What is kingpin to rear axle (KPRA)?
Kingpin to rear axle (KPRA / KPRA distance) is the length from the trailer kingpin to the center of the rear axle group. California enforces a 40-foot KPRA limit.
Kingpin to rear axle (KPRA) — sometimes written KPRA distance — is the measurement from the trailer's kingpin (where it couples to the fifth wheel) to the center of the rear axle group. It controls how far the trailer's wheels sit from the tractor, which determines the truck's turning geometry and off-tracking.
Why it matters — the California 40-foot rule
California limits KPRA to 40 feet (California Vehicle Code §35400). A 53-foot trailer whose tandem is slid all the way back can easily exceed 40 ft KPRA and be illegal in California even though its axle weights are fine. The fix is to slide the tandem forward — which also shifts weight onto the drive axles, so the two constraints interact.
LoadLegit's California ruleset checks KPRA natively: it flags a KPRA violation and suggests the exact tandem slide that satisfies both the length rule and the axle limits.
Check a real load in secondsLoadLegit turns axle weights into a pass/fail compliance verdict — federal Bridge Formula plus verified state and Canadian rules — and issues a shareable certificate.
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Related
What is a tandem axle?A tandem axle is two axles spaced close together (typically 40–96 inches) that share a load as one group. The US federal tandem limit is 34,000 lb.What is center of gravity (CoG) in load planning?The center of gravity is the point where a load's weight balances. Its position along the trailer determines how weight splits across the steer, drive, and trailer axles.Axle weight limit checker (federal)Check steer, drive, and trailer axle weights plus gross weight against the US federal limits: 20,000 lb single, 34,000 lb tandem, 80,000 lb gross.