Lowering RPM ?

The main problem is 1450 is where a 12.7 looses all its power and falls flat on its face. You will change gears on every small hill you come to if you never get over 62 mph. The Detroit 60 series I have owned always got the best fuel mileage around 1600.

 

going to 11/22.5 would only get you about 50 rpm differance. Going to a 11/24.5 would get you close to what you want. If you went to a 13 spd trans and run it a half gear down that would drop your rpms to below 1400 for 62. I have heard that can cause the trans to run hot though. High gear would put you about 1150 for 62 mph. I think I would look at other ways to try and save fuel. The pay backs on the above options would be a very long time. If they even made an improvement at all.

 

and remember if you change tire and or wheel size, ya gotta adjust your ride height, or you will end up delivering a bridge!

 

would get you to height problems, and who pulls HiCube contaners cant solve this proble reajusting air ride valve!

so all depends on what you tow.

Yeah! and you loose more fuel shifting down on hills. There is no spliter in your tranny and shifting down to 9th you increase RPM too much!

Not only DD60, but Mercedes PLD engines. Driving with lower engine speed is an illusion of fuel ecomomy.
From my experience: newer Mercedes engines calculate value of fuel per revolution (g/rev) and at 1600 rpm this value is lower then at 1200. And curve is flat up to 1800 rpm, then engine is more powerfull but burns too much fuel.

So I'm not sure you'll save fuel. Becouse with bigger tires to keep engine in optimal fuel efficiency you will drive faster and you'll get more drag (ore speed tickerts LOL).

All modern trucks are designed for 50-60 MPH crusing speed. and engine runs with optimal RPM at this speed.

 

That truck was geared like that for a reason. Thats where that engine is most efficent. A 10 direct and 3.07s is where most Schneider National trucks are at and Im pretty sure they watch their fuel milage very closely. The cost of changing is quiet pricey. The easiest way is to replace the whole center section in both rears. Fronts run about $3500 and fears $2500. It would take a long time to recoupe that money in fuel savings and the truck wont pull as good in the hills if you gear it higher.

 

Why can't you just change the crown and pinion gears only??

 

Sure... but shop labor would eat up any savings from buying a used or reman pumpkin...

 

What kind of milage are you getting now? Those look like pretty good specs seeing as how youve got a single axle with a direct drive tranny and the small 22.5's looks like its setup for economy as is.

 

62 mph at 1600 rpm with a 3.07 ratio ?????????????????????
Am I missing something about this ???????????

You sure you don't have another gear you can shift into ????
I don't know but it doesn't sound right unless you meant 4.07 ratio......