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Rear end gears

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Bigmacnchez, Sep 25, 2013.

  1. Bigmacnchez

    Bigmacnchez Member

    I'm running 24" wheels and 32.75" tall tires with my stock 3.73 gears and open diff. I'm wanting to re-gear it. I want either 3.73 to 4.10 with either a 33 or 35 inch tall tire at the end closer to 3.73. I know someone is going to tell me to grab a calculator. Already got one. I guess in my older years I can't remember the formula. Please help lost lots of power from bigger wheels 7" taller.
     
  2. 99'HEARTBEAT

    99'HEARTBEAT Epic Member Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    This Gear Ratio and Tire Size Chart, should be able to help, with which setup "Gears/Tire Size" will give you the Best in Fuel Mileage and/or Performance.

    [​IMG]
     
  3. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

    so here is one formula for gear ratio which can be used to find what you want. There was a thread on it a while back if I can find it.

    (New tire diameter/old (stock)tire diameter) x original gear ratio = New gear ratio

    ie. (35/31) x 3.73 = 4.21
    so if new tire size is 35 and the stock tire was 31 you get 1.129. multiply by gear ratio 3.73. this gives you 4.21 which isnt made. you then need to choose a 4.10 or 4.56. The 4.10 will give you lower highway rpm but you will lose low end grunt. To find your effective gear ratio (so just tire change) just flip the old and new tire sizes.

    Here is a decent online source to just plug it in http://www.4lo.com/calc/geartire.php

    My personal opinion is 4.10 with 33's and go to 4.56 with 35. I basically have your truck in a 4x4 and currently run 4.10 with 35's. Did that mainly as I drove it daily with a large portion of highway, and I can definately tell the difference when I tow. If I start towing more, and its no longer a daily driver, I am considering regearing to get it back closer to the performance of the stock ratio.
     
  4. stchman

    stchman Active Member 1 Year 1000 Posts

    I assume you used that tuner to re-program the ECU for the larger diameter tires?

    My 2008 Silverado I used to own had 20" wheels with 275/55 R20 tires. Those tires were 31.91" tall, I also had 3.73 gears with a 4 speed auto. I noticed no loss in power at all. Granted your current tires are 0.85" taller.

    If you do decide to go with 35" tires, 4.10 gears would be in order.
     
  5. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

  6. McClintoc

    McClintoc ɹoʇɐɹǝpoɯ Staff Member 2 Years 1000 Posts Platinum Contributor

    Silly question but I simply don't know: when you regear the rear end, do you replace just the internal gears or the whole axle?
     
  7. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

  8. JimmyA

    JimmyA Member 1 Year 100 Posts

    Good info! I am wanting to get my truck re-geared. Thanks
     

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