Cantilever Slide Gate Roller and Track Sizing
Why this matters
A cantilever slide gate carries its own weight on rollers riding inside an inverted track welded to the gate frame, supported on truck assemblies bolted to posts on one side of the opening only. There are no rollers in the driveway. Sizing the rollers, the track, and the support trucks is a load and lever calculation; get it wrong and the gate sags into the driveway, the rollers spall, or the trucks bend the posts. Get it right and the gate runs for decades. ASTM F2200 governs the construction of the gate; UL 325 governs the automated operator on the gate. Both standards reference roller and track ratings indirectly through the structural-integrity requirement.
What ASTM F2200 actually requires
ASTM F2200, "Standard Specification for Automated Vehicular Gate Construction," requires the gate to be constructed so that all structural components are sized and connected to support the gate's weight, dynamic loading from operation, and any expected entrapment loads. The standard does not publish roller sizes directly; it requires the designer (gate fabricator or installer) to size components to support the loads with a documented engineering basis. Manufacturer published load ratings on rollers and track satisfy this requirement when the gate weight and lever arm are within the manufacturer's tested envelope.
UL 325, "Safety of Door, Drapery, Gate, Louver, and Window Operators and Systems," covers the powered operator (the motor and controls), entrapment protection, and the related sensors. UL 325 does not specify roller or track sizing but requires the gate plus operator system to function safely; an undersized roller failing during operation creates a UL 325 entrapment risk.
Gate weight is the first number
Cantilever slide gates are aluminum, galvanized steel, or stainless steel framework filled with picket, chain link, ornamental, or solid panel infill. Typical weights:
- Aluminum cantilever gate, ornamental picket, 20 ft opening: 200 to 350 lb.
- Galvanized steel cantilever gate, chain-link infill, 20 ft opening: 350 to 550 lb.
- Steel cantilever gate, solid panel infill (privacy), 20 ft opening: 600 to 1,000 lb.
- Steel cantilever gate, 30 to 40 ft opening, heavy industrial: 800 to 2,000 lb.
The gate frame extends past the opening on the carrier side by a cantilever length equal to typically 40 to 50 percent of the clear opening. A 20 ft opening gate has a 28 to 30 ft total length; the extra 8 to 10 ft is the counterbalance length that lives behind the posts when the gate is open.
Truck spacing and post lever arm
The gate runs on two truck assemblies bolted to two posts on the carrier side. Truck spacing equals one-third to one-half of the total gate length per the major manufacturers (DAC, ALEKO, Hoover Fence, Mighty Mule, Master Halco). For a 28 ft gate, truck spacing of 10 to 14 ft is typical. Closer spacing reduces the lever arm and the post moment but uses gate-end-bearing area inefficiently.
Each post carries vertical load (the gate weight share at that post, which is uneven because of the cantilever) and lateral load (the gate trying to twist out of the track from wind and operation). Post sizing typical:
- Schedule 40 steel post, 4 inch nominal diameter, 1/4 inch wall, 7 to 9 ft above grade, in a concrete footing 24 to 36 inches diameter by 36 to 48 inches deep: handles up to roughly 500 lb gate weight in moderate wind exposure.
- Schedule 40 steel post, 6 inch nominal diameter, 1/4 inch wall, in a 36 to 42 inch diameter footing by 48 inches deep: handles 500 to 1,000 lb gate weight.
- Heavy industrial gates over 1,000 lb often require structural-grade I-beam or HSS rectangular posts in deeper footings; engineer involvement is the norm at that scale.
Post embedment depth needs to clear local frost line per IRC R403; verify the AHJ before pouring.
Roller (truck) load ratings
Cantilever gate trucks are roller assemblies with a number of small wheels (typically 4, 6, or 8) riding inside the inverted track. Manufacturers publish load capacity ratings per truck:
- Small residential trucks (DAC 580 series and equivalent): 400 to 600 lb per truck pair.
- Medium duty trucks (DAC 680 series and equivalent): 600 to 1,200 lb per truck pair.
- Heavy industrial trucks (DAC 880 series, Hoover Fence heavy): 1,200 to 3,000 lb per truck pair.
A correctly designed gate keeps the worst-case single-truck load below 70 percent of the published rating to allow for dynamic operation and wind. For a 500 lb gate on two trucks the calculation accounts for the cantilever distribution: the front truck (closer to the opening) carries more than half the weight because of the counterbalance lever, often 60 to 70 percent of the gate weight on the front truck.
Track size matched to truck
Manufacturer track is paired with truck size: small trucks use 1 to 1-1/4 inch nominal aluminum or steel track; medium-duty trucks use 1-5/8 to 2 inch track; heavy industrial trucks use 2-1/2 to 3 inch structural steel track. The track ID dimension must match the truck OD dimension within manufacturer tolerance; a track too loose lets the wheels chatter and skip, a track too tight binds.
Track material: extruded aluminum (lighter, lower cost, good for aluminum gates), galvanized steel, stainless steel for corrosive environments (coastal, industrial chemical). Track length equals total gate length plus 6 to 12 inches of run-out at each end so the trucks have a relief beyond the working span. The track is welded to the gate frame with continuous fillet welds per the manufacturer's detail.
Wheel and bearing maintenance
Truck wheels run on sealed precision ball bearings. Standard maintenance: visual inspection at every operator service, lubrication of any unsealed pivot points per the manufacturer (most modern truck designs are sealed and require no lubrication). Replace any wheel showing flat-spotting, bearing roughness, or audible roar; a failing wheel transfers load to neighboring wheels and accelerates the failure across the truck.
Wind load adders
Solid-panel cantilever gates in high-wind exposure (coastal, mountain ridge) need wind-load analysis per ASCE 7. A 24 ft by 6 ft solid panel gate in a 110 mph wind zone (common Florida and Gulf coast) can see 2,000-plus pounds of lateral load; this drives up post, truck, and footing sizing significantly compared to an open-picket gate.
Per ASTM F2200, vehicular gates must not have any opening through which a 2-1/4 inch diameter sphere can pass anywhere up to 48 inches above grade in the swept path of the gate. Cantilever gates that run between vertical bars or pickets routinely violate this rule and create entrapment hazards. Verify the design before fabrication; standard wide-picket designs may need additional mesh or panel infill in the lower 48 inches.
References
- ASTM F2200, "Standard Specification for Automated Vehicular Gate Construction."
- UL 325, "Safety of Door, Drapery, Gate, Louver, and Window Operators and Systems."
- ASCE 7-22, "Minimum Design Loads and Associated Criteria for Buildings and Other Structures," wind load chapters.
- IRC R403, footing depth and embedment minimums.
- Manufacturer technical specifications for DAC Industries, Hoover Fence, ALEKO, and Master Halco cantilever gate hardware including published truck load ratings.