A fifth-wheel slide calculator tells a driver how many holes to slide the fifth wheel or trailer tandems to redistribute axle weight and stay under federal limits. US federal limits are 12,000 lb on the steer axle, 34,000 lb on the drive tandem, and 34,000 lb on the trailer tandem (80,000 lb gross). Canadian federal limits are 5,500 kg / 18,000 kg / 17,000 kg respectively. TruckerPro's free axle weight calculator does the rebalance math from your scale ticket.
TL;DR
- US federal limits: steer 12,000 lb / drive tandem 34,000 lb / trailer tandem 34,000 lb / gross 80,000 lb.
- Canada federal limits: steer 5,500 kg / drive tandem 18,000 kg / trailer tandem 17,000 kg.
- One hole of slide ≈ 250–500 lb shift between the relevant axle groups.
- Slide trailer tandems forward to shift weight off the drives onto the trailer; slide back to shift weight off the trailer onto the drives.
- Free calculator at
/tools/slide-calculatorreturns hole counts and direction from current scale weights.
What is fifth-wheel slide and why does it matter?
The fifth wheel is the coupling plate mounted on the rear of the tractor frame that connects to the trailer kingpin. On modern tractors it sits on rails that allow it to slide fore and aft — typically with 1-inch hole spacing on a 12-inch (or larger) rail.
Sliding the fifth wheel changes where on the tractor the trailer's load is bearing. Slide forward, more weight rests on the steer axle. Slide back, more weight transfers to the drive tandems. It's one of two adjustment levers drivers have for axle weight; the other is the trailer tandem slide.
Why it matters: a load that was loaded by the shipper without driver-side input may put 36,500 lb on the drive tandems — 2,500 lb over the federal limit. The driver hits the scale, sees the overweight, and has to fix it before continuing. The two options:
- Re-weigh the load distribution at origin. Often impossible — the shipper has moved on, the dock is closed, or you're hours down the road.
- Slide. Move the fifth wheel and/or trailer tandems to shift weight between axle groups until everything is under the limit.
For a driver who's caught the overweight at the cat scale before reaching a DOT inspection station, sliding is a 5–10 minute fix that avoids a scale-house ticket. For a driver who skipped the cat scale and rolled up to a DOT station, sliding is the same fix but now happens under inspector supervision.
How much weight does one slide hole shift?
Approximate — and emphasize approximate — weight transfer per hole:
- Trailer tandem slide: one hole (typically 6 inches) shifts roughly 250–500 lb between the drive tandem group and the trailer tandem group.
- Fifth-wheel slide: one hole (typically 4 inches) shifts roughly 250–500 lb between the steer axle and the drive tandem group.
The actual shift depends on the load distribution inside the trailer. A load with weight concentrated near the front bulkhead transfers more per hole than a load distributed evenly along the trailer floor. A load with weight concentrated near the rear transfers less.
The practical rule: always reweigh after sliding. Don't assume the math is exact. A driver who slides 3 holes expecting a 1,200 lb shift may actually get 900 or 1,500 — both possible, both common. Re-cross the cat scale, re-read the ticket, slide again if needed.
What are the federal axle weight limits?
The headline numbers, US and Canada:
| Axle group | US Federal (lb) | Canada Federal (kg) | Canada Federal (lb equiv) |
|---|---|---|---|
| Steer axle | 12,000 | 5,500 | 12,125 |
| Drive tandem (dual axle) | 34,000 | 18,000 | 39,683 |
| Trailer tandem (dual axle) | 34,000 | 17,000 | 37,479 |
| Drive tridem (triple axle) | n/a — non-standard | 24,000 | 52,910 |
| Trailer tridem (triple axle) | n/a — non-standard | 21,000 | 46,297 |
| Gross combination weight | 80,000 | 39,500 (5-axle) / 53,500 (8-axle B-train) | varies |
A few critical caveats:
- US state variations. Federal limits are the floor for federal-aid highways. States can run higher on non-federal-aid roads or under specific permits. California's Bridge formula and Michigan's 11-axle configurations are notable exceptions.
- Canadian provincial variations. SPIF (Safe, Productive, Infrastructure-Friendly) configurations in Ontario allow higher weights for compliant equipment. Quebec's Loi sur les véhicules routiers and BC's CVSE have provincial variations. The federal numbers are the National Safety Code (NSC) baseline; provincial road authorities apply their own limits.
- Bridge formula. Both jurisdictions apply a "bridge formula" that limits gross weight as a function of axle spacing — closer-together axles are limited to lower combined weight than spread axles. This is why a 5-axle 80,000 lb limit applies to typical tractor-trailers but a 4-axle straight truck is much more constrained.
- Permit moves. Heavy haul, oversize, and specialized loads operate under permits with explicit higher limits — but those are per-trip, route-specific, and require driver attention to permit conditions.
For day-to-day OTR dry van and reefer drivers, the headline numbers above are what matter. Memorize the steer/drives/trailer trio.
How to use the slide calculator: a worked example
Scenario: driver's first scale ticket reads:
- Steer: 11,400 lb (under 12,000 limit, OK)
- Drives: 36,200 lb (over 34,000 — 2,200 lb over)
- Trailer: 30,800 lb (under 34,000, OK)
- Gross: 78,400 lb (under 80,000, OK)
The drives are 2,200 lb over. The driver needs to shift weight off the drives onto the trailer. That means sliding the trailer tandems forward (toward the front of the trailer) — moving the trailer axles forward shifts weight onto the trailer wheels and off the drive wheels.
Estimated holes needed: 2,200 lb ÷ ~400 lb per hole = 5–6 holes forward.
Walk through it:
- Pull off the scale to a flat staging area.
- Apply trailer brakes, release the trailer slide pin, count out 5 holes forward, re-engage the pin, release brakes.
- Re-cross the cat scale. Expected reading: drives ~34,200 lb, trailer ~32,800 lb.
- If still over, slide one more hole. If now under by a comfortable margin, depart.
The free axle weight calculator does this math automatically — input current scale weights and target limits, get the hole count and direction. Useful for drivers new to load distribution math; useful even for experienced drivers as a sanity check before sliding.
What happens at the scale if I'm overweight?
Two scenarios with very different outcomes.
Scenario A: Caught at a private cat scale before a DOT inspection. No ticket, no consequence. The driver pays $13–$15 for the weighing, slides, re-weighs, and proceeds. This is what cat scales are for — running them is cheap insurance.
Scenario B: Caught at a DOT or Transport Canada scale-house inspection. Possible consequences:
- Citation/ticket — varies by jurisdiction and overage. US fines typically run $50–$500 for the first 1,000 lb overweight, escalating sharply (up to several thousand dollars) for larger overages. Canadian provincial fines are similar in magnitude.
- Out-of-service order — the truck cannot move until weight is redistributed. The driver fixes it on-site, in the inspection lot, while the inspector watches.
- CSA score impact (US) — overweight violations contribute to the carrier's Vehicle Maintenance and Driver Fitness BASIC scores. Repeat offenses signal poor pre-trip discipline and can trigger inspections at future stops.
- Insurance premium impact — carriers with poor CSA scores see commercial auto insurance premiums climb at renewal. The carrier eats the cost of the driver's overweight tickets.
- Driver-side consequences — depending on the carrier's policy, the driver may pay the ticket personally, be put on a coaching plan, or lose the route assignment.
The pragmatic rule: always cross a cat scale on the way out of the shipper if there's any uncertainty about load distribution. $14 at a cat scale is cheaper than the lowest possible scale-house ticket, every time.
When should I slide forward vs back?
Trailer tandem direction logic:
- Drives over, trailer under → slide trailer tandems forward. Moves weight onto the trailer.
- Drives under, trailer over → slide trailer tandems back. Moves weight onto the drives.
Fifth-wheel direction logic:
- Steer over, drives under → slide fifth wheel back. Moves weight onto the drives.
- Steer under, drives over → slide fifth wheel forward. Moves weight onto the steers.
If multiple groups are over, the driver may need to slide both. Common case: drives 2,000 lb over, steer 800 lb under, trailer 1,200 lb under. Slide trailer tandems forward 4–5 holes (drives → trailer), then if needed slide fifth wheel forward 1–2 holes (drives → steer).
A clean pre-trip habit: cross a cat scale every time after a loaded pickup. Doing it once a day on every loaded leg builds the muscle memory; doing it occasionally creates the failure mode of skipping it on the load that actually needed it.
For drivers running cross-border freight, also confirm both US and Canadian limits — a load legal in one jurisdiction may be illegal in the other. Pair this with a pre-trip inspection checklist and the broader DOT inspection checklist for the full pre-departure routine.
How does TruckerPro's free axle weight calculator work?
The free slide calculator takes inputs from your scale ticket:
- Steer axle weight
- Drive tandem weight
- Trailer tandem weight
- Jurisdiction (US federal, US state, or Canada federal/provincial)
It returns:
- Which axle groups are over (and by how much)
- Which axle groups are under (and by how much)
- Direction and hole count for trailer tandem slide
- Direction and hole count for fifth-wheel slide
- Predicted post-slide weights
The tool is free, browser-based, and works offline once loaded — useful for drivers in dead-zone scale-house lots. Run it on the cab phone or tablet during the cross-the-scale → re-weigh cycle.
A note on accuracy: like all slide math, the calculator's predictions are approximate (typical 250–500 lb per hole, varies by load distribution). Always re-weigh after sliding to confirm. The calculator gets you to the right ballpark; the cat scale ticket confirms the exact result.
Frequently Asked Questions
What is fifth-wheel slide?
The fifth wheel is the coupling on a tractor that connects to the trailer kingpin. On most modern tractors it slides forward and back on rails — usually with 1-inch hole spacing — to shift weight between the steer axle and the drive tandems. It is one of two ways drivers rebalance an overweight axle group, the other being trailer tandem slide.
How much weight does one slide hole shift?
Sliding the trailer tandems one hole (typically 6 inches) shifts roughly 250–500 lb between the drive tandem and the trailer tandem, depending on the load distribution. Sliding the fifth wheel one hole shifts a similar amount between the steer axle and the drive tandems. Always reweigh after sliding — the math is approximate.
What are the federal axle weight limits in the US and Canada?
US federal limits: steer 12,000 lb, drive tandem 34,000 lb, trailer tandem 34,000 lb, gross 80,000 lb (state-by-state variations exist). Canadian federal limits in kilograms: steer 5,500 kg, drive tandem 18,000 kg, trailer tandem 17,000 kg, with provincial variations under SPIF and other configurations. Always check the jurisdiction-specific bridge formula for your route.
What happens at the scale if I'm overweight?
DOT and Transport Canada inspectors can issue a ticket on the spot, place the truck out of service until the driver redistributes weight, and require reweighing before continuing. Tickets can run from a few hundred to several thousand dollars depending on the overage and jurisdiction. Repeat offenses raise CSA scores and insurance premiums.
When should I slide the trailer tandems forward vs back?
Slide trailer tandems forward to shift weight onto the trailer and off the drives. Slide them back to take weight off the trailer and put it onto the drives. The same logic applies in reverse for the fifth wheel — sliding it back puts weight onto the drives, sliding it forward puts weight onto the steers.
How does the free axle weight calculator help?
Enter your current scale-ticket weights (steer, drives, trailer) and the legal limits. The calculator tells you how many holes to slide in which direction to bring all axle groups under the limit before you re-scale. It saves a second trip to the cat scale and a possible scale-house ticket.