Furniture Castors — Selection & Load Capacity

Furniture castors are mechanical components fitted beneath furniture or equipment to make them mobile; they vary primarily in their load capacity, wheel diameter, tread properties, and mounting method.

Choosing the exact right castor determines whether a heavy workshop trolley can be manoeuvred with precision or whether a living room cabinet scratches an expensive parquet floor. For joiners, fitters, and ambitious DIY enthusiasts, it is essential to understand the physical and mechanical properties of the various castor types. This guide breaks down the technical specifications and provides the calculation principles for correct dimensioning.

Types and Designs of Furniture Castors

The kinematics of mobile furniture are determined by the combination of castor types used. In practice, different types are usually fitted to a single unit to achieve a balance between directional stability and manoeuvrability.

Swivel Castors and Fixed Castors

The swivel castor features a vertical swivel bearing, often designed as a ball race. This allows the wheel to rotate 360° around its vertical axis. The furniture item can be manoeuvred in any direction. The fork of the castor has a defined offset – the wheel trails behind the swivel axis, which makes precise alignment easier when pushing.

The fixed castor, on the other hand, is rigidly mounted. It only permits linear forward and backward movement. Combining two swivel castors (usually on the pushing side) with two fixed castors is standard for transport trolleys. This ensures the unit tracks straight over long distances while remaining easy to steer around corners. If four swivel castors are used instead, the furniture can rotate on the spot and move sideways, but it can easily veer off track when pushed over longer distances.

Castors with Brakes

To prevent accidental rolling, swivel castors are frequently equipped with a brake. Technically, a distinction is made between two variants:

• Wheel brake: Locks only the rotation of the wheel. The fork can still rotate around its vertical axis.
• Total brake: Locks both the rolling wheel and the swivel race of the fork when the foot lever is pressed. The furniture item remains completely stationary. This variant is mandatory for workbenches or machine stands.

Treads: Hard Floor vs. Soft Floor Castors

The choice of wheel material must match the flooring precisely. The technical rule of thumb is: a hard floor requires a soft castor, whilst a soft floor requires a hard castor. Just like vehicle tyres, the tread must suit the surface, otherwise you risk scratches, extremely high rolling resistance, or jammed wheels.

• Soft treads (polyurethane, TPR): Usually consist of a hard core with a tyre made of polyurethane (PU) or thermoplastic rubber (TPR). They have a lower Shore hardness and absorb impacts. These castors are mandatory for hard floors such as laminate, parquet, tiles, or polished concrete. They leave no marks and reduce rolling noise.
• Hard treads (polyamide, hard plastic): Made of solid plastic. They are suitable for soft surfaces such as carpets or rugs. A soft castor would create too much frictional resistance on a carpet, whereas a hard polyamide castor pushes through carpet fibres and rolls smoothly.

To make the right choice for your project, carefully match your flooring requirements against our range of furniture castors.

Calculating the Correct Load Capacity

One of the most common errors when building mobile furniture is incorrectly calculating the required load capacity. The load capacity is stated in kilograms (kg) and always refers to an individual castor.

The "n-1" Rule

When a piece of furniture stands on four castors, the total weight must never simply be divided by four. On uneven floors, thresholds, or joints, one castor temporarily loses contact with the ground. At that moment, the entire weight rests on only three castors.

The calculation formula is therefore: `(furniture self-weight + maximum payload) / 3 = required load capacity per castor`

Calculation example: An MDF workshop cabinet weighs 45 kg empty. It will hold tools weighing up to 75 kg. The total weight is therefore 120 kg. 120 kg / 3 = 40 kg. In this case, each individual castor must have a load capacity of at least 40 kg.

Dynamic vs. Static Load Capacity

Manufacturers generally specify the dynamic load capacity. This defines the maximum permissible weight during movement at normal walking pace (approx. 4 km/h) over an even floor. If the furniture is moved rarely and primarily remains in one spot, the static load capacity applies, which is usually significantly higher. For safe dimensioning, however, the dynamic value must always be used.

Criteria for Selecting the Right Furniture Castor

In addition to load capacity and tread material, other physical and geometric parameters determine which castors are suitable for a specific project. You can find the right combination of these features in our furniture castors section.

Wheel Diameter and Overall Height

The wheel diameter influences rolling resistance and starting resistance. The larger the wheel, the easier it is to set the furniture in motion and the more effortlessly it overcomes obstacles like carpet edges, door sills, or joints.

• Small castors (e.g. `30 mm` to `40 mm`) are suitable for under-bed drawers or small pedestals moved only short distances on smooth floors.
• Medium castors (`50 mm` to `75 mm`) are the standard for domestic furniture, coffee tables, and lightweight serving trolleys.
• Large castors (`100 mm`, `125 mm` or larger) are used for heavy workshop trolleys, pallet furniture, or outdoor applications.

The overall height specifies the distance from the bottom edge of the wheel to the top edge of the mounting. This dimension must be deducted from the desired total furniture height during design.

Mounting Types

The load transfer from the furniture to the castor takes place via the mounting fitting. This must be chosen according to the furniture material.

1. Top plate: The most robust mounting type. The castor features a rectangular or square plate made of galvanised steel sheet, usually with four screw holes (e.g. `60 x 60 mm`). It distributes forces over a larger surface area and is traditionally fixed beneath chipboard or solid wood using wood screws.
2. Threaded pin: The castor has a vertical threaded bolt, typically with an M8 or M10 metric thread. This variant requires a matching female thread in the furniture item. A threaded insert or tee nut is commonly set into the timber for this purpose.
3. Push-in stem: Standard for office chairs and lightweight pedestals. The stem (frequently `11 mm` or `10 mm` in diameter) is simply pushed into a matching socket in the furniture and held in place by a circlip. This connection is not designed for heavy lateral shear loads.

Typical Application Areas in Practice

Castor specifications vary widely depending on the application. An overview of common fitting scenarios helps you navigate our furniture castors range.

Workshop and Industrial Use

Workshop trolleys require castors with high load capacities (often exceeding `100 kg` per castor). Large wheel diameters (from `100 mm`) are used here to roll over workshop floors littered with cables or debris. The housings are made of heavy sheet steel, and the wheels often feature roller bearings or ball bearings to minimise rolling friction under extreme loads. A total brake is indispensable in these settings.

Pallet Furniture and Outdoor Units

Furniture made from wooden pallets has a high self-weight. Because it is often moved over uneven decking or paving stones, resilient treads made of thick polyurethane and wheel diameters of at least `75 mm` should be selected. Fitting is almost always done using top plates, as pallet corner blocks provide sufficient surface area for four screws.

Living Areas: Coffee Tables and Sideboards

In living spaces, aesthetics are often just as important as function. Concealed castors (often designed as roller castors) or decorative design castors are popular here. Load capacity is usually a secondary factor (often `30 kg` to `50 kg` per castor is sufficient); what matters most is an entirely non-marking soft tread to protect parquet floors.

Under-Bed Storage and Pull-Out Units

For drawers or storage boxes pulled out from under a bed, small, rigid fixed castors with diameters from `25 mm` to `35 mm` are typically used. They do not need to swivel because the box is guided linearly by the bed frame. An extremely low overall height is the primary requirement here.

Fitting and Technical Installation

Proper installation ensures the longevity of the fixing. A castor that pulls out under load will inevitably cause severe damage to the furniture.

Tools Required

• Cordless screwdriver
• Wood drill bit (matched to the screw or insert size)
• Wood screws / chipboard screws (e.g. `4 x 16 mm` or `4.5 x 20 mm` with PZ or TX drive)
• Spanner (for threaded pins, typically size 13 or 14 mm)
• Tape measure and pencil

Fitting a Top Plate Castor

1. Positioning: The plates should not be mounted flush with the outer edge of the furniture. A setback of `10 mm` to `20 mm` prevents the swivel radius of the castor from protruding beyond the edge of the furniture (a trip hazard).
2. Pilot drilling: To prevent splitting MDF or solid timber, you must drill pilot holes. For a `4 mm` screw, a drill bit with a `2.5 mm` or `3 mm` diameter is recommended. The drilling depth should be around `2 mm` less than the screw length.
3. Screwing into place: Use pan-head screws. Countersunk screws are not suitable for the flat holes of a castor top plate, as their conical head does not sit flat and can damage the mounting hole over time. Tighten the screws in a crosswise pattern.

Fitting a Threaded Pin Using a Threaded Insert

1. Drilling the hole: For an M8 thread, a matching threaded insert is required. The outer diameter of the insert dictates the drill bit size (often `10 mm` or `12 mm` for M8). Drill perpendicular to the end grain or underside of the wood.
2. Driving in the insert: Screw the insert flush into the timber using a hex key. The coarse external thread cuts into the wood fibres, providing exceptional holding strength.
3. Fitting the castor: Screw the threaded pin of the castor into the metric internal thread of the insert and tighten it at the castor hexagon using a spanner.

For specific fixing solutions and suitable hardware, check the detailed product specifications across our furniture castors range.

Care and Maintenance of Furniture Castors

Although furniture castors are generally low-maintenance, occasional care ensures smooth running and protects flooring. The most common daily issue is hair, threads, or dust bunnies winding around the wheel axle. This increases rolling resistance drastically and can cause soft wheels to drag across the floor, leaving scuff marks.

• Cleaning: Regularly remove trapped threads from the axle using tweezers or a craft knife.
• Lubrication: If the swivel bearing of the castor features an open ball race, lubricate it every few years with a drop of machine oil or bearing grease.
• Visual inspection: Check hard treads for embedded grit or stones. These act like sandpaper on hard floors and must be prised out immediately with a small screwdriver.

Frequently Asked Questions (FAQ)

Which furniture castors are suitable for parquet and laminate? For sensitive hard floors, you must choose castors with a soft tread (usually made of polyurethane or TPR). These absorb shocks, leave no marks, and prevent scratching.

How do I calculate the required load capacity correctly? Add the self-weight of the furniture to the maximum payload. Divide this total by 3 (not by 4). The result is the minimum required load capacity that each individual castor must support.

What is the difference between a swivel castor and a fixed castor? A swivel castor features a swivel bearing and rotates 360°, allowing the furniture to be steered in all directions. A fixed castor is rigid and moves only in a straight line, forwards and backwards.

What is a total brake? A total brake is a locking mechanism on a swivel castor that stops the wheel from rolling and simultaneously locks the swivel race when the lever is depressed. The furniture unit is kept completely stationary.

What thread size do threaded stem castors typically have? Most standard castors with threaded stems for furniture construction feature an M8 or M10 metric thread.

Why do my office chair castors drag on carpet? Office chairs are often supplied as standard with soft castors meant for hard floors. On soft carpets, these create too much friction. For carpets, you require castors with a hard tread (usually made of polyamide).

How do I fit castors beneath thin chipboard? The base panel should be at least `18 mm` thick. If the panel is thinner, screws must not be too long to avoid piercing the upper surface. In this case, it is advisable to glue and screw additional timber blocks in the corners to provide enough depth for the top plate and longer wood screws.

Related Categories & Guides

Building mobile furniture often requires complementary hardware to complete the project. For instance, if you are building a mobile workshop cabinet, you will need suitable drawer runners alongside correctly rated furniture castors.

• Drawer runners: Discover how to properly fit full extension runners for heavy tools.
• Screws & fixings: Find the right wood screws with TX drive for securely fastening castor plates.
• Furniture handles: Choose robust bar handles to serve as push handles on your transport trolleys.