Gear Ratios: Misinformation at its worst.

Discussion in 'Experienced Truckers' Advice' started by Hammer166, Apr 28, 2021.

  1. REALITY098765

    REALITY098765 Heavy Load Member

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    The way I see it ,maybe wrongly. is the bigger gear [crown] goes a greater distance for each revolution of the pinion.
     
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  3. REALITY098765

    REALITY098765 Heavy Load Member

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    YES but is it a good idea and can you do that with 456 or 488? On a 488 the crown is thicker but shorter/
     
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  4. God prefers Diesels

    God prefers Diesels Road Train Member

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    I see the disconnect now. In your other post, you were talking about rounding to the nearest thousandth. I thought you were talking about size, but you were talking about decimal points. I thought you were smoking the good stuff there for a minute.
     
  5. Hammer166

    Hammer166 Crusty Information Officer

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    Bigger gear (physically & numerically) takes more revolutions of the pinion to complete one turn, thus does a shorter distance per pinion revolution.
     
  6. REALITY098765

    REALITY098765 Heavy Load Member

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    I agree with this part

    Although I agree with this statement as a fact, but not the conclusion
    The pinion is a constant in terms of rpm where the crown is a variable depending on size. the part that moves the truck wheels goes a farther distance in the same amount of time so ''faster''. with the taller gear.
     
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  7. Hammer166

    Hammer166 Crusty Information Officer

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    Ay Chihuahua! I give up!
     
  8. RStewart

    RStewart Road Train Member

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    I decided to disagree with him after I read an article of his about running in direct vs OD for fuel mileage. I have a 13 with 3.25 rears on low pro 22.5s. my truck runs really good in 12th, .86 ratio, running between 65-67 which is between 1500-1550 RPMs.

    He explained his reasons for direct but they didn't pan out in the real world with my truck.
     
    Last edited: May 3, 2021
  9. RStewart

    RStewart Road Train Member

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    Screenshot_20210503-201134_Chrome.jpg

    Dang, thought I had a triple digit large car.
     
  10. Cat sdp

    Cat sdp . .

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    change rpm to 2050.....:)
     
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  11. Hammer166

    Hammer166 Crusty Information Officer

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    Yeah, you have be geared taller than you are for direct to make any sense.

    I'm geared to run where Detroit recommends for performance, (because carhaul is high duty cycle,) which in my case is 1400 @ 65mph. That's in 13th @. 73, running 3.08 with the little tires we run on the drive. Even dropping to a 2.42 would leave me @1470 rpm in direct, and drop mpg even further into the dismal range.
     
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