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Rocks and Traction

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  • Rocks and Traction

    It's been a little slow in this section and my time over the past year has been taken up by non-Dodge activities, so I thought I would post some tips for avoiding vehicle damage while traversing trails that are harder to walk over, than drive over.

    Gearing: Off road gearing can seldom be too low. Traditional Dodge highway gears, such as 4.10, is really too high for many situations, where rpm and speed is your enemy.
    Depending upon your daily use, allowances and compromises may be required, but for primarily off road use, gearing needs to be low.
    If you must drive on pavement during the majority of your usage, consider a very low, low range with an acceptable high range and/or overdrive transmission, to give you the best of both worlds.

    Consider all factors when selecting your gearing, engine optimum rpm range, transmission gearing, transfer case gearing, final differential gearing and tire diameter. ALL play an important part in your off road performance.

    In most Dodge trucks, the suspension performance is a tad short of pathetic, so the ability to crawl over obstacles without beating both occupants and vehicle into submission is critical.
    That means the ability to crawl without spinning a wheel, or bouncing off the ground. A successful trip, means you accomplished the trail with little or no damage to parts, tires, or sheet metal and the surest way to do that is by gearing, suspension and tire traction that prevents tire spin, bouncing and vehicle breakage.
    With experience you'll learn the proper tire air pressure to use in various situations and the correct "line" to place your vehicle, to insure the best possible outcome when tackling an obstacle.


    Proper gearing can lessen dependence upon the skinny pedal and prevent part and component failure.

  • #2
    Good job, Norm!
    Power Wagon Advertiser monthly magazine, editor & publisher.


    Why is it that the inside of old truck cabs smell so good?

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    • #3
      A W200 with 727 auto, 203 or 205 t-case & 4.10 axle would have crawl ratio of about 20:1

      Same truck with 435 4-speed drops the crawl ratio to about 54:1

      My W600 with NP540 has an approximate crawl ratio of 100:1 although larger tire circumference negates some of the advantage.

      Good post Norm!

      Bucky

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      • #4
        Aren't the W600s geared with 5.86, 6.17, or lower gears though?

        Crawl ratio is crawl ratio. Of course the tires size can change how the truck 'sees' the ground, because the tire changes the final drive ratio, the effective gear ratio. However, the crawl ratio remains a constant due to the mechanical gearing...so many turns of the engine = so many turns of the wheel. The effective gearing is only another step in the calculation.

        Thirdly, an automatic transmission has some stall built in and because of the torque convertor can mimic having a lower numerical crawl ratio due to viscous coupling.

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        • #5
          Originally posted by rxinhed View Post
          Aren't the W600s geared with 5.86, 6.17, or lower gears though?

          Crawl ratio is crawl ratio. Of course the tires size can change how the truck 'sees' the ground, because the tire changes the final drive ratio, the effective gear ratio. However, the crawl ratio remains a constant due to the mechanical gearing...so many turns of the engine = so many turns of the wheel. The effective gearing is only another step in the calculation.
          Crawl ratio is the effective FINAL gear ratio, including tire diameter, so in effect you almost answered your own question.
          Consider: The crawl ratio of a truck with 5.86 gears and 30" tires, is much lower than a truck with 5.86 gears and 37" tires, so "crawl ratio" does not remain constant due to mechanical gearing, only "differential ratio" does.

          Crawl ratio is a function of differential gearing, tire diameter, transfer case low range and transmission 1st gear ratio.

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          • #6
            Originally posted by rxinhed View Post
            Aren't the W600s geared with 5.86, 6.17, or lower gears though?

            Crawl ratio is crawl ratio. Of course the tires size can change how the truck 'sees' the ground, because the tire changes the final drive ratio, the effective gear ratio. However, the crawl ratio remains a constant due to the mechanical gearing...so many turns of the engine = so many turns of the wheel. The effective gearing is only another step in the calculation.

            Thirdly, an automatic transmission has some stall built in and because of the torque convertor can mimic having a lower numerical crawl ratio due to viscous coupling.
            Yes W600 either had 6.17 (trucks with Dana 70 front) or 6.80 (trucks with Rockwell front, as mine is). And my 40" tires due negate some of the low gearing. In other words my effective gearing could be even lower with light duty truck sized tires.
            Even if a torque convertor doubled the ratio, the manual trans are still lower geared.

            Bucky

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            • #7
              That was all I was trying to convey.

              W600 axles with 40's would be fabulous on my Ramcharger.

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