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Thread: 3.42

  1. #1
    Bobtail Member
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    3.42

    can anyone tell me what having a 3.42 Ratio truck means compared to a 3.5 ect?

  2. #2
    Road Train Member NWMAXI's Avatar
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    it is a little bit higher gear ratio which means higher speed and lower RPM's not much difference between the two

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    Road Train Member 112racing's Avatar
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    a 3.42 means the drive shaft will turn 3.42 turns to one full rotation of the wheel

    same applies to any ratio 3.55 means shaft turns 3.55 times to one full turn of the wheel.

    3.42 would have a higher top speed but less take off power than a 3.55 (not much difference between the two)

    3.55 would have more take off power but a lower top speed at the same rpm

    so when someone says a "higher gear" it means a lower number .......a "lower gear" would be a higher number

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    Trained Monkey MNdriver's Avatar
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    3.42 has less leverage than a 3.55.

    depending on how the entire driveline is set-up with transmission gears and tire size, you can do a LOT of changing of final gear ratio at the ground.

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    You would never notice the difference between a 3.42 and a 3.55 ratio.

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    Quote Originally Posted by Abusumeyo View Post
    can anyone tell me what having a 3.42 Ratio truck means compared to a 3.5 ect?
    You can download the Cummins Powerspec program here: http://www.powerspec.cummins.com/site/home/index.html

    It will give you engine rpm at a given speed for every combination of components(transmission, tires, rear end ratio) you can imagine.

    They used to have a page where you could do it online but have changed their site, so I don't know if it is still available.

  8. #7
    Road Train Member Cowpie1's Avatar
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    Quote Originally Posted by jbatmick View Post
    You would never notice the difference between a 3.42 and a 3.55 ratio.
    Except a 3.42 would be about 50 less rpm on the engine at the same road speed compared to a 3.55.

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    Medium Load Member Starline's Avatar
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    If you have tall rubber (11R 22.5), you can change to lo pro tires and change your final gear ratio by 50 rpm as well which will give you a little better pulling.
    BTW, 3.42 is a Rockwell... ratio 342 358 373 390 391 410 411 430 433 488 529

  10. #9
    Trained Monkey MNdriver's Avatar
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    Quote Originally Posted by MNdriver View Post
    3.42 has less leverage than a 3.55.

    depending on how the entire driveline is set-up with transmission gears and tire size, you can do a LOT of changing of final gear ratio at the ground.
    Quote Originally Posted by Starline View Post
    If you have tall rubber (11R 22.5), you can change to lo pro tires and change your final gear ratio by 50 rpm as well which will give you a little better pulling.
    BTW, 3.42 is a Rockwell... ratio 342 358 373 390 391 410 411 430 433 488 529

    Change tire size.....

    poor mans gear change.

  11. #10
    Medium Load Member last 1's Avatar
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    Quote Originally Posted by MNdriver View Post
    Change tire size.....

    poor mans gear change.
    Costs more to change 8 good quality drives than change gears so I don't think that qualifies as a poor mans gear change. Sometimes a tire change is a better option also.

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