Kingpin-to-Rear-Axle Compliance and Tandem Slide

Whether a trailer's kingpin-to-rear-axle measurement complies with the governing state limit, and how many tandem holes forward it takes to get there. The measurement runs from the kingpin to the CENTER of the rear axle group -- the midpoint between the tandem axles, not the front axle and not the trailer's end -- and states that regulate it do so to control off-tracking through intersections. The limits differ: 40 ft is the well-known California figure, others sit at 41 ft or use a different measurement entirely, and many states do not regulate it at all, so the limit is an input rather than a constant. The catch is what the fix costs elsewhere. Sliding the tandems forward to reduce the measurement moves weight onto the drive axles and off the trailer axles, so a driver who slides four holes forward to get legal in one state can put the drives over their own limit, which is a different violation at the same scale. A trailer measuring 42 ft against a 40 ft limit on 6 in hole spacing is 24 in over and needs ceil(24/6) = 4 holes forward, landing at exactly 40.0 ft. Four holes is a substantial slide -- each hole typically moves several hundred pounds from the trailer tandems to the drives depending on load distribution -- so run the axle-weight check before pulling the pin, not after crossing the scale. A compliance screen; the governing state's own statute and measurement method, and the scale ticket, govern.

excess_ft = kpra_ft - state_limit_ft; holes_needed = ceil(excess_ft x 12 / hole_spacing_in) when the excess is positive; resulting_kpra_ft = kpra_ft - holes_needed x hole_spacing_in / 12.

Kingpin-to-rear-axle-center compliance against the governing state's own limit (40 ft is the California figure; other states differ or do not regulate it), cited by name with the limit entered rather than bundled, and the tandem slide converted to whole holes at the trailer's hole spacing. The governing state's statute and measurement method, and the scale ticket, govern.

The measurement and the slide arithmetic are geometry. The governing limit is entered by the user because it is state law and it differs by state; no state's table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: kpra_ft, state_limit_ft, hole_spacing_in, excess_ft, holes_needed, resulting_kpra_ft, slide_in

• Measurement point kingpin to the CENTER of the rear axle group, not the front axle and not the trailer endstate KPRA statutes
• Limit varies 40 ft in California, 41 ft or a different measurement elsewhere, unregulated in many states; entered, not bundledstate law
• Weight side effect sliding forward moves weight onto the drives; run the axle-weight check before pulling the pincommercial-vehicle scaling practice