Towball leverage
Uses towball weight, wheelbase and rear overhang to illustrate static leverage.
Why rear axle load can increase by more than the towball weight
The towball is normally positioned behind the rear axle. Its downward force therefore acts through the wheelbase as a lever. The further the towball sits behind the rear axle, the greater the estimated transfer away from the front axle.
The rear axle carries the towball load plus the amount transferred from the front axle. This is why a 300 kg towball load can add substantially more than 300 kg to the rear axle in a static calculation.
What this free calculation includes
Front axle unloading
Estimates how much load may be removed from the front axle.
Rear axle increase
Estimates towball load plus the load transferred from the front axle.
This page provides an illustrative static-leverage estimate. It does not confirm actual axle loads or legal compliance. Use measured geometry and loading information, compare results with the vehicle's supplied ratings, and obtain weighbridge or qualified professional verification where appropriate.
Rear axle load calculation: a transparent example
For a static example without a weight-distribution hitch, use 300 kg towball load, 3,000 mm wheelbase and 1,200 mm from rear axle centre to towball. Front-axle unloading is 300 × 1,200 ÷ 3,000 = 120 kg. Rear-axle increase is 300 + 120 = 420 kg. The total change on the vehicle remains 300 kg.
From axle change to total axle load
If the travel-ready uncoupled rear axle reads 1,600 kg, this example estimates 2,020 kg after coupling. Against an entered 2,100 kg rear-axle limit, only 80 kg of calculated headroom remains. Measure both axles in the coupled condition: geometry, starting weights and loading assumptions all affect the estimate.
Can this tool measure towball weight?
No. Enter a measured or clearly labelled estimated coupling load. Dividing measured towball mass by actual loaded caravan mass gives a percentage, but this does not determine an approved or stable loading range. Follow the caravan and vehicle manufacturer instructions; moving cargo merely to achieve a percentage can create other problems.
Does a weight-distribution hitch increase the ratings?
Do not assume it does. A weight-distribution hitch changes the load distribution and is outside this simple three-input model. Confirm compatibility and setup instructions with the vehicle and equipment manufacturers, and verify the relevant loaded axle readings.
When is the $29 calculator/report useful?
Use the Detailed Weight Distribution Calculator & Report when you want to model multiple load positions and review axle, GVM, GCM and towing calculations together. For a vehicle-and-caravan purchase decision, use the $99 Vehicle + Caravan Assessment.
Choose your next step
Free tools help you understand individual checks. Choose the report that matches the decision you need to make.
Australian reference guidance: Queensland towing weights and vehicle selection, towing equipment and road authority guidance by state. Examples above are illustrative calculations. Verify the exact ratings and loaded weights for your setup. See our editorial methodology.