Castor and wheel selection information

How to choose the right castors and wheels

Make sure the wheel diameter is suitable for the trolley

The most common mistake when fitting castors is to fit wheel diametres too small for the real needs of the trolley and its user. The surveys, both in Australia and overseas, show again and again that small castors which get caught in uneven floors, ridges, gaps and holes, cause many injuries. Large diametre wheels, as against small wheels, will often add much less than 10% to the cost of the trolley and yet make that trolley 500% easier to use.

The guide is for a minimum diametre of:

• 125mm (5") for non-patient trolleys

• 175mm (7") for patient trolleys used indoors

• 200mm (8") for trolleys used out of doors or for loads over 200 kg

• Small castors can still be used in restricted circumstances, for instance around the beds for use on the lightest equipment, in general castors of:

• 100mm (4") size are recommended up to 120 kg trolley loads but only on smooth floors and for short distances, thus they can be used on ward furniture, but not on catering equipment.

• 75mm (3") are even more restricted, being recommended only up to 100 kg trolley loads and again only on smooth floors without obstructions for short distances.

• 50mm (2") are recommended only up to 80 kg trolley loads and for very short distances. If used on carpets a maximum load of 50 kg is appropriate.

• The research is absolutely clear – large diametre wheels reduce forces for all trolley movements.

Larger wheels

• Are easier to roll along the length of corridors or over ridges (eg. at the end of carpets into lifts).

• Reduce vibration to patients and equipment; reduce shock to the users arms from impacts.

• Are more robust/resistant to damage, remain functioning efficiently for longer.

Castor features which effect push and ride comfort

• Tyre material.

• Tyre width and profile.

• Bearing type (in the wheel and the castor head race).

• Use of threadguards.

• Type and number of castor brakes (including direction lock).

Correctly fitted castors for maximum efficiency

To do its job properly, a castor must swivel and roll easily. It can only do this when the trolley and the castor are the right size, and the castor is properly fitted.

When the goods are to be moved in a relatively limited area, either during manufacture, or to and from storage, mobile trolleys are the easiest way. Most industrial codes restrict the direct lift of an adult to 13-18 kg.

Using wheels and castors allows this same person to move 600-1800 kg, but greater loads require mechanical assistance. On average, using modern castors such as ours, a fit adult can push 600 kg continuously, or 1200 kg for 10 metres or 1800 kg for one metre given appropriate tyres and floors.

If greater loads are to be moved there is a clear case for towing the trolley with a tractor of some sort.

Design of trolleys

The responsibility for the design of the trolley must ultimately rest with our customers. Good castors can make a well designed trolley work even better, but they cannot do much to improve a wrongly designed trolley. In general the most comfortable shape for a trolley is one where the sides are about 11/2 to two times the width, and not too high.

A good trolley design should be:

• Not too wide: They have to go through doorways. Hand pushed trolleys have to be at least 80mm narrower than the narrowest doorway and that is across the buffers (corner, leg or strip) which should be fitted). Towed trolleys need to be at least 500mm narrower than the narrowest aisle or doorway, and more if towed in a train.

• Not too long: Otherwise it will not track smoothly around corners. If it must be long you may need to experiment to find the best castor arrangement to suit your particular needs.

• Not too high: Most trolleys are restricted in width to suit the aisles, and will topple over if too high. High trolleys you canNot see over are a safety hazard.

• Not too light: As a rough guide the weight of the trolley is usually 15% to 20% of the load it is to carry. For the castor to function properly the frame of the trolley must be strong enough to hold the castor head truly vertical so it can rotate freely (that is the mounting plate must remain horizontal), and the frame must Not bend under the impacts that invariably occur. The most common cause of castors Not tracking properly is that the mounting has twisted off square.

• Not too heavy: It is often safer, and more efficient, to divide a heavy load over a number of trolleys rather than concentrating it into one. Trolleys which are too heavy to move conveniently remain unused, or people suffer back injuries.

Castor arrangements for hand pushing

Direction of travel	Manoeuverability	Stability	Steering	Comments
	Maximum. Can be moved at right angles.	Good except on narrow trolley.	Erratic if moved quickly over uneven surfaces.	Most popular for confined spaces.
	Good except in confined spaces.	Very stable. Can negotiate ramps easily.	Accurate. Push with rigid castors leading if heavy loads or uneven surfaces.	For more open spaces or long runs some castors have directional lock.
	Very good but cannot negotiate ramps.	Fair except if heavy loads placed on corner.	Accurate	Rigid castors usually next larger size so will rock on two centre wheels.
	High. Can be turned in own length but not moved at right angles.	Most stable.	Best for long wheelbases and straight lines.	Centre castors can be equal or larger in height to end castors.

Castor fitting tips and instructions

• Castors won't roll easily if they're not big enough for the load and floor conditions. The heavier the load, the larger the wheel needed.

• Castor wheels with a 75mm (3") diameter should only be used on lightweight, seldom used equipment.

• Even wheel diameters of 100mm (4") are only useful on smooth floors.

• Any trolley wheeled quickly, or on uneven floors, needs 125mm (5") diameter wheel or larger.

• Hard treads roll most easily on smooth floors, but may cause damage, and are difficult to roll over obstructions. Most people can exert 17 kg of push to get a trolley rolling, and about 12 kg to keep it moving, while reducing to 6 kg over long distances. This is the reason that ball bearings are more popular than plain bearings, as they allow more load for the same push effort.

• Castors will not swivel properly unless they are mounted vertically. Otherwise they will track to one side.

Some recommendations

• Plate mountings: Heavy industrial trolleys need plate mountings, but the base of the trolley must be strong enough to withstand strains. Never mount a plate castor by three bolts only. Never skimp on the mounting base. Remember if the castor does not stay mounted squarely, it will not swivel freely.

• Medium duty castors are often mounted into tubular legs, but again it is important that these legs stay vertical. We recommend that the leg never extend more than 125mm (5") below the nearest support, and (apart from the lightest uses), the tube should be 1.4mm (1.7G) thick or more. Thinner gauges often split. If you wish to use lighter gauge in the rest of the trolley, insert a sleeve for at least 150mm (6") where the castor is mounted.

• Square and round fittings: Never put a round expanding fitting into a square tube. The first time a trolley hits a bump, the tube will elongate, and the castor will fall out. We do have square fittings, and ask that you do use them. If for some reason you need to put round into square, then weld an insert sleeve of round tube (remember – our smallest fitting needs 3/4"ID).

• Directional Lock castors: When using Directional Lock (DL type castors) it is best to use the solid swivel stem (A type) and weld or bolt it in, as screwed types can become misaligned. To achieve the best performance from the larger 175mm and 200mm castors, use solid stems. If rigid and swivel castors are to used together, have the rigid castors at the front, making it easier for it to turn.

Greasing castors

Grease in both the swivel and the wheel serves three purposes:

1. It prevents rusting of the balls and raceways.

2. Prevents galling.

3. It reduces noise.

Not a lot of grease is needed. Too much is unsightly and only attracts dust. A liberal smear is all that is needed. If you only have a few castors to grease, use your finger to apply the grease, then wipe off the excess with a rag.

Tips on greasing multiple castors

• Turn the trolley upside down and remove the wheels.

• Re-grease the head, either through the grease nipple if fitted, or by a chisel nosed fitting on a grease gun. You will need to lift the seals on the heavier range of castors with a sharp pointed screwdriver. Two full squirts are usually adequate, but make sure enough grease gets through to the centre so it can descend to the bottom race.

• Check the wear of the axle bushing. Reuse if not heavily worn, otherwise replace. Smear about a teaspoon of grease along the inside of the wheel bearing with your finger, taking care to force the grease up into the rollers and reassemble. Be careful of the lip seal on the wheel as you reinsert the axle bushing into the roller bearing wheels. Make sure the axle bushing is clean as you reinsert it.

• Reassemble the wheel into the castor. Replace washer where fitted. A drop of Locktite High Assembly Strength solution on the axle is a good precaution.

• Use a no.2 bearing grease (not sodium based).

Castor wear and maintenance

Swivel castors

All but the V series castors have the races staked during assembly so therefore do not require any adjustment throughout their operating life. V series would seldom need adjusting.

Wheel bearings

Any slackness present in plain bearings or roller bearings can often be improved by replacing the axle bushing. If necessary the plain or roller bearings can be replaced as well. Often simply re-greasing B type bearings is enough, though they can also be replaced if necessary. Sealed precision Q type bearings seldom wear sufficiently enough to need attention.

Wheels

Polyurethane wheels usually outlast any trolley to which they are fitted, such is the wear resistance of polyurethane. In general all our wheels are designed with adequate tread thickness for long life and allow for replacement rather than repair.

Tube fittings

It is advisable that any tube fitting on pintle castors be checked after the first 3 months, and then yearly to make sure the tube fitting is fully and firmly into the tube and the tightening nut is firmly but not over tightened.

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Choosing the right wheels for push effort and ride comfort

Major design factors that affect wheel selection

Push effort on smooth floors
The amount of force required to push equipment on smooth floors such as vinyl, commercial carpet and smooth concrete.

Push effort on rough floors
The amount of force required to push equipment on rough floors such as bitumen or over obstacles like elevator door jams and joins between tiles and carpet.

Ride comfort
The user-experience due to the degree of tyre ‘suspension’ and the amount of vibration (and resulting noise) absorbed by the tyres.

Push effort and ride comfort are affected by

Major design factors that affect wheel selection

1. Wheel diameter
   The larger the wheel, the easier to push and the better the ride comfort (ability to pass over bumps and to minimize vibration).
   Why? The larger the wheel, the smaller obstacles are as a proportion of the diameter, resulting in greater momentum.
2. Tyre hardness/resilience
   Hardness: The harder the tyre, the less out-of-round the tyre will be under load, and the smaller the resulting force required to start the wheel from rest on smooth floors.
   Resilience (hi-res): The greater the resilience (bounciness/spring) of the tyre, the lower the sustained push effort required to pass over the multiple obstacles (rough ground).
   Why? High resilience materials return energy after compression just like a running shoe (think super balls vs. squash balls – same hardness, different bounciness).

General factors in wheel selection

In addition to wheel diameter and tyre hardness/resilience the following design factors should be considered:

1. Flat spotting
   The compression set (failure to spring-back to original shape) of tyres after long periods under static loads (permanently distorting to out-of-round)
2. Floor marking
   The damage to floors (cracks, grooves, scratches, marks, streaks or stains) caused by excessively hard tyres or non-colour-stay pigments in tyres.
3. Wear resistance
   How quickly abrasion (due to frequent travel on rough surfaces) will cause the tyre to wear away.
4. Particle embedment
   The degree to which particles such as swarf or pebbles will get stuck in the tyres (which may then cause damage to floors)
5. Tyre profile
   Domed tyres require less force to swivel a wheel (and are generally used in our light to medium duty castor ranges) – Note that most Fallshaw light to medium duty castor ranges brake on the sides of the wheels and rely on our domed profiles. Flat profiles spread load and prevent damage to floors at high load ratings (and are used in our heavy and very heavy industrial duty ranges). 
6. Bearing type
   Some bearings are built to last (hard internal ball tracks or wearing surfaces) with low friction. Others are simpler bearings designed for cost reduction. In general pedestal bearings, precision ball bearings and roller bearings result in lower friction and push effort, with simpler ‘plain bearings’ being good for corrosion protection and low cost.
7. Special conditions of use
   Specialized applications or conditions of use (such as extreme temperatures or corrosive conditions) will also affect
   wheel selection – refer to the ‘specialized castors’ pages and to our website for more information.
8. Castor arrangement (configuration of swivels & fixed)
   Ease of steering is dramatically affected by the castor arrangement (use and positioning of fixed and swivel castors)

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General factors in wheel selection

Tyre material		Flat spotting	Floor marking	Wear resistance	Particle embedment
Energy absorbent elastometers	R	OK	Poor	OK	OK
	S	Good	Excellent	Very Good	Good
	T	Good	Excellent	Very Good	Good
	J	OK	Excellent	Excellent	Good
	A	OK	Very Good	Very Good	Good
	O	Good	Good	Good	Good
Hi-res elastometers	B	Very Good	Excellent	Very Good	Very Good
Urethane & PVC*	U	Excellent	Very Good	Excellent	Excellent
	V	Good	Good	Good	Good
Plastics	N	Excellent	OK	Very Good	Very Good
	H	Excellent	OK	Very Good	Very Good
	P	Excellent	OK	Poor	Poor
	K	Excellent	OK	OK	Excellent
	W	Excellent	OK	OK	Excellent
Sandwich	D	Excellent	OK	Very Good	Very Good
Cast Iron	C	Excellent	Poor	Excellent	Excellent
Foamed	F	OK	Excellent	OK	OK