# Figuring out gear ratios

1. Feb 8, 2009

### ss7

Hey guys, I am trying to determine which gear ratio is best to use for my project. We have 2 cars attached by rope, and whichever pulls the other one on its side, that car wins.

We are given a motor with the following specs:

rpm@torque=3500
rpm stall torque=0.61Nm

So I was wondering if there is a procedure/formula to determine the best gear ratios for optimum torque transfer to the shaft/wheel, considering the given motor specs?

2. Feb 8, 2009

### ss7

Any help guys? or at least links to info? That would be greatly appreciated!

3. Feb 9, 2009

### ank_gl

its not a point of optimum torque transfer, but torque requirement. how much do you think your opponent is going to get? Is other team given the same motor?
Your motor should have more torque than the opponent's(assuming same car size), to pull the other car.

4. Feb 9, 2009

### skeptic2

How much torque is required to overcome breakaway friction? Any torque over that value will be wasted. (In other words, once you start spinning your wheels, more torque won't do you any good.)

5. Feb 10, 2009

### ank_gl

yea that too!! i missed that point

6. Feb 11, 2009

### viperau

If you are having a tugging competition generally the lowest ratio will win, experimenting with the weight of the vehicle to make sure you don`t loss traction to optimise the torque output. keep in mind the fact you will be pulling another vehicles weight, take that into account when you do tests for traction loss.
The best people to talk to would be 4 wheel drive specialists

Last edited: Feb 11, 2009