Weight Distribution, Loading, and Axle Limits
Weight Distribution, Loading, and Axle Limits
Weight rules govern legality and control. The exam tests gross weight, axle limits, bridge formula, and load placement. In Pennsylvania, the general maximum gross weight is 80,000 pounds; single axles are typically limited to 20,000 pounds and tandem axles to 34,000 pounds, with the federal bridge formula controlling closely spaced axles. Always verify the current Pennsylvania Vehicle Code and permit conditions.
Core rules
- Never exceed tire load ratings or axle ratings.
- Keep enough weight on the steering axle for control; too little weight causes poor steering.
- Distribute load evenly; a heavy rearward load can unload the steering axle.
- Use a scale ticket to confirm axle weights, not an estimate.
- Check the bridge formula for short-wheelbase combinations.
Worked example
A tractor has a 12,000-pound steering axle, 32,000-pound drive tandem, and a trailer tandem at 32,000 pounds. Gross is 76,000 pounds, under 80,000. But if the trailer tandem is loaded to 36,000, the gross becomes 80,000 and the tandem exceeds 34,000, so the load is illegal. The fix is to shift freight forward or remove weight, then reweigh.
Traps
- Assuming gross weight under 80,000 means legal; axle limits can still be violated.
- Overloading the rear trailer and lightening the steering axle.
- Forgetting the dolly axle weight in a triple.
- Relying on a shipper's weight ticket without scaling.