A tank trailer includes front, rear, and transition sections. The front section has a front frame having a front-frame front end, which is at a front-frame height above a surface upon which the tank trailer rests, and a front-frame rear end. The front section includes a cylindrical front barrel coupled to the front frame and having a front-barrel diameter and a front barrel length. The rear section has a rear frame having a rear-frame front end and a rear-frame rear end, which is at a rear-frame height above the surface, and a cylindrical rear barrel coupled to the rear frame, which has a rear-barrel diameter and a rear barrel length. The transition section includes a cylindrical transition barrel coupled to the front barrel and to the rear barrel and a transition-barrel diameter and a transition-barrel length along a transition-barrel height. The front-barrel diameter is the same as the rear-barrel diameter.