Overweight Steer Axle, Forty-Two Feet of Lumber, and a Box of Chains
You are at a shipper's dock in Catoosa, Oklahoma, with a 3-axle tractor and a 53-foot flatbed with sliding tandem axles. The load is 42-foot-long bundles of treated lumber, 30,000 pounds total in six banded bundles. The dock hand offers 5/16-inch grade-70 chains with lever binders, plus some 4-inch nylon straps marked at 5,400 pounds working load limit. The yard scale ticket reads: steer axle 12,300 lb; drive tandems 33,900 lb; trailer tandems 32,000 lb. The steer axle is rated at 12,000 lb, the drive and trailer tire groups are rated at 34,000 lb each, and the gross limit is 80,000 lb. The trailer's tandems are in the middle of their slide range and the fifth wheel is in its forward position. You have six chains available.
1. Is the lumber legally secured with six chains? Walk through the tiedown count and the aggregate working load limit.
Read the worked answer
Count: the cargo is one article over 5 feet long and well over 1,100 pounds, so it needs at least two tiedowns, plus one more for each additional 10 feet of length beyond the first 10. Forty-two feet means 2 tiedowns for the base plus 4 more for the length - a minimum of 6. Each bundle also has to be individually restrained; a single chain thrown over the whole stack does not secure the bundles to each other.
Aggregate working load limit: for cargo that is not blocked against a front-end structure, the combined WLL of the tiedowns must be at least half the cargo weight. Half of 30,000 is 15,000 lb. Six 5/16 grade-70 chains at 4,700 lb WLL each give 28,200 lb - comfortably over.
But the count is not the whole answer. The lever binders must have their handles secured so they cannot open, the chains must be free of kinks, cracks, and stretched links, the binders' WLL counts too, and the chains must be attached to the trailer's tiedown anchors rather than to the rub rail or a stake pocket not rated for it. The front of the load needs to bear against the headboard or be secured against forward movement, and the lumber needs edge protection where chains cross it.
Conclusion: six chains satisfy the count and the WLL, provided the hardware and attachment points check out.
2. Which axle is illegal, and in what order do you make adjustments? Show the arithmetic.
Read the worked answer
Current readings: steer 12,300 against a 12,000 rating - 300 lb over. Drives 33,900 against 34,000 - only 100 lb of headroom. Trailer tandems 32,000 against 34,000 - 2,000 lb of headroom. Gross 78,200 against 80,000 - legal.
The obvious move is to slide the fifth wheel rearward, since that shifts weight off the steer and onto the drives. But the drives have only 100 lb of room, so sliding the fifth wheel first would put the drives over the limit and you would be chasing the problem around the truck.
Correct order:
- Slide the trailer tandems rearward two positions. That transfers roughly 300 lb per position off the drives and onto the trailer axles: drives about 33,300, tandems about 32,600.
- Slide the fifth wheel rearward two holes. That shifts roughly 250 lb per hole off the steer: steer about 11,800, drives back up to about 33,800.
- Re-weigh. These per-hole figures are estimates; the real transfer depends on the load's center of gravity and the trailer's axle spread, so the scale decides, not the arithmetic.
Watch the trailer's rear overhang and tail swing after moving the fifth wheel back, and confirm the trailer nose still clears the cab.
3. Could the nylon straps be used instead of chains? What has to be true?
Read the worked answer
Yes, if the numbers and the condition work.
Numbers: six straps at 5,400 lb WLL each gives 32,400 lb aggregate, which clears the 15,000 lb requirement, and six straps meet the tiedown count for 42 feet. Even four would clear the WLL requirement mathematically, but the count rule still demands six for that length, so you cannot trade count for strength.
What has to be true: every strap must be marked with its rating (unmarked webbing is treated as unusable), free of cuts, burns, UV damage, and knots, and fitted with a working ratchet or winch. Rough-sawn treated lumber will abrade and cut webbing, so edge protectors or corner boards are not optional - a strap that frays through in the first hundred miles is worse than a chain because the failure is silent. The anchor points must be rated and the hooks must be closed.
Practical call: chains with lever binders are the better choice for heavy lumber because they resist abrasion and cutting, and the binders can be checked at a glance by confirming the handles are secured. If you do use straps, expect to stop and re-check tension after the first 50 miles, and check them again at every stop. Straps stretch and lumber settles.