⚖️ Axle Weight & Bridge Formula Checker

Type in the scale ticket. This checks every axle group and the federal bridge formula, then tells you which way to slide the fifth wheel or the tandems and how far — in inches and in holes — based on your own wheelbase and trailer geometry, not a rule of thumb.

Scale ticket
How to fix it — optional but worth sixty seconds
Bobtail weights (the tractor on its own, full fuel) let the tool work out the real kingpin load and the pounds per inch your slide actually moves.
Enter the numbers from your scale ticket and press the button. Defaults are a typical five-axle rig, legal and loaded.
Where the numbers come from

Limits (US federal, 23 CFR 658): 20,000 lb on any single axle, 34,000 lb on a tandem (two axles 40–96 inches apart), 80,000 lb gross, and the Bridge Formula B cap on any group of two or more consecutive axles:

W = 500 × ( L×N/(N−1) + 12N + 36 )

where L is the distance in feet between the extremes of the group, N is the number of axles in it, and W is the maximum weight in pounds, rounded to the nearest 500 lb. Below 80,000 lb gross the bridge formula is the binding limit on closely spaced axles; states vary, and grandfather rights and permit weights exist on some routes, so the state you are entering still gets the last word.

Slide maths. The tractor is a beam on two supports with the kingpin load pressing down between them, so sliding the fifth wheel back by Δ moves kingpin load × Δ ÷ wheelbase onto the drives and off the steers. The trailer is a beam on the kingpin and the tandems, so sliding the tandems forward by Δ moves trailer weight × (distance from kingpin to the trailer's centre of gravity) × Δ ÷ (kingpin-to-tandem distance)² off the drives and onto the trailer axles. The tool derives that centre of gravity from your own scale ticket, which is why the answer is in inches and not "a few holes".

EU / UK reference maxima: 10,000 kg on a single non-driving axle, 11,500 kg on a driving axle (13,000 kg with twin tyres and air suspension on some vehicles), 40,000 kg gross combination weight (44,000 kg for a six-axle combination in the UK and for combined-transport operations), with trailer bogie limits of 16,000 / 18,000 / 20,000 kg depending on axle spacing. The plated weights on your plating certificate are the legal ones — these are the defaults, not a licence to load.

Weigh, slide, reweigh. No calculation on a phone outranks a certified scale.