A behind-cab mount puts the loader crane forward of the body and gives equal left/right horizontal and vertical reach, while a rear mount moves the crane to the back of the flatbed and removes most overhead restrictions on hoist height. The decision does not change the published load chart: the same crane model on the same subframe delivers the same capacity figures in either location, because chart capacity is set by the OEM's structural design, not the X-position on the frame [S1][S2].
What does change is geometry, usable deck length, axle distribution, and the type of outrigger that fits. Behind-cab placement is associated with knuckle-boom cranes and A-frame outriggers, while rear corner placement suits stiff-boom service cranes on mechanic and tire trucks; both are widespread in fleet practice [S2][S3].
Working Geometry and Pickup Sectors
Behind-cab mounting uses the forward body space and gives the operator symmetric reach to both sides of the truck, which suits fast-loading and multi-pickup delivery runs where the same vehicle shuttles between stops [S1][S2]. The position keeps the crane close to the operator's cab, which is the standard arrangement for loader cranes on European and Gulf-region flatbed delivery trucks [S5].
Rear mounting, in contrast, changes overhang and pushes the lift point behind the rear axle, opening up full 360-degree hoist space because the boom no longer fights the cab or the headache rack; the trade is a longer rear overhang and a higher rear-axle reaction in transport [S1][S6]. On mechanic trucks the crane typically sits on the right-rear corner to clear the service body, while tire trucks more often use a center-front mount with the box set back [S3].
Deck Length, Cargo Access, and Outrigger Type
Mounting position sets the usable cargo body length: behind-cab eats the forward deck; rear-mount leaves the forward deck free but may create rear overhang and force longer or differently placed outrigger pads [S1]. Behind-cab is typically paired with A-frame outriggers, while street-side and curb-side corner mounts are typically paired with H-frame outriggers, per common service-truck practice [S2].
For side-corner rear mounts (street-side or curb-side), the operator gets longer horizontal and vertical reach to one side of the truck. Curb-side rear-corner placement is the most common configuration on DOT and mechanic trucks because it puts the working arc away from traffic, while street-side rear-corner mounting is less common but is preferred in some LP-gas and residential-construction workflows [S2].
Axle Reactions, Subframe, and Chart Capacity
Capacity is not decided by where the crane sits on the frame; it is decided by the OEM-approved subframe, mounting brackets, and the outrigger spread [S1]. Gross Vehicle Mass (GVM) compliance does not prove every axle condition, and the completed-vehicle mass and per-axle calculation must be done for the actual completed layout, not a generic similar-project photograph [S1].
Mounting brackets cannot be improvised from a similar project: the subframe has to follow the approved crane and chassis design, and outrigger geometry must be calculated against the rated chart, not estimated from pictures [S1]. A field example illustrates the scale: an Auto Crane RBC-5 (electric, 3-ton rating, 14 ft boom, 17.5 in x 17.5 in base) calls for a minimum 14,500 lb GVWR chassis, with a 24 in pedestal tube of 0.75 in wall tied through the flatbed to the frame and manual outriggers added for stability, per a documented owner-install thread [S3].
Decision Matrix: Behind-Cab vs Rear-Mount
Compare the two positions on the four criteria that actually drive a fleet spec, with the trade shown qualitatively where the research does not give a numeric threshold: [S1]
(1) Working sectors: behind-cab gives symmetric L/R reach; rear mount gives full 360-degree hoist space and best reach for one-side work (curb-side or street-side rear-corner) [S1][S2][S6]. (2) Cargo body length: behind-cab consumes forward deck; rear mount preserves forward deck but can extend rear overhang [S1]. (3) Axle loading: rear mount raises rear-axle reaction and shifts more transport mass aft; behind-cab keeps mass closer to the front axle but eats forward deck [S1]. (4) Outrigger and crane type: behind-cab pairs with knuckle boom and A-frame outriggers; rear corner typically pairs with H-frame outriggers and accepts either knuckle or stiff boom; mechanic and tire service bodies favour stiff-boom rear-corner mounts [S2][S3]. For more layout context, see the Truck Crane Body Length and Crane Position Layout spec map.
Use-Case Recommendations by Workflow
Multi-stop delivery and fast-loading routes: pick behind-cab knuckle boom with A-frame outriggers; symmetric reach and short setup time at each stop are the dominant value drivers, and the unit folds to a compact transport envelope [S2][S5]. Mechanic and tire service trucks: pick rear-corner (typically curb-side) stiff or articulating boom with H-frame outriggers; reach goes away from the road and the body stays usable for tools and parts [S2][S3]. Municipal, DOT, and roadside work: curb-side rear-corner mount; the working arc stays on the operator's side of the truck and away from traffic [S2]. For one-sided long reach, street-side rear-corner mount is the choice, used in some LP-gas and residential-construction fleets [S2].
Limits, Failure Modes, and What to Verify
The single biggest failure mode in field retrofits is treating mounting position as a capacity upgrade. A rear mount does not give more chart than a behind-cab mount of the same model; what it gives is geometry, and the engineering controls are the OEM installation drawing, the completed-vehicle mass and axle calculation, and the approved outrigger/subframe package [S1]. On stiff-boom service cranes in particular, a non-level truck on first lift is a common cause of boom and chassis damage, which is one of the reasons articulated knuckle booms dominate behind-cab work [S3].
For the procurement record, request and keep: the mission lift and cargo schedule, the controlled general-arrangement and subframe drawing, the completed-vehicle mass and axle calculation, and the crane installation, function, and commissioning records; do not approve a layout from similar-project photos alone [S1]. The same chassis and crane can serve either position, but only after both layouts are run against the same delivery cases, with transport and relevant setup reactions, including the outrigger arrangement, on the drawing [S1].
For the relevant spec sheets and selection criteria, see truck mounted crane, truck mounted concrete pump, and dump truck.