good ratio for mpg

Discussion in 'Trucks [ Eighteen Wheelers ]' started by hellpatrol, Dec 29, 2016.

  1. hellpatrol

    hellpatrol Light Load Member

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    The hills are on a small portion of what I do,but yes I have to drop a gear or two when climbing. Some hills are over 1 mile long grade. For such a small portion of the total run I will probably be alright, not a lot of traffic at 2am so that's not a problem.
    I also run 22.5's which came with it. If I could switch out the gears out to the as-perfect-as-I-can-get ratio would 355 be better? I run NYC-NJ on I95 for 2 hours, then NY-CT for 4 hours(minor hills). Then CT-MA for 2 hours, that's where the hills are. My weight varies widely from 40K-70+K. I just wondering about the engine stain while climbing. My boost is maxed even when I drop a gear or two. I'm just looking for what's best for the engine in the long term. Fuel secondary and speed last.
     
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  3. Cowpie1

    Cowpie1 Road Train Member

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    Depends a lot on what you do, where you do it, and how you do it. From this spreadsheet on the 3.36 and low pro rubber, it wouldn't be my first choice, but each situation is different.

    Screenshot 2016-12-30_10-15-27.jpg
     
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  4. hellpatrol

    hellpatrol Light Load Member

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    Thanks for the spreadsheet, would you have one for other ratios so I can compare??
     
  5. Cowpie1

    Cowpie1 Road Train Member

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    Give me a ratio you are considering and I can run up a similar sheet in seconds and post it. Here is a few for you.....

    Screenshot 2016-12-30_10-39-02.jpg



    Screenshot 2016-12-30_10-39-32.jpg



    Screenshot 2016-12-30_10-40-13.jpg
     
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  6. hellpatrol

    hellpatrol Light Load Member

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    Awesome, thanks!!!
    I really don't know what would be good. Just want that feel like it's pulling up the hill, not straining just to NOT slow down.
     
  7. Cowpie1

    Cowpie1 Road Train Member

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    Personally, I would use a ratio that gives me what I want for speed at a efficient engine RPM under a full load and do it in 17th gear. Then I would have 18th for those times when I was empty, had a significant tail wind, on flat ground, etc that would let me cruise along at a lower RPM than I would normally pull with to get better economy. For my situation, the would mean something like 3.08.

    Screenshot 2016-12-30_10-47-29.jpg
     
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  8. hellpatrol

    hellpatrol Light Load Member

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    Thank you. This is the what I've been looking for. I haven't worked this week, but next week I'll try it your way and see how I like it,how the truck likes it and where the boost sits for all. I'd be afraid the 3.08 would be a absolute dog on the hills. Then 3.55+ would be too fast(ie gas hog) on the flats. 3.36 I thought would be a good compromise, but it seems the worst for both. Oh joy.
     
  9. Cowpie1

    Cowpie1 Road Train Member

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    Nah. I use an 18 with 2.64 rears and have no problem pulling 46,000 payloads around, even on hills. In this situation, it is the same as 17th with 3.08 but I typically run in 16th direct drive. I can keep up with everyone else and even pass up many company trucks that are similarly loaded. But I am using a Detroit 60 engine. It is all about getting out of the "I need to be in top gear mindset" that gets promoted. The idea is to be running in a gear that offers optimum balance of performance and economy, with some flexibility as situations change. When I am empty and want to "put a wiggle in it" and run 70+ mph, I can then just move on up to 17th and keep RPM's in a more economical range and still have good power. I typically run in the 62-65 mph range for most of the time when loaded.

    2.93 is an option to look at also. Really, all of this has as much to do, like I said, with what you do, where your do it, and how you do it. That is why there is no one size fits all soluton, unlike what fleets think.

    Screenshot 2016-12-30_11-23-38.jpg
     
    Last edited: Dec 30, 2016
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  10. hellpatrol

    hellpatrol Light Load Member

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    With an 18 this gear must send a truck down the road in a hurry! I see from my engine info that the engine is speed limited to 94 mph, which is plenty so I imagine that the limiter would kick in before I even get 16th gear.
    I have to get more stick time to see where the ratio that I have stands, but you are correct in saying we need to get out of the " must be in top gear" mindset. Your charts here will help me see how this run and I'll apply that when I get back on the road next week. I've only filled it up 3 times since I started to haul with it so my info is limited.
    of course there could be something ( hope not! ) with the engine that need to be addressed. I know I'll be pulling off a sensor or two to see how dirty with soot the intake is and if I need to clean it and the sensors.
     
  11. Cowpie1

    Cowpie1 Road Train Member

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