O.C (c8ce317) 55 gallon drum capacity on vehicles

Windows 7

The Capacity for a 55 gallon drum when attached to a vehicle is shown as 110,000 which is is 550 fuel units. 550/15=36.6 gallons
Is the total capacity reduced when attaching it to a vehicle or is it a bug.

EDIT: Thanks for the quick fix Rivet.