How to Slide Tandem Axles: The Sliding Tandems Cheat Sheet (2026)

Sliding tandem axles is how a driver moves weight between the drive axles and the trailer axles to get legal at the scale. Two things decide whether it works on the first try: which way to slide, and how many holes. The direction rule never changes. The weight-per-hole number changes on every load — and the number most drivers memorize is wrong on roughly half of them.

Key Takeaway

Slide the tandems back and weight moves forward onto the drives; slide them forward and weight moves back onto the trailer tandems. That rule is fixed. How much moves is not. Weight shifted per hole equals the weight currently on your trailer axles, multiplied by the hole spacing, divided by the kingpin-to-rear-axle distance. A 53-foot van carrying 32,000 lb on the tandems with 6-inch holes at a 40-foot kingpin distance moves about 400 lb per hole; the same trailer carrying 12,000 lb moves about 150 lb per hole. Federal limits on the Interstate system are 20,000 lb on a single axle, 34,000 lb on a tandem axle group, and 80,000 lb gross. The procedure is: chock, set trailer brakes, pull both pins, move at walking speed, reseat both pins, then re-weigh before you leave the scale.

The Sliding Tandems Cheat Sheet

This is the whole decision in one table. Read the scale ticket, find your row, slide that way.

If you want the pounds-per-hole numbers laid out for every trailer weight and both common hole spacings, that is a separate table — see our tandem slide chart. This page stays on direction, procedure, and verification.

Which Way Do I Slide? The Only Rule Worth Memorizing

The kingpin is the pivot. The load in the trailer creates a moment about that pivot, and the trailer axle group carries that moment divided by its distance from the kingpin. Move the axle group and you change that distance — which changes how the load splits.

Slide back = weight moves to the drives

Moving the bogie toward the rear increases the kingpin-to-axle distance. A longer lever arm means the trailer axles need less force to hold up the same load, so pounds come off the trailer tandems and land on the drives. This is the fix for the most common scale ticket in the industry: trailer tandems over 34,000 lb, drives with room to spare.

Slide forward = weight moves to the trailer tandems

Moving the bogie toward the nose shortens the lever arm, so the trailer axles pick up more of the load and the drives lighten. This is what you do when a nose-heavy load has your drives over.

Why the rule feels backwards

Drivers get this wrong because the tractor is what physically moves. You pull forward to slide the tandems back relative to the trailer, and you back up to slide them forward. The bogie sits still on the pavement while the trailer frame slides over it. Think in terms of where the axles end up on the trailer, not which pedal you pressed.

How Far? Why "250 Pounds Per Hole" Is Wrong on Half Your Loads

There is no fixed pounds-per-hole number, which is why credible sources quote 250, 375, 400 and 400–500 and all of them are right for the trailer they measured. The relationship is:

Weight shifted per hole ≈ (current trailer axle weight × hole spacing) ÷ kingpin-to-rear-axle distance

Everything in that expression is something you can read off a scale ticket or a tape measure. Worked at a 40-foot (480-inch) kingpin-to-rear-axle distance, which is the maximum permitted in California and a common working setting for a 53-foot van:

Read the left column before you read the rest of the table. Weight moved per hole scales directly with how much weight is already on the trailer axles. Half the load, half the movement per hole. A driver who learned "400 pounds" on a maxed-out van and applies it to a partial load will slide roughly twice as far as intended — and then blames the trailer.

Two more variables move the number. A shorter kingpin-to-rear-axle distance means a shorter lever arm and more weight moved per hole. And hole spacing is a property of your specific trailer: measure it once, write it on the bulkhead, and stop guessing. The full grid across weights, spacings and kingpin distances is in the tandem slide chart.

How to Slide Tandems: Step-by-Step

Step 1 — Weigh and identify which group is over

Get a certified scale ticket with steer, drives and trailer broken out. Without that split you are guessing at both the direction and the distance.

Step 2 — Compute the holes, not the inches

Take the overage on the offending group, divide by your calculated pounds-per-hole, and round up. Example: trailer tandems 1,200 lb over, 6-inch spacing, 32,000 lb on the tandems, 40-foot kingpin distance → about 400 lb per hole → 3 holes back. Under the old per-inch wording that same ticket produced "4 inches," which is less than one hole and would have left the truck roughly 1,000 lb overweight.

Step 3 — Set the trailer brakes, chock, and pull both pins

Pull the red trailer valve. Chock a drive wheel. Then release the slider pins — both sides. If only one retracts, do not attempt to move; forcing it bends the engaged pin and can gall the rail. This is also the moment to place a stopper at the target hole if you use one.

Step 4 — Move at walking speed

Back in the cab, release the trailer brakes and ease forward (to move tandems rearward) or back (to move them forward). Keep it under 2–3 mph. The bogie stays planted; the frame slides over it until the pins line up with the target holes or the assembly meets your stopper.

Step 5 — Reseat both pins and verify by hand

Set the trailer brakes, get out, and confirm each pin has dropped fully into a rail hole. Do not accept a visual glance — pull on each pin. A partially seated pin will hold at idle and walk out under load.

Step 6 — Re-weigh

The formula gives a starting point, not a guarantee. Load position, trailer condition and fifth wheel setting all shift the real answer. A re-weigh fee is trivial next to an overweight citation.

Where Should My Tandems Be? Bridge Formula and the 40-Foot Rule

Axle weight limits are not a single number; they depend on how far apart the axles are. Per the Federal Highway Administration's Bridge Formula Weights guidance, on the Interstate system "single axles are limited to 20,000 pounds," axles "spaced more than 40 inches and not more than 96 inches apart (tandem axles) are limited to 34,000 pounds," and "gross vehicle weight is limited to 80,000 pounds." Groups of axles are additionally capped by the Bridge Formula:

W = 500 × [ L × N ÷ (N − 1) + 12N + 36 ]

where W is the gross weight on any group of two or more consecutive axles, L is the distance in feet between the outer axles of that group, and N is the number of axles in the group. The practical consequence for tandem position: as you slide the trailer axles forward, L between the drives and the trailer tandems shrinks, and the formula allows less combined weight across that group even if each group individually is under 34,000 lb. That is how a truck passes the axle scales and still fails bridge.

Separately, several states cap the kingpin-to-rear-axle distance — 40 feet in California is the one most drivers plan around, which is why the 40-foot figure shows up in every chart. A rear-most position that is legal in one state can be illegal two states later. Route states, not habits, decide the position. Background on federal size and weight rules is in FHWA's size and weight regulations report, and a practical walkthrough of combining fifth wheel and tandem adjustments is covered in Blue Ink Technology's load analysis.

What Actually Goes Wrong: 148 Returns From Our Own Slide Stoppers

We sell a magnetic slide stopper, so we have an unusually direct record of what disappoints buyers. Across the full life of the product there are 148 returns with 68 written comments. Publishing the pattern is more useful than another spec list, because two of the clusters are things a driver can check before ordering anything.

Cluster 1 — The slider rail hole is not a standard size

The largest recurring theme is fit, not failure: "Didn't work for my trailer smaller hole," "Does not fit holes. Advertised it will fit holes," "Doesn't fit all trailers," "Not applicable with my style trailer," "The peg is too narrow and doesn't work properly," and one that cuts both ways — "it was stuck in the hole." Slider rail hole diameter and pitch vary by trailer manufacturer and model year; there is no single dimension that every rail honors. Any peg-style stopper is dimensionally specific. Measure your rail hole before ordering, and treat "universal" claims as a starting point rather than a promise.

Cluster 2 — Magnet expectations exceed what a magnet does

Several comments read as though the tool was expected to arrest a moving loaded trailer: "The magnet not working properly," "No magnetic thing," "This item its not strong enough after doing some research." A magnet's job on a slide stopper is to hold the stopper in place on the rail while you get back in the cab. The stopping force comes from the stopper body bearing mechanically against the bogie at 2–3 mph, not from magnetic attraction. If a listing implies otherwise, the disappointment is designed in. We cover the magnet question in detail in the slide stopper FAQ.

Cluster 3 — Structural failure, small but real

A minority of comments report genuine breakage: "It bent once used," "Fell apart." That is a manufacturing signal, not a usage-education one, and it is worth stating plainly rather than burying. Note this is the distribution of returns that carried written comments — it is not a failure rate, since the large majority of units sold generate no return at all.

Common mistakes That Cost Drivers Money

1. Pulling only one pin

Each side of the trailer has its own locking pin. Pull one, try to slide, and the bogie will not move — force it and you bend the engaged pin or damage the rail. Verify both are fully retracted before you touch the tractor.

2. Moving faster than walking speed

Repositioning with unlocked tandems above 2–3 mph is how bogies run to the end of the rail. Some carriers explicitly prohibit exceeding walking speed for exactly this reason.

3. Using a memorized pounds-per-hole number

Covered above, and it is the most expensive of the Common mistakes on this list because it produces confident, repeated, wrong slides. Calculate from the load actually on the trailer axles.

4. Solving axle weight and ignoring bridge and kingpin rules

Legal on each group is not the same as legal overall. Check the Bridge Formula across the drive-to-trailer span and check the kingpin-distance limit for every state on the route.

5. Not re-verifying pin seating after the move

A pin that looks seated and is not will hold in the yard and release under highway load. Hand-check both. If your pins routinely creep, that is a rail or pin wear problem — see tandem axles that won't stay put.

Doing It Repeatedly: When a Stopper Earns Its Keep

If you haul mixed freight and every load lands differently, the stopper mostly saves trips under the trailer. If you haul the same commodity at the same weight, your target hole barely changes, and a stopper lets you return to it without recounting holes in the dark. The AltitudeCraft Magnetic Tandem Slide Stopper mounts to the steel rail without tools; a step-by-step of the workflow with one in place is in sliding tandems with a magnetic stopper, flatbed and reefer rail differences are in flatbed and reefer fitment, and a magnetic-versus-manual comparison is in best tandem slide stopper tools. Our other trucking and workshop tools are in the full tool collection.

Frequently Asked Questions

Which way do I slide my tandems to take weight off the trailer axles?

Slide them back, toward the rear of the trailer. That lengthens the kingpin-to-axle distance and moves weight forward onto the drives. To do it you pull the tractor forward while the pins are out.

How many holes do I slide to move 1,000 lb?

Divide 1,000 by your calculated pounds-per-hole. On a maxed 53-foot van with 6-inch spacing at a 40-foot kingpin distance that is about 425 lb per hole, so roughly 2 to 3 holes. On a lightly loaded trailer at 12,000 lb on the tandems, the same 1,000 lb takes 6 or 7 holes. There is no universal answer — that is the point.

How far apart are the holes on a trailer slider rail?

Either 4 inches or 6 inches on almost all North American trailers, and it is a fixed property of your trailer. Measure it once. Hole spacing is one of the three inputs to the weight-per-hole calculation, so guessing it wrong scales every subsequent slide.

Can I slide tandems while the trailer is loaded?

Yes, and you almost always do — redistribution is the entire purpose. The cargo and trailer body stay put; only the bogie changes position relative to the trailer.

What if the tandems won't slide?

Check that both pins are fully retracted first. After that the usual causes are rust or debris in the rail, a bent pin from a previous forced slide, or air not fully released to the slider mechanism. Rocking the tractor gently in both directions frees most stuck bogies; forcing it at speed does not.

Does tandem position affect anything besides weight?

Yes. Tandems set rear-most improve high-speed tracking and reduce trailer swing-out; tandems set forward tighten the turning radius for tight docks but transfer more load to the trailer axles. Both are legitimate reasons to move them once you are already legal.

Is a magnetic slide stopper strong enough to stop a loaded trailer?

The magnet holds the stopper on the rail; the stopper body stops the bogie mechanically at walking speed. Nothing in the tool is intended to arrest a trailer at road speed, and no magnet on the market would.

Related Articles

• Tandem Slide Chart: How Much Weight Moves Per Hole
• How to Slide Tandem Axles with a Magnetic Stopper
• Tandem Slide Stopper FAQ: Magnet Strength, DOT Rules, and Fit
• Best Tandem Slide Stopper Tools: Magnetic vs Manual