This is not really a homework problem per se, it's just a question I thought of when attempting a circular motion problem. Imagine a motorcycle rider negotiating a bend on a level road. The centripetal force is then provided by lateral friction between the motorcycle's wheels and the road. At the same time, in order to avoid toppling into the bend, the rider must tilt his motorcycle into the bend. The condition for rotational equilibrium is net torque = 0, where moments are taken about the centre of gravity of the rider. By taking moments as such, we find that the lateral friction acting on the motorcycle wheels will provide a torque sufficient to counteract the torque acting in the opposite direction due to the normal reaction of the road on the motorcycle. But why take moments about the c.g. ? If you take moments about the point of contact of the motorcycle with the road, for example, you'd find that only one force creates a torque about that axis - the weight of the motorcycle, acting vertically downwards through the c.g. of the rider and cycle. In this position wouldn't the condition for rotational equilibrium be violated? So yeah my question is basically why torques must be taken about the c.g. , and why taking torques about any other point in this situation won't work. I apologise for the wordiness. If my explanation of my problem is unclear I'll try to upload a picture of what I'm talking about. Thanks!