2.62 gear ratio

There is a thread on here titled "My new truck will be......" by ORAM. He went 3.08 with big Cummins and had impressive MPG results.

 

I could be mistakin, but it thought they liked 1400 rpm. Also at a higher rpm you have a bit more power to get over small hills without downshifting. Every time you shift you waste fuel. Lastly i heard, and again, i could be wrong.....that the 17 gear has less resistance then 18 do to how its designed.

 

FYI, According to Kr's book in front of me, his recommendation is 2.79 rear with 13 speed trans running in 11th. KR also recommends you drive slow and since I don't, I think the 2.64 is a great rear if you want to take his recommendation but drive a little faster.

 

You have no idea what you are talking about. You need to STOP giving advice about what you have NO experience about. You are going to cost someone big. What is the low ratio in both 13spd and 18spd? Gokido is looking the right direction. You want the 18B for what you are looking to do. The other thing is to get a not common direct drive trans to keep your low gear, to save your drive line.

 

Holy crap dude! You have got to STOP!

 

I have a 2.95 rear end on my 13spd columbia. It does suck on hills but the MPG is great even when loaded around 76-77k Gross.

 

Not much of a KR fan . 2.79 in 11th would be like 3.90. Can't think of any reason to do that now in 12th that would be like 3.36

 

In 55 MPH States like OR and CA my old truck with 3.36 18 speed got better mpg "busy shifting" @ 57 mph than it did just staying in 17th @ 53 mph.

 

Ok guys I was on my I phone and had people in my ear along with the shop hands needing advice so now that I'm empty and on the lap top here it is.

Ratios relate to revolutions of the tire per mile that's all it is. Ratio aside its revolutions per mile of the tire that get us there. Tire size effects revolutions per mile, so we are gonna use same tire size, eng manufacturer and horse power to be equal there.

A 3.58 ratio takes 3 turns of the pinion to turn the ring .58 of a turn or thousands of an inch past half.
A 2.62 ratio takes 2 turns of the pinion to turn the ring .62 of a turn. Considerable difference this explains to Richter why the drive line turns faster at any given speed with an overdrive gear verses a 1.0 gear. I agree by math the turns per mile equal so close no one should tell. Eveyone asked what are we missing I will tell you. When I said that we couldn't pull the same hill after we didn't need much more reduction. It was a situation that high gear wasn't enough but the next gear was too low. 18 or 13 would help here but an 18918b is the only one that would be close. You say flats mostly wouldn't it suck to have to take a load into the mountains and have to stop on a 6 percent grade due to a wreck with 80000 gross. Be embarrassing if the driveline wrung out getting it started.

A differential is just a gear reduction unit, the more times the drive gear has to turn to make the driven gear make a full revolution the less force it takes.
It also makes it slower.
So in a 1 to 1 setting takes less effort to turn. Back to the math when you raise the rear or final ratio and lower the front enough to compensate or make the same amount of revolutions per mile you have to add a variable in because the higher gear in the back takes more effort to turn. The back or final ratio matters most because that is where power is actually transferred to the ground. Also some will be lost in the driveline the longer the driveline the more is lost. The reason for bigger u joints in the low geared trans and the high geared rear is it takes more torque on the driveline to turn the differential thats connected to the wheel. Where does the drive line get its torque from? The engine via the trans. I also agree wind is constant at a given speed regardless of ratio. But the faster you go the more resistance you have correct. And you all agree to use the 2.62 rear you had to have 1.0 to be as strong as a .73 with 3.58. So at 100 mph a .73 is gonna be able to propel a 2.62 in all that wind. In a 389 Pete at that, the only hope of actually turning that high a gear at that speed is an Aero cab. Now remember he said to make it move if wanted. To max out the engine will need pumped up considerably. Lots of cummins get a nasty hole in the block after that. Its obvious none of you boys have ever drove a big truck. That would be like a ford ranger or s 10 four cylinder five speed. You ever notice you can go faster in 4th gear than 5th its cause it takes hp to beat wind even in a little truck. Now keep in mind its the same truck same rear just different gear selection in the same trans.

As to why you get better fuel economy in 17th at 1400 than 18th at 1200 cause you are pulling its guts out. Richter if you go faster to get the same engine rpm you have more wind, More wind more resistance. Neighborhood of 60mph cant remember exact number is the peak efficiency of the 2.62 driven at 1.0 you have too much drag after that to over come.
The more overdrive you have the faster the driveline spins which builds momentum. Be careful though the faster you spin the pinion the more heat you make in the differential.

Ok boys hope I answereds all your questions but its took an hr to type this as that is some I am not good at.

 

I don't really have a dog in this race, what I do we burn fuel. 6 is great, in fact we would like to help figure it. The question I have is what is the power loss of an over drive transmission in direct vs a 10 direct in direct.