Can anyone explain Gearbox Ratio's

Discussion in 'Tech/Mech General' started by fred flintstone, Aug 14, 2016.

  1. fred flintstone

    fred flintstone Funster

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    I have a Peugeot Pilote with a 5 speed box.
    I recently replaced the 5th gears.
    The gears in my box were 33/56 which is 0.59/1.
    The only replacements I could get were 35/58 which is 0.60/1 (approximately 3% lower geared).

    My question is will I have more torque with the new gears or will it be a longer gear giving a higher top speed.

    Maths was never my strongest subject :rolleyes:
     
  2. Boringfrog

    Boringfrog Funster

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    If it's lower geared you will have a lower top speed and it will feel like you have more torque.


    I think o_O
     
  3. John Laidler

    John Laidler Funster

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    It is higher geared, but it may not mean you will go faster, just very slightly lower revs for the same speed. But the difference in your case is negligible I think, 0.59 versus 0.6 is nothing.

    I'm assuming the smaller gear is the input one and it isn't an "overdrive", in which case the reverse* would hold.

    *no pun intended!
     
    Last edited: Aug 14, 2016
  4. scotjimland

    scotjimland Funster Life Member

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    this reads like a Facebook Puzzle.. :LOL:

    pass.
     
  5. DP_JAY

    DP_JAY Funster Life Member

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    Should those numbers not be the other way round?
    56/33 = 1.69 - 1
    58/35 = 1.65 - 1
    Your new gears are lower/ shorter which will mean higher revs and the feeling of more power in fifth,though on!y very slightly.
    I went from 1.7-1 to 1.54 -1 which made a difference of 800rpm @ 60mph.
     
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  6. John Laidler

    John Laidler Funster

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    Which was my point, which is the input gear? I know nothing about pug gearboxes but I understand mechanics. :)
     
  7. Boringfrog

    Boringfrog Funster

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    What do you mean input gear? I think the smaller gear drives the driveshafts.
     
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  8. John Laidler

    John Laidler Funster

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    If that is so, and I have no reason to doubt you, then the arrangement is the opposite of what I thought. By input I meant the gear which is being driven by the engine which in turn drives the gear connected through the final drive the wheels.
     
  9. chaser

    chaser Funster

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    No nowt other than old cars always quoted gear ratios for some reason and top was always 1-1 then overdrive started coming in and it got as it was 1-25 or so as I say don't know owt about it other than that but it must have something to do with it.
     
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  10. Baycott

    Baycott Funster

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    I don't know why i'm reading this post, I don't understand a word of it :Eeek::blush::confused:
     
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  11. Boringfrog

    Boringfrog Funster

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    I thought I did, not sure now! ;)
     
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  12. Boringfrog

    Boringfrog Funster

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    So the gear driven by the engine is the larger.

    Help, my brain hurts.
     
  13. Boringfrog

    Boringfrog Funster

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    fiatmmmgear2.jpg
     
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  14. DP_JAY

    DP_JAY Funster Life Member

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    Yea, as per a bike gearset
    Large gear at front driving smaller gears at rear
    Each time you change to a smaller gear you change to a higher ratio so less turns of the pedals & more turns of the wheel
     
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  15. DP_JAY

    DP_JAY Funster Life Member

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    Yes
     
  16. funflair

    funflair Funster Life Member

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    To answer at least part of the original question it doesn't alter the torque at all as that is a product of the engine characteristics not the gearbox.

    On the gearing it looks me to be a slightly lower overdrive, so a few more revs for the same cruising speed.

    Martin
     
  17. John Laidler

    John Laidler Funster

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    Oops, no, the whole point of the gearbox is to increase the torque at the wheels, the lower the gear the greater the torque. For example, an overall gear ration of 1:2 would double the torque from the engine. Conversely, the higher the gear the lower the torque.

    But to answer @stooo 's question - I wouldn't worry too much. The new gears are indeed a slightly lower ratio but the difference is only 2%, so I doubt you will even notice it.
     
  18. funflair

    funflair Funster Life Member

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    But the engine produces torque via the combustion process which in turn produces power which is the torque X engine speed, the gearbox's job is to match the engines most efficient operating rev range to the desired road speed. Or that's the way I see it anyway.

    Martin
     
  19. JJ

    JJ Funster

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    The ratio of the gear to talc/washing power/Vim that you get for your money is totally dependent on the decency of your supplier/dealer...

    If you talk too much about him, he might be upset.

    I hope this helps.

    JJ :cool:
     
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  20. John Laidler

    John Laidler Funster

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    You are right about torque times revs equals power but the same equation applies at the wheels. So if in a low gear the wheels are turning slowly then the torque at the wheels will be correspondingly higher. It is basically the principal of levers, which is all gears are in a sense. A low gear is like a long lever and the force (torque) it can transmit will be greater. Of course choosing the right gear is also about matching the speed of the engine but torque does not remain constant at the wheels irrespective of the gear chosen.
     
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