[GlennB0490]

The only real advantage of carrying weight on your back, would be when you are travelling over irregular surfaces out of the saddle. Even then the advantage is tiny.This is going to be a bit difficult to explain, but I will give it a try.Let's say you are strapped into a rigid frame and run over a brick on the road. The entire weight of you and the bike will need to be raised the height of the brick. There is a lot of energy to be absorbed. If you go fast enough, you will probably wind up with a snake bite puncture and a flat spot (or cracks) in the rims.If you imagine repeating the exercise with a (long travel) full suspension mountain bike. The energy needed to get over the brick is significantly reduced. The weight of the wheels and the fixed section of the forks accounts for most of the energy. The rider and the bikes frame move very little. In your case your legs and arms act in a similar manner as the suspension on the mountain bike. So the difference in performance would be the difference between sprung and unsprung weight.There may be another advantage if the extra weight can be used to aid pedaling at low cadences.------------Now if your back pack gives you a better aerodynamic shape that is another story entirely. You can get HUGE advantages from aerodynamic improvements.