Guides · LoadLegit · 2026-07-02

How to slide trailer tandems to fix axle weight (with the math)

You scaled heavy on the trailer tandems. The fix is usually not unloading — it's sliding the tandems. Here's what's actually happening and how to stop guessing.

The physics in one paragraph

Your trailer is a lever. The kingpin (resting on the tractor's fifth wheel) and the trailer tandems are its two supports, and the load's centre of gravity sits between them. Slide the tandems back and the support moves away from the load's CoG — the tandems carry less, the drives carry more. Slide them forward and the reverse happens. The load never moves; the support points do.

How much weight per hole?

Slider rails have holes typically 4 or 6 inches apart. A widely used rule of thumb is roughly 250–400 lb shifted per hole, depending on hole pitch, trailer geometry and where the load sits. Treat that as an estimate for sanity-checking — the exact number depends on the distance between kingpin and tandems and the load's CoG position.

The exact version

tandem_weight ≈ load × (CoG distance from kingpin) / (kingpin-to-tandem distance)

Move the tandems and the denominator changes — which is why each hole shifts a predictable amount for your trailer and this load. This is exactly the calculation LoadLegit runs: it solves the axle loads from the load's CoG and tells you the precise number of holes to slide, e.g. "slide trailer tandems back 8 holes."

The constraints people forget

• Bridge law: sliding tandems changes your outer-axle spacing, which changes your bridge formula allowance.
• Kingpin-to-tandem laws: several states limit how far back your tandems may sit (kingpin-to-rear-axle distance). Sliding all the way back can fix weight and create a different violation.
• Swing and maneuvering: tandems far back mean a wider off-track in turns.

Check any configuration in seconds with the free calculator, or let the platform compute the slide for you before the truck leaves the dock.