thats pretty **** poor to begin with. Are you hammering on it?

Everyone with a manual diesel no matter what year it is are getting at least 20MPG. One guy who has stock 3.55 gears 9 inches of lift and Tractor trailer tires on it is getting 24 highway and 21 city.

I get better milage than you with my auto tranny

 

Just and FYI, your 2006 2500 has 265/70/17 tires and the 3500's have the smaller 245/75/17

I will have to agree with Steve with you mostly driving in stop and go traffic in the city you will lose around 3 MPG with the bigger tires. You did not say how many miles are on your truck so if it is under 20,000 then it still hasn't got broken in yet.

If you still have low miles on it then load that truck up to a trailer with 6-10,000 Lbs and run it non stop for as long as you can and it will love you for doing so. Well if you don't have a trailer then you could put 2000 Lbs in the bed and run it non stop.

 

the new sticks have such a high final drive ratio it is like you have 4.10's in the axels when you only have 3.73's.

 

wow, that sucks. A lot of my buds went to the standard for fuel mileage.
I have 4:10s with the auto tranny and Ive been around 16-18.5MPG.

but non of my friends have anything newer than an 05 I think

 

the truck has little over 8000 miles i did mean 265 but my keyboard sucks.... i have a s&b CAI thats all ive only towed once i towed my 58 chrysler imperial which weights alot i think 6500 lbs? it self plus the trailer but that was only liek 40 miles away.. dident even feel like i had a car behind me.. i do mostly city to and from work but my girl lives about 35 miles away and i fill up out theere cuz deisel is 30 cents cheaper there then here in the city.. the whole trip there and back is 45mph and 55 mph main streets pretty much no stops and after filling up and driving home i can get my display to read 24mpg when its clder sometimes like 25 26 and after a week of drive back and forth to work all stop and go it goes back down to 15ish and the display is 9times out of 10 dead nuts on when i hand calculate it every fillup... i do beat on it sometimes but not the entire time im driving. esspcially when i drive to see my girl i baby it to get my mpg up... i do use drews brew on most fillups doesnt seem to make a diffrence in milage i can notice it running smoother...i also did get the same milage when it was brand new off the show room floor. hasent rerally gone up any...
can i expect it to get better with more miles????? i do change my oil very often im a maintnace freak and ive changed the oil twice already with 8000 miles 3750 and 7500.. at 7500 i changed the fuel filter which seemed pretty dirty and my milage did not get any better after.. i do plan to chnaged my front read diffs and manual trand an t case fluid to syn at my next service at 11000 miles.. my tire pressures are checked every fillup so those arent low.. you guys thinking theres any thing wrong??? or just need to break in more???

 

I too am getting very $hitty mileage. ( 13 mpg ). With brew without it, oil chnged, fuel filter changed, tires up, same thing. This blows ...

 

Ya have to remember that our Winter fuel gives crappy MPG many have lost 2-3 MPG becasue of it. Yes with more miles you should start to get better MPG.

Like I said load that puppy up and run it for as long as you can non stop to help break it in. I don;t mean just 40 miles, I mean like 1-2,000 miles. These trucks were made to haul/tow heavy loads and if you don't it can take 30,000 miles to get the engine to break in.

When mine had about 1500 miles on it I took it on vacation and drove 30+ hours non stop except for fuel with about 1200 lbs in the bed and the same on the way home and I got over all 18.5 MPG and my best was 20.5 so you can see it does help to run them with a load.

 

well ive really got no where to go to get 1-2000 miles with anything behind be i drove from chicago to iowa about 500 miles unloaded there and brough back parts from a parts car no more then 1000 pounds unless i find a car far far away to buy and bring home i wont be doing any long distance towing... we are adding a 2nd floor and putting up a 5 car garage withiin the next 3 months sooo i will be haulying cement from the house to where ever that will load it down but again will not be long distance i guess il keep driving hell i really dont mind if its not breaking in i hope this will be my last truck il ever have to own i love this thing to death.... proved to be 10000 times more amazing with 12 inchs of snow on the ground this am!
but tanks for the help