Can Someone Explain "Final Gear Ratio"

Discussion in 'GT4 Tuning' started by Spoon Tune, Mar 26, 2005.

  1. Spoon Tune

    Spoon Tune

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    What exactly does setting the final gear ratio higher or lower do compared to the Auto setting directly underneathe it?
     
  2. rk

    rk

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    The final ratio is usually considered seperate from the main transmission, kind of like the front sprocket on a bicycle. Often it is actually on the other end of the driveshaft within the differential; I like to remember the term "4:11 posi", commonly assosciated with built muscle cars, as it refers to the lower ratio, higher leverage, positraction (extremely limited slip) differential gearset. Altering this ratio will trade top speed for acceleration in a very linear relationship, while leaving all the shifting gears relationships unchanged IN PROPORTION TO EACH OTHER. Obviously if you set your final to a top speed of 75mph, each transmission gear will have a very short climb compaired to a top speed of 150.
    In an ideal circumstance, you would want to group your transmission gears in such a way that you could keep your engine in the powerband throughout the acceleration portions of the course. A typical gearset for a high horsepower narrow powerband engine might include a very tall first and possibly second gear, since the driver intends to never slow to these speeds, followed by several closely spaced gears, each intended to work just through the sweet spot, handing acceleration seamlessly to its slightly taller sibling, with the tallest topping out at redline at the end of the longest straight. The autoset is just what the name implies, it is a means by which you can approximate the gear grouping effect, it squeezes or widens the individual gear ratios without changing the final. Again, it should be obvious how this can affect top speed and acceleration. If you squeeze your gears to extremely narrow ranges for acceleration, you will quickly use them up and have nothing left for top end.
     
  3. Jmac279

    Jmac279

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    Good explanation :)
     
  4. Velocity

    Velocity

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    That was a good explanation but in simpler terms...

    The final drive determines the ratio of how many revolutions the driveshaft makes to turn the rear differential or tires one turn. So if you have a final ratio of say 4.11 then that means that the for every 4.1 turns of the drive shaft the rear wheels will do one full turn.

    With a ratio of say 3.23 for every 3.23 turns of the driveshaft the rear wheels do one full turn.

    How does this affect acceleration?

    The reason a higher gear number such as 4.11 will help accelerate a car faster is because the engine can spin up faster, getting into and through it's powerband faster and creating more leverage to turn the wheels(this applies to front wheel and 4WD as well) The higher the number the higher the torque multiplication factor.

    I hope this is worded well.
     
  5. Jmac279

    Jmac279

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    It's the number of revolutions it would turn a 1 foot radius ...

    If you have a larger wheel, then it will rotate less (less acceleration, higher top speed) ... if you have a smaller wheel, then it will rotate more (greater acceleration, lower top speed) ...
     
  6. Velocity

    Velocity

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    174
    Yes true but I was just drawing a general picture, rather than throwing to many terms, details and variables to some who might be new to the whole thing.

    I've got friends who just don't know how the hell a car works. It's no shame they've just never been interested or presented a chance before. In fact I have one friend that I have been trying to explain how tire diameter affects top speed too for 5 years and he still can't see it. Maybe he's to simple, I don't know. Maybe I'm a bad teacher! :dopey:

    So I've had to figure out some simple ways of explaining things. Girl friends can be great for that to :tup: That is if you have an exceptional lady who takes interest naturally.
    :tup: :tup:
     
  7. Spoon Tune

    Spoon Tune

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    Dont you mean lower final gear ratios will increase accel because u get more wheel rotations?
     
  8. inferno

    inferno

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    Ok. let me try. It seems you dont understand how gears work. Whan we talk about gear ratios it is implied that after the decimal like 4.11 you have the words "to 1" or "4.11 to 1" What that means is that What that means is that whan the drive gear rotates 4.11 times the driven gear rotates once. Lets say you have two gears exactly the same size. One driving the other. The ratio between the two is 1 to 1 which means they both rotate at the same speed, and the torque applied to the drive gear is the same at the driven gear. Now lets say we have two gears where the drive gear is half the size of the driven gear. in this case the ratio is 2 to 1. Which means, for every two rotations of the drive gear the driven gear rotates once. But now we have a problem. The laws of physics state that energy can neither be created or destroyed. So where the all the work of the drive gear go? Come to find out that this magical setup called an under drive ratio causes a multiplication of the torque applied to the drive gear and although the driven gear only made half the rotations it did so with twice the force. Flip it around and we now have whats called an overdrive ratio. <--A word I'm sure you've heard before. In this setup for every one rotation of the drive gear the driven gear rotates twice. Now where did all those rotations come from. As it turns out, although the driven cog turned twice as far, it did so with half the force.

    Basicaly what that whole speal led up to is that, The higher the labled ratio, (as in 4.11 to 1) the less speed and more power you get. and the lower the ratio, the more speed and less power you will get.
     
  9. jblackrevo9

    jblackrevo9

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    If you raise final gear ratio, you increase acceleration but lose torque and top speed. You want a balance or a advantage depending on which track you will drive.

    For example: test track = set gears not too high or not too low so that the torque and accel assimilate, working together.

    Notice with high gears you can corner better but come out turns slow. Also when drafting someone, if you have nothing but accel, you car will struggle to draft and once it is out of that draft it will lose momentum much more quickly than with torque.
     
  10. jblackrevo9

    jblackrevo9

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    Reminder : Torque gets you car moving while accel gets you to top speed quicker.

    If you have final gear high , it would be wise to increase top speed so that you the top out.

    Ex. 1st gear ranges are 1.723 to 4.567, if you have the gear set at 1.730 , depending on horsepower of car , you will most likely take off slow but at rare occasions you may take off fast with a lot of torque, vice versa if the gear is at 4.555, you are going to have at lot of accel ( crazy wheel spinng varies) but want moves as quick as the other drives who steady moves away because of torque.

    This rule still applies for final gear.