Rear ratios

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

  1. NFDDJS

    NFDDJS Light Load Member

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    Jul 8, 2012
    New Hampshire
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    What are you running for a rear ratio?

    I am putting together a truck and thinking about putting a 3.36 rear ratio.
    This truck will be hauling 80k most of the time. We do have 30-40 loads a year that run around 120,000lbs.
    We will be running this truck with 600HP and 2050TQ

    We are looking for what is going to get us good fuel numbers around 70MPH
    We are running 24.5 tires.

    What are you running?
     
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  3. Superhauler

    Superhauler TEACHER OF MEN

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    3.36 wont stand up to the torqe you going to produce hauling heavy not enough metal meshing to spread out the stress. i would go with 3.55 or 3.70. thats just my opinion! if your hauling light then it may work.
     
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  4. gator21

    gator21 Light Load Member

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    Dec 4, 2011
    Norwich NY
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    i think the 3.36's will be ok for your app.you will need at least a 13spd.im runnin 10spd.3.70's on 22lp.my isx is tweaked by PDI to 565 plus@1850 ftlbs on stock tranny.i need to up my clutch and would love a 13od w/3.55's. the 10 spd has too big of a gap between the top 3 gears.the hp/torque makes it a little better but i know its not the best for the trans/clutch.at 65mph im tach'in 1600rpm.if i push it to 1700,nothin slows it down.but i only get 5.6-6.5mpg,.if i stay down @1400/60mph ill get 7mpg.it sucks goin that slow..
     
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  5. Jerzy

    Jerzy Light Load Member

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    Apr 11, 2012
    New jersey
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    Can you swap out a 10 and install a 13 without changing gear ratios???
     
  6. Jerzy

    Jerzy Light Load Member

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    Apr 11, 2012
    New jersey
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    Can you swap out a 10 and install a 13 without changing gear ratios???Just wondering because I have the same setup as you gator21. It's hard as hell to stay under 65!!!
     
  7. gator21

    gator21 Light Load Member

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    Dec 4, 2011
    Norwich NY
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    yeah you can swap it out.ive been pricin it out at vander haags in iowa.the whole deal at their shop out the door is goin to be around 5500.new clutch included.the rears are another3000. i was gonna get the 13od but my isx shat the bed.13000. to clean her up.maybe next year.
     
  8. fortycalglock

    fortycalglock Road Train Member

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    My opinion is I wouldn't go that low, and I have 3.36 rears in my Star now. Loaded to 80k and starting on a decent incline can really be tough. Now if you were running an 18 vs my 13, it might take care of the low end problems. If you run hills or mountains, you will be down shifting quite often, even with that beast of an engine. I think I remember you saying you're running 46k rears so you should be alright with the torque.
     
  9. Cowpie1

    Cowpie1 Road Train Member

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    I have a Columbia glider with a 500 Detroit DDEC IV 60 and an 18 spd and 2.64 rears and have no problem starting off with a 80K load or running two lanes with hills with that same load. I don't lose gears any faster or more on any hills I run compared to a traditional 3.55 rear. I am using Meritor 14x 40K rear axles. I realize this setup is not for everyone, and I wouldn't recommend it for running over 80K, but it works pretty well for 80K or below. And running in direct 16th at road speed, it is averaging 7.52 mpg. Worse was 6.7 pulling near 80K up and down two lane, hilly roads for the majority of that run. And tranny never gets above 150F and usually between 125F and 140F. Same for axles. And engine EGT's never above 900F on even the hardest pulls. I pull right along with others running similar weights and using shorter rear end ratios.

    The key was to run, at normal road speeds, in direct drive (16th) for more efficiency. The senior engineer at Eaton, Bruce Malinson at Pitts Power, and others have shown that there is substantial power loss by running in overdrives. Eaton has shown that there is a 3% power loss to the rear wheels in overdrive, and Malison has stated (not sure if his numbers are totally accurate) that there is a loss of over 40 hp to the rears when running in overdrive. I can confirm that following these guys, and others, advice, my setup is doing great and the mpg numbers are better than most. I took a shot and it worked. Sometimes it does pay to think outside the box.
     
    Last edited: Aug 25, 2012
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  10. NFDDJS

    NFDDJS Light Load Member

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    New Hampshire
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    I will have the super 18 speed in it so if I am correct that is rated for 2250TQ. The motor is a 6NZ C-15 with some of the PDI upgrades so in real world numbers we should be more around 625-635HP and 2100-2150TQ.
     
  11. black_dog106

    black_dog106 Road Train Member

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    Not criticizing you Cowpie, so please, no offense. Fastest gears i have been in is 3.36. I thought they were long legged. I cant imagine 2.64. It must be a different animal to drive? Im glad the new ride is working out for you. Please keep us up to date with the new truck...David
     
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