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Gearing question 2010 silverado 4.8L

Discussion in 'GM Powertrain' started by rbramhill, Jan 27, 2013.

  1. rbramhill

    rbramhill New Member

    Hey yall, me again

    Just curious i got a 2.5" leveling kit and 33" tires, and now well needless to say my mileage is JUNK :eek:. Just curious im looking at re-gearing the rear end just curious what ratio would be best to go with. I mostly drive city but also a couple times a year do long highway drives and to get to the next town its 80km/h roads. Just curious what yall think.

    Thanks again
  2. vncj96

    vncj96 New Member 1000 Posts

    did you reprogram the computer to adjust for bigger tires. Depending on what your stock size tire was your speedometer could be reading any where from 1-4 mph slower then the actual speed you are going.

    - - - Updated - - -

    If your stocker was 265/70/17 you are going 62 when the speedometer is at 60 3.3% over
    if your stocker was 245/70/17 you are going 64 when the speedometer is at 60 6.7% ovoversold you would need to figure those rates into your mpg. Also it looks like you have a 4x4 so thats double the gears front and rear
  3. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    Plot your original tire size and gear ratio on this chart to see where you fell on it before any modifications. Once done find the similar box for your new tire size. That'll give you a rough SWAG on what gears to use to maintain stock performance with your new tires. You can, of course, adjust to shorter or longer gears from that point to taste ... to sacrifice performance for MPG or vice versa.

    gear-chart.gif

    NOTES:
    Re-gearing won't recover MPG lost to weight and aerodynamic changes that you've made.
    • Those 33's weigh more than your OEM tires did, so you lost MPG (and towing capacity and hauling capacity) because of that weight. If your spare isn't a 33" tire then it can't be used with your other 4 tires, so you can remove it to shed some extraneous weight and recover a little MPG that you lose.
    • By raising your truck you have also adjusted aerodynamic characteristics that hurt your fuel economy. That goofy bumper valence that comes stock under the front fascia adds about 1 MPG to OEM trucks. It's likely -not- doing that for you, anymore. Most people who lift also remove the valence since the truck tends to look tougher without it ... and it's not doing its original job (well? at all? *shrug*) after lifiting. It's designed to be fairly easy to remove/replace so you might experiment with it to see if it makes any difference for you. Mine's long gone...

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