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Gearing Question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by ArrowheadK5, Mar 25, 2002.

  1. ArrowheadK5

    ArrowheadK5 1/2 ton status

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    I know that there is a lot of old posts about this, but I still have a hard time with it, and I don't consider myself stupid, so
    maybe if I just ask again...

    The way I understand, the gear ratio (3.42, for example) is how many times the driveshaft turns for each time the axle (and so the wheels) rotates one time. So, does that mean that a higher gear ratio (4.10, for example) is more for heavy-duty stuff, towing, etc? and so then better with larger wheels? So why would the stock gearing in my 87 k5 be 3.73 and the stock gearing in my 87 k20 be 3.42? Does it also depend on the axles, b/c obviously the 10-bolt in the k5 is different than whatever is in the k20 (d44 or d60, how can you tell?) right?

    Thanks, sorry for the long-windedness.
     
  2. Blue85

    Blue85 Troll Premium Member

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    A higher number is a lower gear. Lower gears give more power because the torque is multiplied by a higher number (more torque at the wheels). Higher gears give better economy (to a point) because the engine is turning fewer rpm for a given speed.

    What gear ratio came in a given vehicle depends on what size tires came on it, the transmission gear ratios, options, etc. Every truck usually has at least 3 options from the factory.

    Yes, lower gears (higher numbers) are better for larger tires since a larger tire is raising your effective gear ratio. A bigger tire makes fewer revolutions to travel a set distance. For example: your vehicle will have the same engine rpm at 60mph with 29" tires and 3.08 gears as it will with 35" tires and 3.73 gears.

    The gear ratio is the ratio of driveshaft revolutions to axleshaft revolutions and it is also the number of teeth on the ring gear divided by the number of teeth on the pinion gear
     

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