Rear ratios

Discussion in 'Trucks [ Eighteen Wheelers ]' started by NFDDJS, Aug 24, 2012.

  1. allan5oh

    allan5oh Road Train Member

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    You're right you don't have to use the final gear as your cruising gear, but given that this person can gross 120k and goes across some decent hills, it's better to have more gearing than less. Sure you could do 3.36 gears with 11r24.5 for 70 mph curising and use 12th for 63 mph or so, but that's hard on the driveline at 120k. The poster also stated that they want the best mpg. That's why I recommended 3.73's with 22.5LP tires at 63-65 mph.
     
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  3. Cowpie1

    Cowpie1 Road Train Member

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    You do make a point. But in my case, it is better to have something extra available on top compared to having more than I need on the bottom. Truth be told, the 18 with 2.64's are a good balance. When lighter (35K or under in the box) I make full shifts to the high range just like I did when I was running 3.55's. I can split the bottom as needed depending on the situation with heavier loads. And I still have gears available above. When light or empty, or I want to and it is safe to just let it roll on a downgrade, and I want to step it up and keep the rpms in a good range, I still have gears above to go to so that I am not trying to throw a rod when I kick it up or let it go. One could just use Georgia overdrive, but I don't have to. But I guess if eventually we are all governed to 65 mph like the ATA wants, then it will not matter. But going 75 in 17th at roughly 1475 rpm is better, easier on the engine, and more fuel efficient than trying to do it with 3.73's in 18th. Where your point is valid is only on the bottom end of things and under continuous heavy loading. And I would reiterate what I stated earlier... I would not spec what I did if I was pulling toothpicks out of the forest, or coming out of a soft cornfield grossing 100K with grain. But for 90% of what goes on in trucking on the road, the setup I have would work fine, and has been shown by others to work well.
     
    Last edited: Aug 28, 2012
  4. black_dog106

    black_dog106 Road Train Member

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    One of us is missing something big, here :biggrin_25520:
     
  5. Cowpie1

    Cowpie1 Road Train Member

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    Well, no broken parts yet. Have you pulled gross loads thru Hwy 20 in NW Illinois between Dubuque, IA an Stockton, IL? That is about as good of a test as anything. I have pulled a couple of gross loads thru there with no more issues and just as well as anything I used before. And everyone thinks the hard pulls are only in the rockies. And living a few miles off the hard top, I have pulled several gross loads up and down some rather steep hills on gravel roads, several miles, to and from the house. Unless you mean that you are running into cornfields when you say "off road", then I would agree that pulling, say, 100K in and out of soft cornfield might be an issue. But I never said my setup was for that type of work. I have always made it quite clear that my setup works great for 90% of what trucking is.... 80K or less, with most of that on pavement. And a 7.6 mpg average for the life of the truck, with a few mid 8's thrown in, and the lowest one time mpg of 6.7 on a fill, is all the measure I need to say that this works.

    I realize that there are extreme situations that this would not be the greatest idea. We can always come up with some scenario that would prove a point. But most owners in trucking never take a truck into a forest to pick up toothpicks, haul 70K of grain out of a cornfield, or pull a rock bucket out of the quarry. Not to mention serious heavy haul. And then, there are just some who will never be able to think outside the box. They are comfortable doing it the way it has been done in the past. That's ok too. Where they get it wrong is finding a way to nit pick over something they have no experience with.

    I am not the only one who has this type of setup and is doing well with it. True, there are not a lot of us that have tried it and found out it works well. But the number is growing. But I am also aware, that the majority will blow off this type of setup as goofy. And I have not one problem with that. Also, I will admit, that I was skeptical. Not any more.
     
  6. king Q

    king Q Road Train Member

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    I have always liked a fast diff for lower rpm.
    Where I'm from around 4,1 is normal as most "OTR" trucks gross at about 125 000lbs and normally run at about 60mph.
    I recently got a truck with 4,88 diffs , on a 2000mile round trip with the exact same truck except the other one had 4,1 ratio it was about 9% heavier on fuel.
    It is actually going to be pulling our new RGN when it arrives at up to 220 000lbs so that is why it was specked that way.
    It exits the green band at 50mph in top.
     
  7. KLAUDEC

    KLAUDEC Bobtail Member

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    I had 2.64 gears in mine volvo with 425hp and 13 speed trans going up hills in west virginia with70k next to big550cats 3.55 18 spd. in their petes We was going head to head and they dind understand what the gear ratio can do , and mpg stay allways in mid 7.i miss this truck soon mine warranty is gone i will install eatons 2.64 on W900 and will be single powered axel . PITSBURG POWER they knows what to do to make you truck be very efficiant and they do offer this gears with one powered rearend only .And the second one is domee axel for weigth an mpg .IF I HAUL 120K I WILL GO WITH 3.73 OR 3,90 DEPENDS WHERE ARE YOU RUN.IF WEST I GO 3.90 YOU CAN CHECK CUMMINS GEAR SPECS ON LINE THEY SHOW YOU GEARS TIRE SIZE AND TRANS TO CHOOSE FROM
     
    Cowpie1 Thanks this.
  8. 132hood

    132hood Bobtail Member

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    I have a question is a 10 speed with 3.73 and tall 24.5 is 5hat a good set up
     
  9. 132hood

    132hood Bobtail Member

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    Is 373 with 10 speed 24.5 a good setup running the midwest has a 500 Detroit it's in a freightliner Classic Xl
     
  10. Cowpie1

    Cowpie1 Road Train Member

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    997,520 miles now on my S60 Detroit in front of 18spd and 2.64 diffs. Engine only uses about 1/2 gal of oil in 22,000 miles. Did have to do U-joints and carrier bearing a couple months ago on drive line and decided to do clutch at same time. Was original clutch, still working but didn’t want to go longer on it. Engine still all original.
     
    swaan Thanks this.
  11. Crude Truckin'

    Crude Truckin' Alien Spacecraft

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    Correct me if I'm wrong, but in a 13 or 18 speed, you have countershafts to split the torque going through the transmission, so they can take the higher torque. Direct drive 10 speeds do not have countershafts, making them limited as to how much torque they can handle, but in 10th, it's a 1:1 ratio that's straight through the transmission which is more efficient than a counter shaft transmission, that even though you run it in a lower gear to make a 1:1 ratio, you're still running that power through countershafts, making it less efficient.
     
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