I just posed this of the fullsize boards, but figured you guys might want to see it

I'm driving home at about 70mph trying to save gas. see how well i can do.
I took the mud terrains off and put them in the bed, threw the brush guard in the bed- got some Highway Terrain style 265/70/17 wheel/tire package. Also put the lower air valence on.

Ohh i go. Sweet,gas milage is worse than when i had a brush guard, no air valence, on MTs and the whole 9 yards. 15.8 mpg. what the ****.

After 2 stops for gas, i said "**** this" and decided to forget the mpg record and shoot for a land speed record. Before going out, I pulled some old motorsports style tricks. I taped up the body gaps, radiator etc. The gaps between the grille, lights, hood, slits in bumper, fog lights, tow hooks. Pulled it up to 80mph and even faster- as high as 110. 17+mpg.

one thing to add: the 17mph range was DEFINATELY the most mountainous

i'm wondering if the 400lbs in the bed (4 tires and wheels and a brush guard) messed up air flow and weighed the rear down too much. I had another 300lbs or so in the cab too.

All I know is i'm driving back at 85mph. I'm leaving the wheels, tires and brush guard at home (not sure about brush guard). We'll see what happens.
I think the gears are just too tall for the 6.0. But the escalade has the same tires, gears, engine etc. I'm also going to put the skid plates back on.

 

Thats wierd for sure guess its the gears liek you are talking about cant think of anything else. With the 5.3 runnin 85-90 from northern AL to Houston I would get get close to 15mpg on 32" all terrains so IDK.

 

I bet it is the extra weight.

 

I would say it was the extra weight. I know just by putting a few CMU blocks in my bed when it snows for soem traction, my MPG will drop a good bit.

 

Did you reprogram the pcm for the different size tires cause that will throw your mileage off.
Also, how are you calculating mileage(by miles per tank, or by the digital readout)?
Either way they will be off if your pcm was not corrected.

 

I corrected for milage, good tought though.

 

going with a larger tire will so to speak change your gear ratio to a higher gear. There is a formula to figure it out but I cant find it any where.

 

alot of that can be in your tuning though. most milage comes from the tune.

 

(Original Tire Diameter / New Tire Diameter) X Original Axle Ratio = Effective Axle Ratio


ok lets say you were running the stock 265 = 30.6 and your mud tires are 305 = 32.8 . I am asumming you have 3.73 gears

30.6/32.8 x 3.73 = 3.479
with 3.479 being your ratio means with the mud tires on your truck would be running a lower rpm at higher speeds which would be better gas milage.

When people put lifts on their trucks and larger tires they ususally change the gears ratio to gain back the power they loose because of larger tires.

 

dude, I even made it bold. I corrected for that and already said that. Believe me, I understand how it works. 112credits deep into a mechanical engineering degree

besides, an uncorrected smaller tire would give false readings that are too high, not too low