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gear ratios

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 8BaLL, Jun 21, 2002.

  1. 8BaLL

    8BaLL Registered Member

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    How do you guys determine what gear ratio to run for your rig? I am wanting to get some heavier axles but I'm not sure what gear ratio to get them in. Whats a good rule of thumb to go by?
     
  2. Shaggy

    Shaggy 3/4 ton status

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    <font color="green"> What size tires are you running/planning on running in the future, and what transmission do you have? What is the truck used for? Daily driver or just a toy? Do you do any towing? All of this information will help to make an informed recommendation. There are charts and calculators online that can make a recommendation, but nothing beats the experience that alot of the guys in here have.</font color>
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I try and aim for a particular RPM at freeway speed. I don't have overdrive and my motor seems to make great power without being a gas hog up to about 2500 RPM, beyond that much and it starts getting bad mileage.
    There are many online gear vs rpm calculators out there, someone will post a link.

    I'll be running 39.5's with 4.56's soon. 65 mph is gonna be about 2550 rpm depending on the true tire diameter. My current set-up is a little tall right now...3.73's and 36" TSL's. Rpm at 65 mph is a little over 2300

    Rene
     
  4. mplogic

    mplogic 1/2 ton status

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    If you want to stay close to factory RPM and fuel economy (or whatever it currently is), compare the difference in tire size you are going to run to the difference in gear ratio.

    35"/31"= approx 13% difference
    3.73/3.08= approx 21% difference

    The closer these percentages are, the closer to factory specs your rig will be.

    When the difference in gear ratio is greater, the lower your final overall gear ratio, and the better your crawl rate and off the line launches (although higher RPM, lower top speed, and worse fuel economy).

    When tire size difference is greater, the higher your final overall gear ratio will be, better economy and cuising speed, but less off the line "oomph" and worse crawling ability.

    Someone here had a link to great chart. I'm sure they will post it again.
     
  5. Blazer_Boy

    Blazer_Boy 1/2 ton status

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