ZFW

[Mitchell]

Occured to me the other day that if Max ZFW is all about Spar Limits and weight in the fuselage then why can't you increase your payload by reducing the amount of fuel in your centre/Tail tanks?

[Mark Harris]

If you increase the payload, you need more fuel!

[lammergeier]

There's a limit to how much fuel you can stuff in the wings, and you have to consider how the CofG will travel aft as you generally burn center tank fuel first.

In short, it's still about wing bending relief.

[Techman]

Are you planning on dumping the payload enroute?.
If so then sure you can.

If not consider this, the extra payload would have an impact on the structure during the entire flight, not only on the first 15-20% as would the centre tank fuel.
Perhaps you could increase you payload by as much as 50%, if you substituted the centre tank fuek with extra payload, but perhaps you would reduce the airframe service life by 50%