Originally Posted by jerrybob
That is why I always empty my bladder before heading out.......
For the most part...
Weight costs fuel economy through resistance to accelleration.
Drag has it's greatest impact at speed.
If you drive fast, drag will cost you at speed... and weight, not so much.
If you accellerate hard, weight will cost you more.
Both are, of course, factors.
Drag is the most important (within reasonable limits).
Water in your fresh tank will not likely cost much to carry with good driving habits.
We tow our 13D with fresh water according to anticipated need without regard to weight .
Since we have not yet "needed" gray or black water we try to keep them as empty as possible when traveling.
When we raced SCCA, we had to go to a larger TV when we switched to a closed trailer (from an open) with roughly the same car and spares.
In my experience ...Nothing tows like a Scamp