Cast Iron Caster Load Capacity by Wheel Diameter and Tread Width: How to Read a Per-Wheel Rating and Compare Suppliers

Firs check what the rating number actually describes

Before you compare any two figures, establish what each one covers. Load capacity is set by the whole caster assembly — wheel, axle, fork, swivel section, mounting method and floor condition — so a bare-wheel figure and an assembled-caster figure are not interchangeable²⁰.

On single-wheel casters the wheel and caster ratings are the same. On dual-wheel casters, where two wheels share an axle, capacity per caster is usually 1.5-2x the per-wheel figure because both wheels share the load¹¹.

Ask which of those two numbers a catalogue is listing before you use i The worked case shows how much the basis matters. A 6 x 2 in cast iron wheel with roller bearing is listed at 1,500 lb as a wheel only⁴.

The same size and bearing on a kingpinless rigid caster is rated 1,400 lb, with the series rated to 2,000 lb/ea¹³. Neither listing states whether its figure is static or dynamic, so treat the two as different scopes rather than a contradiction to resolve.

For your own selection, the practical rule is to treat any figure that does not name its basis as unusable until the supplier confirms i Ask whether the number is per wheel or per caster, and whether it is static or dynamic.

Match diameter and tread width to your load class, then get the figure from the manufacturer

Diameter and tread width are the two variables you specified, and the sources agree on their direction but not their arithmetic. Larger diameter wheels roll more easily, handle obstacles better and distribute weight more effectively^16,24.

Wider treads spread load over a larger contact area and are selected for heavy loads on uneven floors^16,25. Neither relationship comes with a number you can multiply by.

What exists instead is screening guidance by load class, and it is general caster guidance rather than cast-iron-specific. The bands are 3-5 in for light load, 4-6 in for medium load and 6-12 in for heavy load².

Cast iron and steel wheels sit in the 1000 kg and above per-caster band, with floor protection and noise as the checks before specifying¹⁷. Use those bands to confirm your chosen diameter is in the right class, not to derive a capacity.

For the capacity itself, the range is wide. Cast iron replacement wheels are available with ratings up to 40,000 lb per wheel in the largest diameters, with standard industrial sizes commonly 1,000 to 15,000 lb per wheel⁴.

That spread is exactly why a diameter-and-width table matters: your 6 x 2 in size sits far below the ceiling, and only the manufacturer's own table tells you where in the range it falls. Request that table by diameter and tread width from each supplier you are considering.

Choose the bearing and axle, knowing the bearing raises capacity but does not set the rating

Roller bearings generally have a higher load-bearing capacity than ball bearings because they distribute load over a larger surface area¹⁸. For heavy loads, roller bearings or 6204 ball bearings are preferred, with load capacity more than 30% above ordinary bearings².

That makes roller the sensible default for a cast iron wheel in heavy industrial duty. Do not read that as the bearing setting your rating.

The bearing can support smoother wheel rotation under load, but load capacity is determined by the whole caster assembly — wheel, axle, fork, swivel section, mounting method and floor condition²⁰. The bearing is one element in the chain, not the chain.

The worked case shows the supporting hardware that comes with a heavy cast iron wheel: a 6 x 2 in cast iron wheel with roller bearing, Brinell 145 hardness and a 1/2 in axle, on a kingpinless rigid caster¹³.

When you specify, give the supplier the bore and axle size you need and ask what load and speed limit they attach to that bearing and bore combination. No source in this set publishes one.

Set the per-caster load you will actually specify

The catalogue figure is a ceiling, not a targe Sources converge on a margin above calculated static load.

But they do not agree on its size: at least 20% above calculated load¹¹, a safety factor of 1.5 or more², 20-30% above the calculated minimum²³, or dividing gross weight by the number of wheels minus one and then buying 20% above that¹⁷.

Treat these as screening values from the cited sources rather than a governing standard, and pick the one your duty cycle justifies. Dynamic duty adds margin on top.

Dynamic load per caster can be calculated as static load times an acceleration factor of 1.1-1.3, an uneven-distribution factor of 1.1-1.5, and an environmental factor greater than 1 on rough, hot or corrosive surfaces¹⁸.

Sudden starts and stops drive the acceleration factor, uneven load distribution drives the distribution factor, and rough or uneven floors, high temperature or corrosive environments drive the environmental factor above 1¹⁸. Where impacts at thresholds are frequen uprating capacity and using sealed bearings is the recommended response²⁵.

Work the arithmetic on your own cart before you quote. Take the loaded weigh divide by the number of casters you intend to load, apply your chosen margin, then apply the dynamic factors that match your route.

The result is the per-caster number you put in the RFQ — not the catalogue figure.

Confirm the mounting configuration before you release the RFQ

Mounting method is one of the assembly elements that determines capacity, so a rig change is a rating change, not just a fitting change²⁰. Check these against the cart's existing frame before you send the enquiry.

• ✓Confirm the top plate size and bolt-hole pattern match your frame — one cast iron caster lists a 4 x 4-1/2 in top plate with a 2-5/8 x 3-3/8 in pattern slotted to 3 x 3 in.
• ✓Confirm the recommended plate bolt size, listed as 3/8 in on that caster.
• ✓Confirm the axle size and bore match your wheel and rig, listed as 1/2 in diameter with a zerk fitting on that caster.
• ✓Confirm the mounting height clears your frame, listed as 7.5 in on that caster.
• ✓Ask the supplier to confirm the rated capacity applies to the mounting configuration you are ordering, since the assembly as a whole sets capacity.

Decide whether cast iron is acceptable on your floor and duty cycle

Cast iron is a hard, non-resilient tread, and that has consequences beyond load. Cast iron wheels will gradually wear, crack and damage concrete floors under extreme loads, especially during turns and over floor joints⁴.

In foundries and heavy manufacturing that wear is generally accepted as part of the operating environmen for floor-sensitive areas, polyurethane-on-iron wheels add a protective tread layer⁴. Noise is the second check.

Cast iron and steel wheels carry floor protection and noise as the two items to confirm before specifying¹⁷. If your cart runs through occupied areas or over finished floors, weigh that against the load class you need before you compare prices.

If your route is floor-sensitive, the material decision comes before the commercial one. Polyurethane-on-iron keeps an iron core carrying the load with a tread layer between wheel and floor⁴.

Settle that question firs because it changes which casters you are quoting.

Normalise quotes onto the same basis before comparing price

Caster cost is driven by material, load capacity, wheel size and type, and bearing type, so two quotes that differ on any of these are not comparable^14,21.

A bare unit price for one rig and a bare unit price for another tell you nothing unless both quotes state the same load basis, wheel and bearing²¹.

Ask each supplier to quote against the same load per wheel, duty cycle, wheel and bearing, and mounting configuration, and to state which cost drivers are included and which are excluded²¹.

Volume discount tiers are part of that picture: one caster in this source set is priced at $213-$235 with discounts of 5% at 50 units, 10% at 100 and 15% at 200²¹.

That is a single produc not a market benchmark, but it shows the shape of the structure you should ask both bidders to quote agains Two requests belong in the RFQ itself. Ask for the diameter x tread-width capacity table, since no source in this set publishes one.

Ask for the load condition behind each rating — static or dynamic — because no source states it either.

Where the sources disagree, and what to ask

Two figures a buyer is most likely to quote are the 6 x 2 in capacity and the safety margin, and the sources do not resolve either. Keep both positions visible and put the question to the supplier.

Before you request a quote

• Public sources do not settle this — put it to the supplier: no source provides a complete cast iron wheel load capacity table by diameter and tread width combination.
• Public sources do not settle this — put it to the supplier: no source states the load condition (static, dynamic or continuous) behind cast iron wheel capacity ratings.
• Public sources do not settle this — put it to the supplier: no source gives a capacity-per-inch-of-tread-width figure or a capacity-versus-diameter curve for cast iron wheels.
• Public sources do not settle this — put it to the supplier: no source states whether the cast iron capacity table is linear, stepped, or capped by bearing or axle limits.
• Public sources do not settle this — put it to the supplier: no source gives a numeric derating factor for the caster rig, axle, bearing or mounting configuration on a cast iron wheel.
• Public sources do not settle this — put it to the supplier: no source gives a numeric load or speed limit tied to a specific bearing type and bore size on a cast iron wheel.
• Public sources do not settle this — put it to the supplier: no source publishes a manufacturer or standards-body derating table specific to cast iron wheels for shock, impac uneven floors, temperature or continuous duty.
• Request the complete specification sheet with units, test conditions and configuration assumptions.
• Request a written quote with price basis, MOQ, tooling, payment terms and production lead time.
• Public sources do not settle this — put it to the supplier: no source provides a direct comparison of multiple manufacturers' cast iron wheel capacity tables at the same diameter and tread width.