gearing vs mpg whats your input???

Daycab, 3:90, 18sp, 22.5 tall, N14 525hp, 1500 rpm at 65 mph.......can't say I'm settin the world on fire, but it's ok. If I cruised down the highway for hours on end it might be better. But for now, it's between 5.5 and 7.5.

I wouldn't mind somethin a bit taller...maybe 3:70.

 

a guy in our fleet is running the same truck as you set up wise and he is running 4.7 hauling 105,500 from northern ID to wester WA, i think 3.42 or 3.55 would suit you better than the 3.36 unless you wanna run 75 then go with the 3.36

 

My '95 435HP 5EK/ 15 speed/3.36 has lifetime average of 6.23... pulling flats and vans...

 

What are you hauling and where? i cant speek for everyone but the experience that i've had where i work we are actually seeing better mileage with 4.10's than with 3.90's. i will add that we do not do a lot of highway hauling, i would say 70/30 with the more being two lane roads, lota hills, back roads, comstuction type hauling, (lowboy, dump trailer, walking floor, etc). It seems that the lower gears allow u to select a higher trans. gear dropping rpm. THIS is not true for everyone, most likely not for you, just my .02. we also haul mostly overwieght 107k and up.

 

99 Flat top 379 With 475 hp CAT 390 rears 10 speed and 24 tall rubber.General D66o on Drive axles. 6.6 pulling a flat 75000 to 80000 gross most of the time. 32000 empty. 63 to 67 mph across I-10 Mostly Flat plate steel. This is using my home made APU at night or anytime I am sitting and waiting. Truck has 1,520,000 miles. 400,000 miles on rebuild. If I slow to 57 - 58 I can get 7.2 to 7.3

 

Dont trust what your computer says- I check my mileage after every tank and i get about 0.6-1.4 mpg worse than the computer says. I have 2 trucks and ill give the numbrs for when i pull small loads (tri axle 95 000-105 000 lbs)
-2005 379X-600+ MXS C-15 70in bunk, 244 wb, 18do tranny 4.11 gears (it used to have 3.90's and before that 3.36 and there was very little difference, if any in mileage) runnin' 55-65 mph gettin' about 4.8-5.4 mpg depending on wind and time of year.
-1999 379 EXHD Series 60 12.7L Jimmy, 63in standup bunk, 244 wb, 13 spd, 3.90 rears runnin the same haul, same driver as the other truck averaged in the summer months 6-6.3 mpg and about 5.6-5.8 in the winter. I even got it up to 6.7 once.

These numbers are taken over abut 2.5 years of hauling logs in SE Manitoba, NW Ontario and NW Minnesota on flat land and driving nicely.

 

I also always check every tank full. I don't have a computer that calculates mine.

 

from what ive read the 3406's and c15's are best matched with 3.55 and the acert motors are best matched with 3.36 fro best fuel mileage. 3406/c15 like 200 rpm higher than the acerts for best fuel mileage.

 

drop the Peterbuilt and get a freightliner with a detroit motor better areodynamics and better fuel mpg. Wont look cool and no need to add chicken light.