How to Slide Tandems to Adjust Axle Weight

Contents

• What sliding tandems changes
• What it does not change
• A worked example
• Conservative adjustment workflow
• State and route checks
• Sources

What sliding tandems changes

Sliding trailer tandems along the trailer rail moves weight between the drive axle group and the trailer axle group. When you slide tandems toward the rear of the trailer, weight transfers from the drive group to the trailer group. When you slide them toward the front, weight transfers back to the drives.

This redistribution is the tool for correcting an axle-group violation caused by cargo and equipment position — not total weight. It also changes overall axle spacing, which can affect bridge formula calculations for the full combination.

What it does not change

Sliding tandems does not reduce cargo weight, does not create permit authority, and does not make a truck legal if the gross weight, route posting, or permit condition fails. A gross weight problem requires removing cargo or obtaining a permit — tandem position cannot fix it.

A worked example

A truck returns from the scale with:

• Steer: 11,400 lb
• Drive: 35,200 lb (over the 34,000 lb tandem limit)
• Trailer: 31,100 lb
• Gross: 77,700 lb (under 80,000 lb — not the problem)

The drive is 1,200 lb over. Sliding trailer tandems toward the rear of the trailer by about 6 holes (roughly 36 inches) on a standard 6-inch-hole-spacing rail typically moves 1,500–2,000 lb from drive to trailer. After the slide:

• Drive: 33,600 lb (now under 34,000 lb)
• Trailer: 32,800 lb (still under 34,000 lb)
• Gross: 77,700 lb (unchanged)

Both tandem groups now pass. Re-weigh to confirm — the numbers above are estimates; the actual transfer depends on the trailer, the cargo distribution, and the slide distance.

Conservative adjustment workflow

1. Read the scale ticket by axle group: steer, drive, trailer, gross separately.
2. Identify which group is heavy and by how much.
3. Estimate the tandem slide needed — roughly 200–300 lb per hole on most standard trailers, but this varies by equipment.
4. Move tandems within equipment manufacturer limits, shipper instructions, and state legal limits for the route.
5. Re-weigh after the move. The new ticket is the only confirmation that the adjustment worked as intended.
6. Compare each line on the new ticket to federal and state limits for the full route.
7. If any reading remains over legal after adjustment, check permit requirements before continuing.

State and route checks

A tandem adjustment addresses the axle group reading. It does not verify state limits on non-Interstate roads, bridge postings on the route, or permit requirements for the load. State pages such as Georgia, New York, and Washington show how state-specific limits and permit authority apply alongside any scale adjustment.

For reading the scale ticket before deciding on an adjustment — including the correct order for comparing steer, drive, trailer, and gross lines — see How to Read a CAT Scale Ticket.

Sources

This page uses FHWA federal size/weight and bridge formula material for the legal framework. Always check state sources and the current scale ticket before moving.