Originally Posted by
Thasiet
This statement is incorrect. A touring bike sees significant torsion loads, above and beyond those experienced by an unloaded bike, due to leverage exerted by panniers mounted at a distance from the bicycle's centerline. More spokes, and to a lesser extent the spoking pattern, affect a wheel's lateral stiffness much more than they do its vertical stiffness. If the main load on a touring bike wheel were vertical, you could tour quite happily on Ksyriums.
The only way that the distance of your panniers from the bicycle centre of gravity could affect wheel torsion would be if you were braking hard with disc brakes. In that case, the height of the centre of gravity of the panniers above the bicycle centre of gravity would add extra torque to the front spokes and be countered by the torque at the disc brake. Other than that, the only effect on wheel torque will be the straight addition of mass (irrelevant of the distance from the centre of gravity) which means you need to pedal harder to accelerate.
The "leverage" effect that you talk about cannot apply any torque to the wheel. The torque you refer to in that case is taken by the bicycle frame, which rests on the two wheel axles. The mass of you and the bicycle creates the opposing torque (like a see-saw) that is holding your panniers up. The axles cannot transmit any torque to the wheels, only the drive train can, and it should be obvious that your panniers are not being held up by your drive train.
If you need further proof, put your panniers on, and lift up each wheel. You will see that they are free to spin; the panniers mass is still there, applying the same leverage as always, but there is no torque being applied to those wheels.