Rippy Productions

Axle weight and tandem slide calculator

Federal limits are 12,000 lb on the steer axle, 34,000 lb on each tandem group and 80,000 lb gross (23 U.S.C. §127). If the drives are heavy, slide the trailer tandems forward; if the trailer tandems are heavy, slide them back. Each hole moves a set amount of weight, about 600 lb on a typical trailer, so divide the overage by that and round up.

Limits: the federal maximums in 23 U.S.C. §127, as applied in TandemIQ. States and permits can impose different ones. Last checked 14 October 2026.

Scale ticket, in pounds

Leave blank to use the sum of the three.

Trailer

Result

Enter steer, drive and trailer weights from your scale ticket.

TandemIQ runs this offline on iPhone and saves the job.

Worked example

Move the tandems 2 holes forward, toward the tractor.

Computed by the same code as the calculator above.

The CAT scale ticket reads steer 11,850 lb, drive 35,200 lb, trailer 31,100 lb and gross 78,150 lb. The trailer moves about 600 lb per hole.

  1. Check each group. The drives are 1,200 lb over 34,000 lb. The trailer tandems have 2,900 lb to spare, steer is 150 lb under, and gross is 1,850 lb under 80,000 lb.
  2. The drives are heavy, so weight has to move back onto the trailer tandems: slide them forward, toward the tractor.
  3. One hole moves 600 lb, leaving the drives at 34,600 lb, still 600 lb over. Two holes move 1,200 lb.
  4. Move the tandems 2 holes forward, toward the tractor. Then re-weigh.
GroupBeforeAfter 2 holesFederal limit
Steer11,850 lb11,850 lb12,000 lb
Drive35,200 lb34,000 lb34,000 lb
Trailer31,100 lb32,300 lb34,000 lb
Gross78,150 lb78,150 lb80,000 lb

Limits, and when to check the rules

  • Always re-weigh after sliding. Estimates only — you are responsible for your load’s legality.
  • Federal limits only. State limits, permits and grandfathered rules can differ, so check the state you are running in.
  • It does not check the bridge formula for your axle spacing, and sliding the tandems never changes steer weight or gross. Those take the fifth wheel or a change to the load.
  • 600 lb per hole is a starting estimate. Real trailers vary with hole spacing and how the load sits. If the slide doesn’t land where it predicted, work out your trailer’s own figure from a before and after ticket.

Save trailers and get the full tool in TandemIQ

Fifth-wheel slide, bridge formula check, calibrated trailer profiles and a ticket log, offline in the cab. Free download with a one-time unlock.

Download TandemIQ on the App StoreTandemIQ details

Questions

Which way do I slide the tandems?

Forward, toward the tractor, moves weight onto the trailer tandems and off the drives. Backward, toward the rear of the trailer, moves weight off the trailer tandems and onto the drives. Slide toward the group that has room.

How much weight does one hole move?

It depends on the trailer. A common starting figure is about 600 lb per hole, which is 6-inch hole spacing at roughly 100 lb per inch. Change the pounds per hole above if you know your trailer’s figure.

Can sliding fix an over-gross load?

No. Sliding moves weight between the drives and the trailer tandems; it never removes any. If gross is over 80,000 lb, or the two tandem groups carry more than 68,000 lb between them, the load has to change.

Why does it ask for gross separately?

A printed ticket’s gross is the official figure, and it can differ by a few pounds from the sum of the axle groups because each group is rounded on the scale. Leave it blank to use the sum.

What does the TandemIQ app add?

The legality check and the tandem slide are free in the app, forever. Scale House, a one-time $4.99 purchase, adds the fifth-wheel slide, a bridge formula check, saved trailer profiles, slide calibration from your own tickets and a scale ticket log.

More free tools

All free web tools or see tools for the trades.