The difference is in the lifting capability.
I use the 30lb wing to carry a single cylinder. I have used 40lb wing for twin cylinders without stage tanks but using that I didn't neeed weights although I do not use a backplate. I use a 50lb wing for tech dives because I carry so much weight on me in terms of the number of tanks.
If you have a 40lbs wing and you add 10lbs body weight, it dos not make the lifting capability of the wing 50lb, but lesser.
ah.. thanks for the great info...

i think i've got it mixed up

.. it is for pulling you up instead of pushing you down ..

so.. one is really heavy .. eg, 250lbs body weight.. and he is carrying 3-4 tanks.... a 50lbs will do him no good then? :-? .. i mean lifting him up...

what do u think... if u r using 40lbs with bp with 3-4 tanks .. is the lifting strength enough?
