But "most" riders other than perhaps racers DO put some weight on their hands. And then there's the weight put on a rider's feet while pedalling. Add to this that as you change from riding in the drops, to the hoods, to the cross portion of a bike with drop bars that you're radically altering the angle of your back and shifting your weight to the rear with each change and any single figure quickly becomes meaningless. Even with flat bars which limit the rider's hand positioning just leaning forward with a bend to the elbows or sitting up straight with locked elbows is going to alter the weight distribution a lot. Then there's the tendency to slide forward during climbing a hill and to slide back during a descent and braking.

So even without bumps and other things just how the rider positions themself from moment to moment is going to cause a sizeable range of weight distribution. Riding a bike is typicaly quite a dynamic exercise.

All of which comes back to wondering why the OP wants this information.