Auto 4 gears vs Manual 5 gears

Discussion in 'Motorized Vehicles' started by notyou, Oct 2, 2009.

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  1. notyou

    notyou Notebook Deity

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    Why do automatics have 4 gears and manuals 5 (as standard)?

    I read on Wikipedia that since they don't need a hydraulic pump to shift gears they can use that space for an extra gear which allows better use of the engine's power. Is there more to it than this?
     
  2. K-TRON

    K-TRON Hi, I'm Jimmy Diesel ^_^

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    It doesnt matter as to how many gears you have, it matters more in the gearing, overdrive and its use.
    In a truck, one would rather have many low end gears such as 20:1 up to 10:1, so towing is good. On a small car, that is not necessary at all.
    If you need more gears, you can throw in an auxillary overdrive if there is space.

    What are the two transmissions in question?

    This site is really good for calculating gearing, rpm and tire size for vehicle mods.
    http://www.onlineconversion.com/bigger_tires.htm

    K-TRON
     
  3. KernalPanic

    KernalPanic White Knight

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    As it was explained to me (by an automotive engineer at an engineering school)
    The gearing and number of gears is also a design choice.

    Automatics shift when the specs say to, and thus only need the gears to shift when they need to shift.

    Humans make choices depending on what the road and necessary acceleration or economy. A person shifting will need a finer selection of choices as what the road and vehicle "feel" like is how they are going to shift.
    The automotive engineer explained that this is scientifically due to margin for error that the automatics do not need.

    Note that even now auto transmissions do not result in the efficiency or control of a skilled driver with a manual... and its not the gearing... its the fact a skilled driver reacts to inputs that experience and skill tell them are GOING to happen.

    As Ktron explained, the number of gears isn't as important as properly transferring the power and efficiency of the engine involved.
     
  4. notyou

    notyou Notebook Deity

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    There are no specific transmissions in question. I guess this is more of a philosophical "why is there the standard of 4 gears (auto) and 5 (manual) for small cars"?
     
  5. SaferSephiroth

    SaferSephiroth The calamity from within

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    Automatics in current cars have 6 gears or even more, the 4 speeds are a thing of the past.
     
  6. aan310

    aan310 Notebook Virtuoso

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    This is basically only as of 09 and 10 cars though...

    As to why they did this? Gas mileage.
     
  7. Red_Dragon

    Red_Dragon Notebook Nobel Laureate

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    AS much as i want to agree with this, its actually untrue.

    Believe it or not subaru STILL uses a 4 speed Auto and some of there vehicles(I know) and none of there current vehicles if am not mistaken, have any automatics that have greater then 5 gears.

    Also Honda and Acura have NEVER had an auto with more then 5 gears. For whatever reason they are still stuck on 5 speed autos....
     
  8. Sodium

    Sodium Notebook Enthusiast

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    some Mercedes are using 7 speed autos
     
  9. Syndrome

    Syndrome Torque Matters

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    In 08(maybe 07) most of the dodges switched to a 6 speed auto.
     
  10. K-TRON

    K-TRON Hi, I'm Jimmy Diesel ^_^

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    Everything in retrospect, there were automatic transmissions in the 70's which had the potential for 10 gears. Today there are double overdrive air shifting 18 speed automatics, for use behind the Volvo Penta MP-8 used in the new Mack Titan, and such
    [​IMG]

    A car can have as many gears as you want, however the most efficient use of the engine's power is at the peak of the torque curve. So essentially if the torque curve is at say 1800 for a diesel, you want cruising speed of 75mph at 1800rpm. In a car, you want cruising speed at 75mph to be say 3500rpm or so.
    There are people who use numerous overdrives. It can add onto fuel economy, but you need to be an experienced driver. If you suck at driving manual, you should stick with an automatic, as it will compensate for human error better than you may.
    I know some guys who cruise at 75mph at 1350rpm. Its quite nice, and very fuel efficient. GM Spicer Overdrives, the best invention ever

    And for Syndrome, to wet himself over new Cummins ISM's :p
    [​IMG]

    K-TRON
     
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