Gear Ratio change for fuel savings.

Discussion in 'Car Hauler and Auto Carrier Trucking Forum' started by bmercer, Jul 13, 2017.

  1. bmercer

    bmercer Bobtail Member

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    Rolesville,NC
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    I am thinking of going from a 411 to a 308 or 336 rear. I like to keep up with the speed limit.
    I was thinking of going to a 264 but according to road ranger calculator I would half to be running over 100 mph to get into tenth gear.
    I am looking for fuel savings. Does anyone have any idea what saving it would be or if it would be worth the expense.
    Thanks for any input
     
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  3. KANSAS TRANSIT

    KANSAS TRANSIT Road Train Member

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    Need a LOT more info to even know if its feasible, how much weight do you run at, where do you run, how big a motor you got, is your tranny a direct or over, how tall a tire are you running????? There is a lot to consider other than just grabbing a gear ratio out of the air, you could go to a taller gear and kill your mileage if it works the motor all the time!!!
     
  4. NuCar Carrier

    NuCar Carrier Light Load Member

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    I did something similar once back in the '80s. The results were disappointing. I had a new S model International, 400 Cummins, 13spd. Switched out the 3.73 rears for 3.55. I don't recall the tire size, probably 20.5. It seemed to me the 3.55's were too tall for the 400, it was a dog on hills and couldn't maintain top speed, a bigger engine may have made it work.

    Fuel mileage was the same because I think the engine was working the same even at the lower revs. My thought is a big hp engine that is barely breaking a sweat at 75 mph will get better mileage then a smaller one that's balls to the wall at 65 mph.
     
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  5. bmercer

    bmercer Bobtail Member

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  6. Banker

    Banker Road Train Member

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    From what I have been told it isn't worth the cost to switch unless you have to or have the parts and can do it yourself. I just noticed th 4:11 part. That is a gear one would find in a local rig. You may benefit from the change, who knows.
    I run something very seldom used but recommended by some performance diesel builders. 18 speed with a 2:64. I did it so I can run in direct drive(16) when I am going less than 64. This is the most efficient gear with a one to one ratio meaning less parasitic loss. 17 which is a single overdrive when I need to run. 18 is only to show off which we all know I never would do at this age!

    Walmart uses 2:64 in 10 speeds for fuel mileage with 22.5 tires at 65.
     
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  7. Banker

    Banker Road Train Member

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    I just now remembered that my Jack Cooper rig was a 2:64 10 speed with 19.5 tires and was a hard puller.
     
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  8. bmercer

    bmercer Bobtail Member

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    Sep 27, 2011
    Rolesville,NC
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    Sorry for the previous post. I'm computer illiterate today.
    475 hp @ 1700 rpm,
    1700 lb-ft torque @ 1000 rpm
    24.5" tires
    .73 final drive ratio per international shop. Not direct.
    I will probably gross 60 to 65 k fully loaded.
    It's a 2012 Prostar weighing 18200 full of fuel.
    I'm looking at purchasing a sun country 5 car which is around 17 k with everything.
    I will run all lower 48 but mostly central and southern US.
    The truck at 1600 rpm pulling heavy is running at 65 mph and only getting 4.5 mpg.
     
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  9. KANSAS TRANSIT

    KANSAS TRANSIT Road Train Member

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    20140927_143450 (800x450).jpg Well 411 is a deep gear but 24.5 is tall rubber, could be worse,

    Your truck weighs in at 18,200 and your trailer is 17,000 so you are at 35,000 empty, lets say your load mix is two trucks and three cars ( big load on that trailer but possible) if the trucks are 6500 and the cars are 4000 each you are looking at around 25,000 in cargo so you are only going to be around 60,000 or less most days.

    You could probably go as low as a 3.08 with no issue with your tall rubber I personally would not drop below that if you are running all 48.

    I know you don't want to hear this, but if that Pro Star has a MF in it, I am afraid your gear ratio is going to be the least of your issues, if you already own that truck, I would run it just the way it is and see if it is reliable before I stuck any money into it.

    Don't shoot the messenger, we leased a 2013 Pro Star MF to run a 7/8 car, it was gutless, and it had 342 on 22.5's
     
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  10. Terry270

    Terry270 Road Train Member

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    There's no way I would go under 3.55 but that's just my opinion. Hell with the tall rubber 3.70s would work well. That's what my Volvo midroof has and it averaged 7.4mpg for over 100k miles pulling a Miller 7 car
     
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  11. aussiejosh

    aussiejosh Road Train Member

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    The best idea is to match the right speed to the right revs to get your best economy so if your driving at an average speed of 70mph your ideal revs should be around 1500-1600 rpm for a Cummins so you need to find the right ratio to get your truck to run at those speeds and revs.The only problem with that is when your travelling at say 60 mph you going to have to drop down a gear to get the revs up so either way you going to have an issue.
     
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