I'm worrying about da same thing. I havn't get 2 that yet. But this might help u.The idea is u want a lot of torque. Torque = Force * Lenght. So if your bolt is tighten to 250 (N m) like my Vigor, the length of the cheater bar(in meter) times your weight (if u can use all your body weight as the force) has to be greater than this 250 (N m). However the angle of this force should be at 90 degree with the bar. The closer (to 90 degree) the better.
In this case, Force = your wieght =[ how heavy u are (in kg) * 9.8 (the gravity)]
I'm 150 lbs , so my weight is 66 (kg) * 9.8 (m/s^2) = 647 N
So if I can use half of my weight to pull at 90 degree (the ideal angle) on a breaker bar extended to half a meter, I should be able to get the bolt off.


In reality, there will be other problems, such as the bolt was there too long and it may not be only this 250 (N m) force that I have to overcome.

Among the three factors(the force, the angle, and the length), I think extending the lenght of the bar is the easiest thing to do.

Note: the length depends on the distance from the bolt to where the force is excerted (where our hand is in this case) and the angle the direction of the force made against the cheater bar. The closer u get to vertical, the greater the length. But if the force is horizontal with the bar, the length is zero, thus no torque.


I hope that help.