tran ratio

Discussion in 'Trucks [ Eighteen Wheelers ]' started by little cat 500, Mar 19, 2013.

  1. little cat 500

    little cat 500 Road Train Member

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    have a rtlo16618a anybody know what the overdrive ratio is truck has 3.42 rears tall 24's runs 1700 at 70 seams like that alittle high on the rpm
     
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  3. Autocar

    Autocar Road Train Member

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    That is a single overdrive transmission. 17th is your direct 1to 1, 18th is overdrive .86 to 1.
     
    little cat 500 Thanks this.
  4. 25(2)+2

    25(2)+2 Trucker Forum STAFF Staff Member

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    The top gear ratio is .86 from what I have found, a double-overdrive would be 73.

    It's been too long and I didn't run 1 long enough, but I'd say it might be a higher ratio rear gear.
     
  5. Autocar

    Autocar Road Train Member

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    My '88 T600 had a single over 18 with 3.36s and low pro 24.5s. Topped out at 96 mph at 2150 rpm.
     
  6. little cat 500

    little cat 500 Road Train Member

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    ok thanks ill have to swap out the trans
     
  7. Autocar

    Autocar Road Train Member

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    Why? That transmission is more effiecient than a double over. Besides, a double over at .73 to 1, isn't going to gain that much speed and your engine will work harder, to do the same job.
     
  8. little cat 500

    little cat 500 Road Train Member

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    want to get rid of the tall rubber if i go with low 24's it will rev way to high plus the tall rubber is heavy and pricey
     
  9. Les2

    Les2 Road Train Member

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    It was the best thing I ever did was switching to a .73 top gear. My RPM dropped from 1800 to 1500's at 70mph. Motors not turning as fast and gives me a piece of mind.
     
  10. Cowpie1

    Cowpie1 Road Train Member

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    Agree! Single over is more efficient than double over. Direct is more efficient than both! Some forget,ior overlook, that the rear ratio can be changed also to have the final trans ratio one wants to use, with the desired road speed. The senior engineer at Eaton corp was on record at the 2011 MATS that running in direct is 4% more efficient than in overdrive. And even more so than double over. If one wants to get the rpms down, at a desired road speed, going to a taller rear end ratio is a better option in most cases. Not in every situation, for sure, but most cases it is viable. Guess that is why I am running an 18 speed with 2.64 rears. Pulls everything I ask it to just fine, and I am able to pull off high 6 / low 7 mpgs in the winter and high 7 / low 8 mpgs in the summer. I run the transmission in direct (16th) all the time at cruise speed. 1400 rpm is 62 and 1500 rpm is 66 mph.

    If I felt that need for speed, which I do not, I would be turning ball park 100 mph at 1600 rpm on low pro rubber in the top hole with this. Not really sure how fast it would go. The engine tops out at 2100 rpm.
     
  11. Les2

    Les2 Road Train Member

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    For an everyday door swinger you might be right but would be smarter to stick with a 10 direct, less parts turning.

    Personally I'll go with a OD trans with 3.70/3.58 rear so I can use first gear to take off instead of some 2.something entirely too high gear an suffer on take off. a lot of people don't realize this until its too late!

    Cowpies truck is good for highway use and it works for him. Like he said, it won't work for everyone.
     
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