Fuel savings
What slowing down and draining tanks are worth
Water is heavy and speed is expensive. See how much your tanks weigh at each level, and, if you give us your MPG, roughly what easing off the throttle saves.
Weights and notes from the original megawattrv.com calculator
Baseline weight
0lb
Tank water, by fill level
Slowing down
What's original, and what's ours
The baseline weights and the notes about each rig shape come straight from the old Megawatt widget. That widget's script was cut off partway through the fifth-wheel section, before any gallon formula was saved. So we don't pretend to have it.
Water weight is simple: 8.34 lb a gallon. The speed estimate is ours, and it only runs when you give it your MPG and check the box. Air drag climbs with the square of speed, and at highway speed drag is most of what a big, flat-fronted rig fights. Treat the result as a ballpark.