How does gear ratio affect Torque


First....What is torque?:

Torque is a twisting force- (it doesn't do any 'work' itself- it is simple an application of energy). 

Work (or 'stuff') happens, when torque is applied and movement occurs.
"Torque is a force that tends to rotate or turn things. You generate a torque any time you apply a force using a wrench. Tightening the lug nuts on your wheels is a good example. When you use a wrench, you apply a force to the handle. This force creates a torque on the lug nut, which tends to turn the lug nut. 

English units of torque are pound-inches or pound-feet; the SI unit is the Newton-meter. Notice that the torque units contain a distance and a force. To calculate the torque, you just multiply the force by the distance from the center. In the case of lug nuts, if the wrench is a foot long, and you put 200 pounds of force on it, you are generating 200 pound-feet of torque. If you use a two-foot wrench, you only need to put 100 pounds of force on it to generate the same torque." 

In summary:
Torque equals Force multiplied by Distance

How does gear ratio affect Torque?
Simply put, torque at work (such as at a wheel) is your motor's torque times your gear ratio.
Motor Torque x gear ratio = torque at the wheel
Lets say we have a 10rmps motor that is capable of 5 oz Torque (we know this from our motor spec.)

Lets say we have 2 gears. Our input gear (attached to our motor) has 10 teeth Our output gear has 50 teeth

Our Gear ratio is 5:1

Motor Torque x gear ratio = torque at the wheel

5oz x 5:1 = 25 oz

What if our gear ratio were 1:3 ?

5oz x 1:3 = 1.6oz

26 Responses so far.

  1. it's really a knowledge full post. thanks to shear . this post has removed my some wrong thing . i thing if you carry on your acctivetice you will achive much popularety.. at last..thanks.
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  2. thank you, my concept about torque are much clear than before.
    continue doing this you will achieve succes in your carrier.

  3. Clint E. says:
    This comment has been removed by the author.
  4. Clint E. says:

    As you wrote above: "In the case of lug nuts, if the wrench is a foot long, and you put 200 pounds of force on it, you are generating 200 pound-feet of torque. If you use a two-foot wrench, you only need to put 100 pounds of force on it to generate the same torque." So, can I understand that bigger engines, like american big block V8s, can generate more torque than smaller engines, whilst they have bigger connecting rods?

  5. Thanks for sharing post. Michelin tyres in Pune are available the best at Shree tyres. The best service in the area and very competitive rates.

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  7. GNA Gears says:

    Hey thanks for the wonderful share and it will be helpful for lot of people. Crown Wheel and Pinion Manufacturers

  8. Unknown says:

    Yes fun w 2 gears so if it were 3 or more is the math the same-
    5:1:5 would be 5.

  9. Thank you for the article , it ‘s really nice and useful
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  10. Unknown says:

    Indeed a very useful information and May Allah bless you for sharing!

  11. Unknown says:

    Indeed a very useful information and May Allah bless you for sharing!

  12. Thanks for the post, hope so that this will help in looking beautiful for longer time.

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  13. Where you get the formula of this:
    "Motor Torque x gear ratio = torque at the wheel"
    you should put citation.

  14. No. 5:1:5 would cancel. Take this example of a 5:1:5. A 40 tooth gear drives an 8 tooth gear(5:1) yeilds 5, but the next change is 8 teeth driving 40 teeth (1:5) yeilding 0.2, the third gear has the same torque as the first because you multiply by 5 then by 0.2 which equals 1, so there is no change. One might ask, "Why bother with such a set-up?" The 3rd gear is rotating in the same direction as the first. If you simple went 40:40 (1:1), while the second gear would have the same torque it would be rotating in the opposite direction.

  15. No. 5:1:5 would cancel. Take this example of a 5:1:5. A 40 tooth gear drives an 8 tooth gear(5:1) yeilds 5, but the next change is 8 teeth driving 40 teeth (1:5) yeilding 0.2, the third gear has the same torque as the first because you multiply by 5 then by 0.2 which equals 1, so there is no change. One might ask, "Why bother with such a set-up?" The 3rd gear is rotating in the same direction as the first. If you simple went 40:40 (1:1), while the second gear would have the same torque it would be rotating in the opposite direction.

  16. Unknown says:

    Hey ive a doubt,what if the smaller wheel were to be run by the bigger wheel,lets say for instance a 22 teeth wheel drives(input gear) a 11 toothwheel(output gear) then wouldn't the torque be more,since for one single rotation of the larger whell the smaller will rotate 2 times?can i get an answer ?

  17. Voldy says:

    Hey ive a doubt,what if the smaller wheel were to be run by the bigger wheel,lets say for instance a 22 teeth wheel drives(input gear) a 11 toothwheel(output gear) then wouldn't the torque be more,since for one single rotation of the larger whell the smaller will rotate 2 times?can i get an answer ?

  18. Voldy says:

    Hey ive a doubt,what if the smaller wheel were to be run by the bigger wheel,lets say for instance a 22 teeth wheel drives(input gear) a 11 toothwheel(output gear) then wouldn't the torque be more,since for one single rotation of the larger whell the smaller will rotate 2 times?can i get an answer ?

  19. Unknown says:

    In a 1:1 would the size of the sprocket make a difference? we adjusted the speed of a machine at work that was #60 chain on a 23t to 16t by swapping the gears... the change was to much. I suggested going 1:1. Any reason to use 23t&23 vs 16t&16t (as far as speed and/or tq?) Thanks

  20. Thanks this was really helpful.

  21. Prime the unit before fitting it and check all components before replacing them - if they're old and worn, they too should be replaced. Don't grip the piston rod with pliers or place the unit itself in a vise, you'll damage it.
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  22. Unknown says:

    I should tell you: everyone in America with the hot rod V8 knows that.

  23. Unknown says:

    Yes, of course. Bigger engines generate more torque than a smaller engines as they have longer links and greater force as well.

  24. What are some good books for this topic... please suggest

  25. Go to www.slideshare.com and look for "The Gear Book" or simpler but product specific "Gears: Lego Mindstorms"

    I would also suggest orderimg some parts for the old Lego Dacta set 1030 and view the construction guides online for set 1031. The best way to better understand gears is to play around with them and Lego provides an excellent beginners hands-on platform.

  26. Thank you for putting forward this important discussion
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