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Ratio 3.36 VS 3.55 on a 2012 KW T660 effects on fuel economy

Discussion in 'Ask An Owner Operator' started by RomanSGI, Apr 27, 2015.

  1. Apr 27, 2015 #1
    RomanSGI

    RomanSGI Light Load Member

    98
    19
    Oct 24, 2011
    Haslet, TX
    0
    Hello everyone!

    I am in the market of buying another truck. It's really hard to find a truck with good specs, (ISX15 485HP with 13 SPD). Ok, so I found a truck that has all the specs I am looking for, but just one problem. The ratio is 3.55. I was looking for 3.36 as one would assume you would have better MPG. This truck for the most part will be OTR pulling a 53' reefer. This truck is at a dealership, I got hold of the previous owner by doing some research. It was previously used to pull a flatbed. Previous owner said they are switching their trucks from KW's to Internationals because of better fuel economy.Well that's a whole another discussion, I want to get a KW because of the build quality. Anyone has any experience of having these trucks with different rear ratios? What type of fuel MPG difference am I looking at?

    Truck will be running on a dedicated route from Stockton, CA to Dallas, TX on i-40 traveling at 68-70 MPH. Truck will be at 80,000 LBS Maxed out one way and with a lightweight 15,000 lbs load on the back haul.

    Specs on this truck I'm considering purchasing: Cummins ISX15 500HP, 13 speed, ratio 3.55

    Looking forward to hearing from ya'll!
     
    RomanSGI, Apr 27, 2015
    RomanSGI, Apr 27, 2015
    #1
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  3. Apr 27, 2015 #2
    blairandgretchen

    blairandgretchen Road Train Member

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    Dec 9, 2011
    South west Missouri
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    I'm thinking on that lane a 3.55 or 3.58 would suit you better with the 13 speed and the weight.

    68-70 mph? If you tone that down to 63-66 mph, might help the MPG a bit . . .

    I'm running N-14 /13speed/3.55 - flatbed and 90 day average is 7.1mpg. KW T2000, 63-67 mph most times.
     
    blairandgretchen, Apr 27, 2015
    blairandgretchen, Apr 27, 2015
    #2
    RomanSGI Thanks this.
  4. Apr 27, 2015 #3
    dannythetrucker

    dannythetrucker Road Train Member

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    May 26, 2011
    everywhere, man
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    What size tires ? You should not assume 3.36 will get better fuel mileage than 3.55, could be total opposite. What matters is what speed you intend to run and what rpm the engine will be at when you run that speed.

    with 3.55 and low-pro 22.5 tires, I think you would be around 1450 rpms @ 64 mph in 13, which may be about perfect with a load on. With the 3.36 and again assuming low-pro 22.5 tires you could probably run 12th and do 1400 rpm's about 60 mph, or 13th 1400-1450 for 70 mph.

    So, if you want to run 64, you may be better off with the 3.55, if you want to run 60 or 70 you may be better off with the 3.36

    I'm just estimating though, there are calculator's but you would really want to run the truck (preferably with GPS checking speed). See where you're at say 55, 60, 65, 70. Because something could have been changed along the way, gears could be different or trans could have an oddball gear in it or something.
     
    dannythetrucker, Apr 27, 2015
    dannythetrucker, Apr 27, 2015
    #3
    blairandgretchen and RomanSGI Thank this.
  5. Apr 28, 2015 #4
    RomanSGI

    RomanSGI Light Load Member

    98
    19
    Oct 24, 2011
    Haslet, TX
    0
    blairandgretchen & dannythetrucke Thank you for your replies! I knew I was missing something in the picture. That's exactly what I was hoping to hear. I should pick up this truck next week. Will post ya'll pictures and details. Once again, thank you very much for your reply! If your ever in the area, i-5 Lathrop - Stockton, CA or Fort Worth, TX I'd be more than happy to buy some beer with Texas Roadhouse steak!
     
    RomanSGI, Apr 28, 2015
    RomanSGI, Apr 28, 2015
    #4
    dannythetrucker and blairandgretchen Thank this.
  7. Apr 28, 2015 #5
    blairandgretchen

    blairandgretchen Road Train Member

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    Dec 9, 2011
    South west Missouri
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    You're too kind. Just let us know how it turns out.

    Hey Danny ! We're missing out on an opportunity here! Apparently the nuts and bolts that rattle around our empty skulls actually passes for knowledge, AND, can be turned into BEER!
     
    blairandgretchen, Apr 28, 2015
    blairandgretchen, Apr 28, 2015
    #5
  8. Apr 28, 2015 #6
    dannythetrucker

    dannythetrucker Road Train Member

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    the bone in Ribeye at TX Roadhouse is a #### fine steak !
     
    dannythetrucker, Apr 28, 2015
    dannythetrucker, Apr 28, 2015
    #6
  9. Apr 28, 2015 #7
    Aleeex

    Aleeex Light Load Member

    150
    78
    Jun 8, 2014
    Sacramento
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    I've run mostly volvo with cummins.. but my experience is that 3.36 with 13sp on 22s dies out way too easy on hills. And mpg was HORRIBLE (but i was hauling an 8 car hauler. Average gross 73k) Not sure if the truck was not up kept or what..


    but my isx 550 13sp on 22s with 3.58 is a pleasure to drive. At 70mph I'm at 1500rpm. And rarely do I go over that.


    With a dry van and about 30k in the box I'm typically 6.3-6.6mpg
     
    Aleeex, Apr 28, 2015
    Aleeex, Apr 28, 2015
    #7
    2013Maxx Thanks this.
  10. Apr 30, 2015 #8
    gokiddogo

    gokiddogo Road Train Member

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    Mar 5, 2012
    Ontario Canada
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    What was the HP and torque rating of your 3.36?
     
    gokiddogo, Apr 30, 2015
    gokiddogo, Apr 30, 2015
    #8
  11. Apr 30, 2015 #9
    Aleeex

    Aleeex Light Load Member

    150
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    Jun 8, 2014
    Sacramento
    0
    Supposedly 475 raised to 500 and 1850
     
    Aleeex, Apr 30, 2015
    Aleeex, Apr 30, 2015
    #9
    2013Maxx and gokiddogo Thank this.
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