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My Crawl Ratio

Discussion in 'The Garage' started by skidpan, Apr 18, 2006.

  1. skidpan

    skidpan 1/2 ton status

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    So i finally figured it out with a sm465, a np205, 4.56 gears and 39 inch tires i will have a 58.63 crawl ratio. Is this good? should i look into getting lower gears? I have no idea if the is anywhere near good. any one running a simmilar setup? I dont really care about highway speed, as it will be only on the road to anf from the trails. Thanks guys
     
  2. loafer

    loafer 1/2 ton status

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    6.55x1.98x4.56=59.1
     
  3. stallion85

    stallion85 1/2 ton status

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    Here is mine with 3.73's! The SM465 makes a world of difference....I would say that your crawl ratio could def benefit with the addition of the doubler. In all my experience with the SM465 super low crawl numbers I have felt it's good and bad. If you throw a doubler in there you could drive your rig up a straight ledge without even touching the throttle. As of right now my rig will stall pretty easily on the technical stuff and that's with FI added, it was worse with a carb of course.

    If you don't have FI I would highly recommend it! I think your crawl ratio is good considering that someone with an auto and a doubler would be putting around the same numbers if not less....

    New Bitmap Image.JPG
     
  4. noahrob

    noahrob 1/2 ton status Author

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    I am so confused...Did I do this correctly?
     

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  5. stallion85

    stallion85 1/2 ton status

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    looks right to me.....:)
     
  6. 79chevyk10

    79chevyk10 1/2 ton status

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    It is my understanding that a torque convertor is a x2 multiplier on crawl ratios.?
     
  7. stallion85

    stallion85 1/2 ton status

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    Could be right, I know nothing about transmissions......I do know that there is some wicked wheel spin with the 465 in 1st and the xfer case in low. Torque on demand :)
     
  8. 79chevyk10

    79chevyk10 1/2 ton status

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    I hear ya, that granny low first gear is really nice. I have not doubled yet but plan on it in the near future, but one thing I really love about an auto trans is that torque convertor, no stalling, helps with poor tcase/trans gearing. My motor just luggs until the torque convertor flash point and pops right up the obsticle. Although compression braking stinks with an auto without a doubler, you have to hit the torque convertor flash point before you get engine braking, causes me to use my brakes more than I want out on the trail.
     
  9. noahrob

    noahrob 1/2 ton status Author

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    Alright, here comes the really dumb question, the crawl ratio is 70 something revolutions of "Crank, driveshaft, what???" to one revolution of "wheel, what??"
     
  10. koldsimer

    koldsimer 1/2 ton status GMOTM Winner

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    That's the generally accepted number. I have the same drivetrain combo as you skidpan except i'm running 42's. I rarely find that i need any lower gearing around here. On some of the more technical, steep stuff, I have wanted a lower gear to try and creep it but usually a little throttle will solve that. Believe me, unless you are doing real slow technical rockcrawling/trailriding, you will be fine with your current gears.
     
  11. theperfectgarage

    theperfectgarage 1/2 ton status

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    I would want lower gears with that setup, but it depends what you do with your truck. Crawling in the Arizona rocks your gears would be too high. IMO.
     
  12. noahrob

    noahrob 1/2 ton status Author

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    Hey skidpan,

    Sorry to hijack for a minute there...Anyway, I have a sm465/np 205 and 4.56 gears with 35" tires...I would like bigger tires so I can actually go faster that 65 on the freeway, but as far as crawling goes, in 4lo I can mash the gas and go almost nowhere...in fact on several occasions, I just turned to my girlfriend and had a conversation while the tractor (Blazer) rolled up the hill.
     
  13. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    that's good news to me! is this really truth? what exactly is a crawl ratio measuring - practical application?
     
  14. theperfectgarage

    theperfectgarage 1/2 ton status

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    Hey Colby, it's just the " combined lowness factor " of your gears, ( tranny, t-case, doubler and diffs ) . A 80 to one crawl ratio creeps slower at a givin rpm then say a 50 to one ratio. BTW, engineers just refer to it as the " CLF " ratio.:rolleyes:
     
  15. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    6.55 x 1.96 x 4.56 = 58.44:1

    That's the exact combo I currently run and on 39.5's too. I didn't feel any compelling need for a deeper crawl ratio even in Moab...but the 6.2 lugs extremely well.

    Even so I'm almost done putting my next combo together. NV4500/203/205

    5.61 x 1.96 x 2.01 x 4.56 = 100.78:1

    600 engine rpm = 6 tire rpms. Or roughly 61 feet per minute at idle with 39.5's. (.69 mph)

    Rene
     
  16. Chevy305

    Chevy305 6 Lug 14bsf Status Premium Member GMOTM Winner

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    6.55 x 2.08 x 4.10 = 55.8584
     
  17. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Hehe..

    6.55x1.96x2.0x5.13= 132.3:1 :D
     
  18. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    0.73:1... :D

    Rene
     
  19. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    OD would do me no good. Trailer queen only. :)
     
  20. zero cool

    zero cool 1/2 ton status

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    6.56x4.3x4.56 = 128.6:1

    That's just fine for my 37's. :D

    If I had OD, I'd be running 5.89's instead of 4.56's...

    Check out http://www.grimmjeeper.com/gears.html if you want to see how different tranny/tcase/axle gear and tire combinations work together.
     

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