How to use a CAT scale

What the scale is

A CAT scale is a certified truck scale with three separate platforms in a line, found at truck stops across the country. Each platform weighs independently, so a tractor unit gets its steer axle, drive axles and trailer axles reported separately. For a pickup and a travel trailer, the same three platforms give you exactly the three figures you need.

Certified matters. This is legal-for-trade equipment, checked and sealed. The ticket it prints is a document, not a readout — which is why it settles arguments that no calculator can.

Before you go

• Load the rig the way you actually tow it. Full fresh water if you travel with it, propane on board, bikes on the rack, dog in the back seat, cooler in the bed. A weight taken empty is a weight of something you never drive.
• Fuel to your normal level. Diesel and petrol are heavy, and a half tank against a full one is a real difference on the ticket.
• Bring your five numbers — payload, GVWR, front GAWR, rear GAWR and GCWR. The payload calculator prints a scale card with your targets on it so you can check each line at the kiosk rather than at home.
• Go at a quiet time. Mid-morning on a weekday. You are about to occupy a lane used by people being paid by the mile, and you will need to unhitch.
• Know where you will park the trailer for the second weigh. Look at the site on a map before you arrive.

The two-weigh procedure

1. Weigh coupled. Pull onto the scale with the trailer attached. Put the steer axle on platform one, the truck’s rear axle on platform two, and the trailer axles on platform three. Every axle must be fully on its own platform with nothing bridging a gap.
2. Set the parking brake, stay in the vehicle, and press the call button on the kiosk. Give them a vehicle number if asked — anything you will remember. Do not get out and walk around while it is weighing; people moving about changes the reading.
3. Collect the ticket inside at the fuel desk, or on the app if the site supports it.
4. Unhitch. Park the trailer somewhere legal and out of the way, on its jack.
5. Weigh the truck alone. Steer axle on platform one, rear axle on platform two. Ask for a re-weigh — CAT sites offer a reduced-price second weigh when it follows the first at the same location within their stated window, which is exactly this use case.
6. Keep both tickets. Photograph them. You will refer to them for years.

If the trailer is a fifth wheel or gooseneck, the procedure is identical — the pin weight sits over the rear axle rather than behind it, which changes where the load lands but not how you measure it.

Reading the ticket

The ticket gives you a weight per platform and a gross total. Label them as you read:

• Steer axle — your truck’s front axle. Check against front GAWR.
• Drive axle — your truck’s rear axle. Check against rear GAWR. On a bumper-pull this is the figure most likely to be over.
• Trailer axle — the trailer’s axles together. Check against the trailer’s own GAWR and, with the tongue weight added back, against its GVWR.
• Gross — everything on the scale. Check against GCWR.

The four checks

Getting your true tongue weight

This is the part worth the trip. Take the truck’s total on the coupled ticket — steer plus drive — and subtract the truck’s total on the uncoupled ticket. The difference is your actual tongue weight.

The figures above are an illustration of the arithmetic, not typical values for any particular truck. Yours will differ, and that is the entire point of going.

What to do if a number is over

Do not treat the ticket as a verdict on the trip you are already on. Treat it as data, and work through it in order:

1. Over on the rear axle only? That is a distribution problem. Fit or re-tension a weight-distribution hitch, move bed cargo forward, and shift heavy items in the trailer slightly rearward of the axles — a little, and carefully, because too little tongue weight causes sway.
2. Over on GVWR? That is a mass problem, and only removing weight fixes it. Passengers, cargo, water. Fresh water is 8.34 lb per gallon and travelling with an empty tank is the single easiest large saving on most travel trailers.
3. Over on GCWR? The combination is too heavy for the drivetrain rating. Lighten either end, or you need a different truck.
4. Over on the front axle? Unusual when towing, and normally means the WD bars are over-tensioned. Back them off and re-measure.

Then re-weigh after the change. The whole value of the exercise is that you stop guessing.

How often

Once properly, with the rig loaded as you tow it. Then again whenever something material changes: a different trailer, a new toolbox or fifth-wheel rails, a bed camper, a habit of travelling with full tanks. Regular towers often weigh at the start of each season.

A ticket costs about the price of lunch. Set against the cost of a rear axle over its rating on a mountain descent, it is not a close decision.