A modular chassis is provided for an off-road vehicle to improve assembly, servicing, and repairing of a drivetrain of the off-road vehicle. The modular chassis includes a chassis to support components of the off-road vehicle. A front frame module couples with a front of the chassis, and a rear frame module couples with a rear of the chassis. The front frame module supports lower suspension arms of the off-road vehicle by way of inboard bushing joints. The front frame module supports at least a steering gear and a front differential of the off-road vehicle. The rear frame module is a tube-frame structure that supports components of the off-road vehicle. A lower portion of the rear frame module extends rearward and acutely upward to a top frame member that couples with upper side portions of the chassis. Several cross-members impart structural integrity to the rear frame module.