CAT Scale Trailer Tongue Weight & WDH Load Restoral Calculator
Calculate exact trailer tongue weight, gross trailer weight, and SAE J2807 Front Axle Load Restoral (FALR) from CAT Scale 2-pass and 3-pass tickets. Includes sway risk meter and payload checks.
| Scale Platform Pad | Pass 1: With WDH | Pass 2: On Ball (No Bars) | Pass 3: Truck Alone | WDH Net Shift |
|---|---|---|---|---|
| Pad 1: Steer Axle (Front) | 3,220 lbs | 2,980 lbs | 3,380 lbs | +240 lbs |
| Pad 2: Drive Axle (Rear) | 3,740 lbs | 4,120 lbs | 2,680 lbs | -380 lbs |
| Pad 3: Trailer Axles | 6,300 lbs | 6,160 lbs | 0 lbs (Unhooked) | +140 lbs |
| Total Combined Rig Weight (GCW) | 13,260 lbs | 13,260 lbs | 6,060 lbs | Net Shifted: 380 lbs |
| Manufacturer Rating | Vehicle Limit | Scale Weight | Capacity Used | Checklist Result |
|---|---|---|---|---|
| Truck Gross Weight (GVWR) | 7,050 lbs | 6,960 lbs | 98.7% | Within Limit (+90 lbs) |
| Rear Axle Weight (Drive GAWR) | 4,150 lbs | 3,740 lbs | 90.1% | Within Limit (+410 lbs) |
| Front Axle Weight (Steer GAWR) | 3,525 lbs | 3,220 lbs | 91.3% | Within Limit (+305 lbs) |
| Receiver Hitch Tongue Limit | 1,100 lbs | 1,040 lbs | 94.5% | Within Limit (+60 lbs) |
| Gross Combined Weight (GCWR) | 16,200 lbs | 13,260 lbs | 81.9% | Within Limit (+2,940 lbs) |
How to Calculate Trailer Tongue Weight & WDH Load Restoral from CAT Scale Tickets
When towing a travel trailer, camper, boat, or cargo trailer, measuring actual tongue weight under full travel load is critical for preventing fatal highway trailer sway (fishtailing) and severe tow vehicle suspension damage. A commercial CAT Scale (Certified Automated Truck scale) uses three independent ground platform pads: Platform 1 measures the tow vehicle Steer Axle, Platform 2 measures the Drive Axle, and Platform 3 measures the Trailer Axles. Because the trailer tongue presses down behind the tow vehicle’s rear axle, it functions as a lever—lifting weight off the front steer tires while overloading the rear drive tires. By comparing a baseline pass of the truck alone against passes with the trailer hooked up (both with and without Weight Distribution Hitch spring bars tensioned), this calculator solves exact tongue weight, gross trailer weight, tongue weight ratio (10%–15% safety window), and SAE J2807 Front Axle Load Restoral (FALR).
Key Technical Specifications:
- Multi-Pass CAT Scale Ticket Math: Compares Steer, Drive, and Trailer axle weights across 2 or 3 separate scale tickets to isolate true tongue weight without disconnecting in traffic.
- SAE J2807 FALR Standard: Evaluates Front Axle Load Restoral percentage to verify that your Weight Distribution Hitch restores between 50% and 100% of unloaded front steer axle weight, ensuring proper steering and emergency braking control.
- 10%–15% Bumper-Pull Stability Index: Automatically audits your tongue weight ratio against NHTSA and RVIA dynamics rules to prevent low-tongue aerodynamic fishtailing (< 10%) or excessive nose sag (> 15%).
- Manufacturer Rating Compliance Audit: Compares real-world scale weights directly against your vehicle’s B-pillar door jamb ratings—Truck GVWR, Front GAWR, Rear GAWR, Hitch Tongue Limit, and GCWR.
- DIY 2×4 Lever Beam Solver: Includes mechanical torque equilibrium formulas for measuring lighter utility and boat trailers at home using a standard 300 lb bathroom scale.
The Step-by-Step Guide to Weighing Your Rig on a CAT Scale
1. Prepare Rig in Full Travel Configuration
Pack your tow vehicle and trailer exactly as you would for an extended road trip: fill fresh water tanks to typical travel levels, load passengers, propane tanks, luggage, firewood, and coolers.
2. Pass 1: Truck + Trailer WITH Weight Distribution Bars Attached
Pull onto the CAT scale with your Weight Distribution Hitch (WDH) fully tensioned in travel position. Ensure Steer axle is on Pad 1, Drive axle is on Pad 2, and all trailer tires are on Pad 3. Use the Weigh My Truck app to record ticket #1.
3. Pass 2: Truck + Trailer on Ball WITHOUT WDH Tension
Pull off into the truck stop parking lot, disconnect or unpin the WDH spring bars/chains, and drive back onto the scale with the trailer resting directly on the ball. Record ticket #2 (re-weigh).
4. Pass 3: Tow Vehicle Alone (Baseline)
Drop the trailer in a designated parking stall, drive only your truck back onto the scale with front wheels on Pad 1 and rear wheels on Pad 2. Record ticket #3.
5. Input Scale Ticket Numbers into Calculator
Enter the three sets of Steer, Drive, and Trailer weights. The calculator automatically computes your exact Tongue Weight, Sway Risk Index, FALR Restoral %, and Door Jamb payload margins.
6. Adjust Spring Bar Tension & Cargo Positioning
If tongue weight is below 10%, shift heavy cargo forward in the trailer. If FALR is under 50%, tighten your WDH spring bar chains by 1 link or tilt the hitch head back 1 notch.
Top Troubleshooting Pitfalls & Solutions
Common Questions on CAT Scale Trailer Tongue Weight & WDH Restoral Calculator
What is the ideal tongue weight percentage for a bumper-pull travel trailer?
The ideal tongue weight for standard bumper-pull travel trailers is between 10.0% and 15.0% of total loaded trailer weight (Gross Trailer Weight), with 12.0%–13.0% considered the industry sweet spot. Fifth-wheel trailers require 15%–25% pin weight.
How do I calculate tongue weight using a CAT Scale?
Take two scale passes: Pass 1 with your truck and trailer fully hooked up, and Pass 2 with your truck alone. Add Steer Axle + Drive Axle weights on Pass 1 (loaded truck), then subtract Steer Axle + Drive Axle weights on Pass 2 (truck alone). The difference is your exact tongue weight.
What is SAE J2807 Front Axle Load Restoral (FALR)?
SAE J2807 is the automotive engineering standard governing vehicle tow ratings. When a trailer sits on the hitch ball, it lifts weight off the front steer axle. FALR measures the percentage of that lost front-axle weight restored by your Weight Distribution Hitch. Modern truck manufacturers (Ford, GM, Ram, Toyota) recommend 50% to 100% FALR.
Why does my truck squat even with a Weight Distribution Hitch installed?
Some rear suspension squat (1 to 2 inches) is completely normal and designed into leaf springs. However, if your front steer axle is higher than unhitched baseline, your WDH spring bars are under-tensioned (under 50% FALR). Tightening the bars will level the truck and restore front steering bite.
Does tongue weight count against my vehicle’s payload capacity?
Yes. 100% of the trailer tongue weight presses directly onto the receiver hitch, counting as payload against your vehicle’s Gross Vehicle Weight Rating (GVWR). You must account for tongue weight, passengers, hitch hardware (80–120 lbs), and truck bed cargo.
Can I weigh my tongue weight at home with a bathroom scale?
Yes, for trailers with tongue weights under ~600 lbs. Using a 3-foot 2×4 board with a pipe pivot, placing the trailer jack 1 foot from the pivot and the bathroom scale 3 feet from the pivot creates a 3:1 mechanical advantage. Multiply the scale reading by 3 to find total tongue weight.