NB: This article is archive content first published on towsure.com c.2004

About the National Trailer & Towing Association

The NTTA was founded in 1975 as the Association of Trailer Manufacturers and has since evolved into a wider, modern and dynamic body. The NTTA sets the standards for the towing industry today.

• Giving small, medium and large businesses the added strength of a national organisation.
• Promoting the responsible use of light trailers.
• Improving the skills and expertise of drivers
• Providing Trailer Technician & Towbar Fitter accreditation schemes
• Increasing use of trailers by promoting their benefits.
• Representing industry at Government and EC levels. 

Towing safely and legally:

NTTA & Towsure Disclaimer

The information in this guide is intended as a guide. It is as accurate at the time of publication as the editor is able to make it. Neither the Editor, the NTTA, Towsure nor any other person or company associated with the production of this guide accepts any responsibility for any inaccuracies which may be in the text. 

It is the responsibility of any person wishing to depend on the facts contained in the NTTA's or Towsure's website to check for themselves with original documentation or any updating regulations, instruments or changes in the law.

Matching the Trailer with the Towing Vehicle

It is important that the vehicle you use to pull your trailer is adequate for the job.

• Check that the engine is large enough to tow the trailer and load.
• Check that the brakes are powerful enough to stop the vehicle and trailer safely.
• Check that the Trailer Gross Weight does not exceed the Towing Capacity of the Towing vehicle.

The addition of a loaded trailer to a vehicle will inevitably have a very serious effect on the vehicle's performance. Starting, particularly on hills, can be much more laboured; stopping can take longer distances; cornering and negotiating sharp bends requires extra care. Consider all these things very carefully when choosing and loading (and towing) your trailer.

The paragraphs which follow, refer to the data that is relevant to your choice.  See "The Law"

The most important check is the vehicle manufacturer's recommended towing limit, which should be in the vehicle manufacturer's handbook and on the VIN plate on the chassis.

A good rule of thumb, for safety and stability, when towing a caravan, is the 85% figure recommended for caravans by the Caravan Club. This suggests that you should not tow a caravan that weighs more than 85% of the towing vehicle's kerb weight. (as long as 85% does not exceed the vehicle manufacturer's recommended towing limit). The kerb weight is defined as the weight of the vehicle plus a full tank of petrol and 75kg (for the driver and luggage).

Police Forces  use the manufacturer's recommended towing limit as their guide. Under no circumstances should the vehicle's Gross Train Weight be exceeded. You should also refer to limitations on overall length, details can be found in this guide that deal with trailer dimensions.

Weight Distribution

Loads must be securely tied down or restrained.
 

There must be no load projections outside the trailer that might cause danger to other road users.

Wherever possible, loads should be evenly distributed across the trailer and positioned in such a way as to keep the nose weight within the recommended limits.

Refer to the manufacturer's recommendation and/or the nose weight limit of your vehicle. See also "Attaching the Trailer".

If uneven loads have to be carried, ensure that individual wheels/axles are not overloaded.

It may be necessary to reduce the overall load to achieve this.
 

NOTE: Good Towing practice should always take into account the inevitable effects on vehicle handling, braking and general stability of towing a trailer behind the vehicle.
 

• Dangerous loss of stability when loads are loose and move around. Danger of loads parting from the trailer.
• Load shooting forward when the outfit brakes. This is particularly acute if the load consists of planks, bars, etc, laid in line front to back.
• There is a very significant danger of light items being lifted out of a trailer by the slipstream. All items should be secure.

Loading practice should, therefore, take into account:

• Secure restraint
• Recommended nose weight.
• Balance
• Weight Distribution

Horseboxes and Livestock Trailers

When horses are being towed, they have a tendency to rest most of their weight on their hind legs. Because of this, horseboxes usually have their twin axles set behind centre.
 

(There are strict guidelines for the carriage of livestock, conditions of floors, partitions, tethering points, etc.)

Trailer Checks Before Each Journey

The trailer operator or the driver of the towing vehicle, if different, has the responsibility for the safe operation of the trailer and needs to carry out the following checks:
 

• If the trailer is laden is the load correctly distributed i.e. Not too much or too little nose weight?
• Is the load within the trailer's official payload? - i.e. Not overloaded.
• Is the actual gross weight being towed within the towing vehicle manufacturer's recommended maximum towing limit (whether braked or unbraked.)?
• Is the load correctly secured?
• Are all the lights undamaged and working correctly?
• Are the 7 core cable and plug undamaged?
• Is the correct number plate fitted? (both registration number and style)
• Is the breakaway cable or secondary coupling undamaged and correctly connected, to a suitable point on the tow bar or towing vehicle?
• Are the tyre pressures correct and all tyres free from cuts, bulges and with adequate tread, (including the spare)?
  Tyres must have a continuous tread depth of at least 1.60 mm on cars, light vans and trailers, across the centre three-quarters of the width (1mm for other vehicles)
• Are you satisfied that the wheel nuts/bolts are tightened to the correct torque?
• If required are the mudguards in satisfactory condition and secure?
• Is the trailer correctly coupled to the towball or pin?
• Is the coupling height correct? I.e. Not excessively nose down or nose up.
   

Follow the golden rules of towing:
 

• Make sure the trailer is level when coupled to the towing vehicle
• Make sure the nose weight is between 50 and 100kg (unless trailer is very light.)
• Make sure the tyre pressures are correct.
• Are the jockey wheel and any corner steadies or prop stands fully wound up and secure?

NB. Check the correct operation of damper and brakes as soon as possible after commencement of journey.

Attaching the Trailer to the Vehicle

Become methodical about hitching up and unhitching so that you do not forget anything.
 

If your towcar's mirrors do not give a good view past the trailer you should fit towing mirrors.
 

• Apply the trailer handbrake, remove any towball and electrical socket dust covers and security devices then wind the jockey wheel to the required height. Check the towball is lightly oiled. (Not greased) (If not being used with a head stabiliser.)
   
• Get a helper to stand with their hands showing you where the hitch is (place a broom against it if you are alone) and reverse slowly back. Your helper indicates if you are off line.
   
• Raise the front of the trailer by means of the jockey wheel assembly to the required height, roll trailer up to the rear of the towing vehicle.
   
• If the trailer has tandem axles, raise sufficiently to raise the front wheels clear of the ground to aid maneuverability.
   
• Do not attempt to lift the front of the trailer. Lower the trailer by means of the jockey wheel assembly onto the towball of the vehicle.
   
• Over the last foot or so, your helper should use their hands to show you the actual distance between towball and coupling head.
   
• If you have to stop a few inches short, judge how far back you are going by comparing the front wheels' movement to something on the ground.
   
• Wind the jockey wheel down to lower the coupling head onto the towball.
  - Some coupling heads have a locking handle which stays up then automatically locks onto the ball, others have to be held up and may have an indicator to show when the ball is in place.
   
• Once the coupling head appears locked on, lower the jockey wheel a few turns to lift the back of the vehicle to prove the coupling head is on properly, then fully raise the wheel before unclamping it and, finally, securely locking it fully raised. Check that the wheel in the position you have locked it is not interfering with the operation of the coupling overrun mechanism.
   
• Attach safety breakaway cable(s) to the rear of vehicle. This cable will apply the hand brake if for any reason the trailer becomes detached whilst towing. (Clip the breakaway cable onto the special rings some towbars have or loop it around the bar, making sure it cannot foul the coupling head. Do not loop it round the towball neck unless you can find no alternative.) Check that the breakaway and lighting cables have enough slack for cornering but will not touch the ground.
   
• Plug in the lighting plug, and check all lights and indicators. The electrical plug only fits one way, so line up its cut-out with the lug on the bottom edge of the socket. Some cars have two sockets ñ use the one with the black cover flap because the one with the white flap is for caravan supplementary electrical systems.
   
• It is your responsibility as the driver to ensure all lights work. Turn on the car lights and check the trailer's lights. With the ignition on, make sure the correct indicators are working - car and trailer indicators not matching is a common fault - then get someone to see if the trailer brake lights work. (If you are alone, use a short stick between the pedal and the seat to hold down the brake pedal.)
   
• Adjust both external mirrors so that a view down both sides of the trailer can be obtained. (If this cannot be achieved extension mirrors should be fitted).
   
• When loading a trailer ensure the weight is distributed appropriately. Nose weight is a very important factor in making your vehicle and trailer combination stale during towing. Inadequate nose weight can cause snaking problems. Too much nose weight causes other problems
   
• Noseweight should be at least 50kg when the outfit is stationary. Refer to the recommendations of you vehicle and trailer manufacturers.
   
• It is your responsibility, as the driver, to ensure that your vehicle or trailer is not overloaded.
   
• If the trailer has an eye coupling, after attaching the trailer, make sure that the safety locking catch on the towing pin is properly applied and that the safety pin or clip is fitted.
  (If this is not fitted, the trailer could become unhitched).
   
• Lift up and lock the jockey wheel assembly. (If this is not done, the jockey wheel will become damaged).
   

Driving With a Trailer

Speed limits:
 

Always keep to the legal speed limit for the road you are using.

Speed limits for cars towing caravans or trailers.
 

• 30mph limit applies on all roads with street lighting unless signs show otherwise.
• 50mph applies on single carriageways unless signs show otherwise.
• 60mph applies on dual carriageways and motorways
   

It should be remembered that you must not travel in the right-hand lane of a motorway, with three lanes or more, if you are driving a vehicle drawing a trailer.
 

Drive within your outfit's capabilities:
 

• Always drive at a speed that is well within your capabilities, and to the road and weather conditions that prevail at the time.
• If your trailer begins to snake or swerve, ease off the accelerator and reduce speed gently.
  (This can happen if you are driving too fast or the load in the trailer is wrongly positioned).
• Do not brake sharply on a bend, (this could cause a possible jack-knife situation).
  Reduce speed before the bend and take the appropriate gear for the speed you are doing.
  Then gently accelerate out of the bend.
   

Reversing with a Trailer:
 

• Before reversing, get out of the vehicle and check that all is clear to the rear before making the maneuver.
• Be on the look out for children and pedestrians. If possible, get someone to watch while the manoeuvre is made.
   

See full details on: "Step-by-step Reversing"

WARNING!! Never reverse a trailer without checking behind because of the huge blind spot.
Ideally, have someone see you back, especially in crowded places.
 

Reversing a trailer is a skill that can be mastered with a little perseverance by anyone who has learned the basic theory. Find somewhere with plenty of space and keep trying until you get it right. It helps to have someone who knows how to do it to tell you where you are going wrong.

Step-by-Step Reversing Guide

This example describes how to reverse to the right because that is easier than reversing to the left.
 

If you are not sure which way your wheels are pointing at any time lean out and look at them.
 

Many pre-1989 trailers have a lever that prevents the brakes from operating during reversing.
All braked trailers built after March 31st 1989 have auto-reverse brakes.

1 )  Start with the outfit as straight as possible and about a trailer's length from the place into which you are reversing. You need plenty of room to swing the towcar round.
 

2 )  Watching the trailer out of the driver's window, reverse slowly and start turning the steering to the left. It is easier to add more steering than to correct too much.
 

3 ) As soon as the trailer starts to turn, you begin straightening up whilst still reversing. If you leave it too late, the trailer will 'jack-knife'. (This means that it gets to such an acute angle to the towcar that it can no longer be manoeuvred in reverse. This condition can damage towcars with long rear overhangs.).
 

4 ) Eventually you start steering the other way, while still reversing, to bring the towcar's nose round so that the car "follows" the trailer, but keep an eye on where the trailer is going in case it needs correction
 

5 ) Reverse in a straight line using the door mirrors. Reverse slowly and carefully. When more of the trailer starts to appear in one mirror, steer towards that mirror to start the trailer going the other way. Such corrections only require small steering movements.
 

6 ) Do not get your mind stuck in reverse! If the trailer goes out of line, it may be easier to pull forward to correct it. On tight turns or if it jack-knifes, to pull forward is your only option.
 

The Use of Stabilisers

Stabilisers are not intended to be a substitute for sound practice in loading and towing.
They are valuable, particularly with caravans and horse trailers, and other high-sided trailers.
They will not, however, overcome problems created by poor loading or poor driving.
 

Follow the golden rules of towing:
 

• Set up the trailer so that is level when coupled to the towing vehicle.
   
• Make sure the nose weight is between 50 and 100kg (unless trailer is very light.)
   
• Make sure the tyre pressures are correct.
   

It should be remembered that you must not travel in the right-hand lane of a motorway, with three lanes or more, if you are driving a vehicle drawing a trailer.
 

The main purpose of a stabiliser is to stop a trailer or caravan from becoming unstable and '"snaking" from side to side. They come in various forms and designs. The most popular types are the trailing arm leaf spring and the coupling head stabiliser.

"Snaking" is when the axles of the caravan/trailer move out of line from the towing vehicle.
When this happens, the trailer/caravan tries to move back into line and it goes too far.
This action starts the cycle of "snaking" from side to side. Unless the snaking is stopped, it will increase and will cause the driver to lose control.
 

Snaking can be caused by a number of factors such as:

• Incorrectly placed loads (excessive loading to the rear of the axle(s)
   
• Very light or negative nose weight
   
• Side winds (when a large commercial vehicle or coach overtakes and causes the air to buffet the caravan/trailer, moving the axles out of alignment)
   
• Special purpose built trailers having awkward internal fixtures that may be not balanced, causing instability.
   

To stop snaking there are a few simple rules:

• Keep the vehicle steering in a straight line
   
• Change down a gear and take both feet off the pedals
   
• If the snaking starts whilst going down hill, change down a gear and very gently apply the brakes
   
• Do not try to accelerate out - this could INSERT INTO tmp_cms_page (`title`, `page_layout`, `meta_keywords`, `meta_description`,`identifier`,`content_heading`,`content`,`is_active`,`sort_order`) VALUES ( in disaster unless the vehicle is exceptionally powerful.
   
• Do not brake hard - this may cause the trailer to jack knife.
   
• Do not try to steer out - it is very difficult to read the snaking action and it can make it worse.
   

Stabiliser Checks:
(Each manufacturer will have their own servicing and checks guide, which should be contained within the handbook or fitting instructions.)
 

Stabilisers must be checked at the start of each journey
 

• Check that the friction is apparent (if possible)
   
• Check that the stabiliser fits into its locating place properly
   

Stabiliser Servicing:
 

Stabilisers must be overhauled thoroughly at least once a year or after 20K miles towing. (whichever is sooner). The stabiliser must be dismantled and any pads or friction disks must be inspected for cracking or excessive wear. NB: Beware of servicing older stabilisers because the friction pads or disks may contain asbestos. These should be handled and disposed of carefully

Trailer Lighting Requirements

Trailers must have on the back two red sidelights, two red stop lamps, an illuminated number plate and two triangular red reflectors plus amber indicators designed to flash between 60 and 120 times per minute. If they are more than 1.3m wide, they must also have at least one red fog lamp. All trailers built after Sept 30th 1990 require front reflectors. They must have front reflectors and, if they are more than 1.6 metres wide, front position lights.
 

Requirements:
 

• If, in the case of direction indicators, it is not possible to meet the maximum height requirements, this dimension can be increased to 2300mm.
   
• If, in the case of the rear position (tail) lamps and stop lamps, it is not possible to meet the maximum height requirements, this dimension can be increased to 2100mm.
   
• On trailers manufactured after 1 October 1985, the maximum height of the red triangular reflectors can be increased to 1200mm if necessary.
   
• Trailers manufactured after 1 October 1985 require numberplates, illuminated by an 'E' or 'e' marked lamp. If a clear window in the rear position lamp is approved, this can be used instead of a separate numberplate lamp but must be fitted to the manufacturer's instructions with regard to distance from the numberplate.
   
• At least one rear fog light is mandatory on trailers over 1.3 m wide. Two lamps are preferred but, if only one is fitted, it must be to the offside or on the centre line of the trailer.
   
• No maximum distance from the outer edge of the trailer is stated for a fog lamp(s) but there must be a minimum distance of 100mm from the stop lamp.
   
• The distance of the direction indicator from the side of the trailer may not exceed the actual distance of the rear lamp by more than 50mm.
   
• Trailers manufactured after 1 October 1985 which are more than 1600mm wide, (except boat trailers) require front position lamps (clear lens).
   

Certain trailers must have side position lights which show white to the front and red to the back. In addition, trailers over certain lengths must have amber side reflectors.

Trailer Number Plates

The ability for a numberplate to be read is covered by Statutory. Instrument 1971 No 450 - The Road Vehicles (Registration & Licensing) Regulations 1971. Part Ill - Exhibition of Licences and Registration Marks states the following:
 

1. The provisions of this regulation shall apply to vehicles, other than works trucks and agricultural machines, first registered on or after 1 October 1938.
    
2. The registration mark of the vehicle shall be fixed and displayed on both the front and the back of the vehicle, so that in normal daylight the letters and figures are easily legible from every part of the 'relevant area', the diagonal of the square governing the 'relevant area' being 75 feet.
    
3. For the purposes of this regulation, the expression 'relevant area' in relation to a registration mark on a vehicle means the area contained in a square described on the ground, either in front of or behind the vehicle, where one corner of the square is below the middle of the registration mark and the diagonal of the square from that corner is parallel to the longitudinal axis of the vehicle, but excluding any part of the square within 10 feet of the vehicle - see diagram.
    

It is an offence to allow the numberplate to be obscured. This is now a fixed penalty offence, and therefore more likely to be policed. Obviously, this is of some concern to towbar fitters and to drivers of vehicles with towbar attachments.

Trailer Brake Requirements

• Braked trailers manufactured pre Oct. 1982 may be fitted with a spring damped coupling as a replacement item.
   
• Braked trailers manufactured after Oct. 1982 must be fitted with a coupling that incorporates a hydraulic damper.
   
• Braked trailers manufactured after Oct. 1982 require brakes that comply with EC Directives. If brakes are required, all wheels must be braked. (if manufactured in or after 1968)
   
• Any braked trailers manufactured after April 1989 must be fitted with a hydraulically damped coupling and auto reverse brakes to give braking efficiencies required by EEC Directive 71/320 (ECE13).
   
• The size of the ball coupling on braked and unbraked trailers must be 50mm to ISO and BSI Standards. The use of old 2-inch unit is not recommended.
   
• Unbraked trailers manufactured after 1 Jan 1997 must be fitted with a secondary coupling that will provide some residual steering in the event of an unplanned uncoupling. This device should also prevent the ball coupling hitting the ground in similar circumstances. It must be connected to the towing vehicle when the trailer is being towed.
   
• Braked trailers must be fitted with a parking brake that operates on at least two road wheels on the same axle. At all times it must be capable of being maintained in operation by direct mechanical action without the use of hydraulic, electric or pneumatic systems - i.e. Operated by rod or cable action. The efficiency of the handbrake must also comply with EEC Directive 71/320/EEC; i.e. It must be capable of holding a stationary trailer on a gradient of at least 16% (1 in 6.25)
   
• An emergency breakaway cable must be fitted to the parking brake linkage and the other INSERT INTO tmp_cms_page (`title`, `page_layout`, `meta_keywords`, `meta_description`,`identifier`,`content_heading`,`content`,`is_active`,`sort_order`) VALUES ( clipped or fixed round some fixture on the towing vehicle so that, in the event of the trailer becoming detached from the towing vehicle, the cable will apply the parking brake automatically, before snapping itself. It is not recommended to loop the cable round the towball. (But do so if there is no alternative attachment point.) It is a separate offence not to use the breakaway cable provided.
   
• A secondary coupling as per ( F ) must be fitted to a braked trailer manufactured before 1982 that has a manual handbrake arrangement . (A secondary coupling can also be fitted to a braked trailer with hydraulic damping, manufactured after 1982. In such cases, great care should be taken to ensure that the secondary coupling is appropriate in terms of the weight of the trailer (esp. If it is over 1000kg.). Also the operation of the breakaway cable is likely to be prejudiced.)

Trailer Eyeshafts

No specific legislation applies but the use of products complying with BS A.U. 24a 1989, which specifies the pin/hook and eye dimensions, together with throat clearances of the jaw to ensure adequate articulation, is strongly recommended.

The eyes normally used in the U.K. have an internal diameter of 30, 40, or 50mm and are used with either a towing jaw, a combination jaw/towball or occasionally a hook. There is also the 76mm Nato eye used by the Armed Forces, usually with a military style pintle hook.

The British eyeshafts have a round or toroidal section eye and are used with a parallel type pin with sufficient clearance in the eye to permit the correct sequence of towing on the pin and braking on the jaw. If the pin is too large or the clearance between the jaw and pin too great, then both towing and braking loads will be put onto the pin.

A 40mm DIN eye, commonly used in Europe, has a hardened steel bush fitted to the internal bore and is designed to be used with a special pin that has a bulbous or reinforced section, around which the eye can pivot. Because of this it is ESSENTIAL that a 40mm DIN eye is NOT used with a British style parallel pin, as the sharp edges of the bush will cause accelerated wear of the pin, with possible serious results. The incorrect combination can also often prevent full articulation of the eye within the jaw, leading to rapid coupling wear and possible chassis damage.

If a trailer of less than 3500kg gross weight is to be towed by an H.G.V. it is recommended that an eye is used in preference to a 50mm ball coupling. In this way the overrun coupling is better able to withstand the additional forces imposed on it by the harder suspension and possible extra overhang behind the rear wheels on the towing vehicle.

Towing Jaws & Hooks

British standards require that there should be sufficient room behind the pin of any towing jaw to allow a bar of 31.75mm (1.1/4") to be passed through. This ensures adequate articulation of the eyeshaft in both vertical and horizontal planes. It is also important that this gap is not too great, thus allowing the back of the eye to hit the front of the pin before the front of the eye contacts the throat of the jaw.

A jaw opening that does not comply with the standards and therefore restricts articulation upwards and downwards, is likely to bring about stress fractures on either the coupling or the trailer chassis drawbar. This may be particularly pronounced if the towing vehicle has a long overhang behind the rear wheels and, in such cases, the fitting of more robust, higher capacity equipment than the gross trailer weight might suggest, is often recommended.

The above standards also apply to the jaw on a combination jaw and towball unit. This type of product provides the flexibility of being able to tow trailers fitted with either an eye or 50mm coupling head, without having to change the fittings on the tow vehicle. Where the ballpin is separate, it is also preferable to use a unit that is fitted with a primary locking device to stop the pin/ballpin working loose or rattling unduly. A secondary device such as an "R" clip is also often used, but if this is the only means of securing the ballpin it is insufficient, due to the stresses imposed by the alternating lifting/dropping forces brought about by road conditions and/or poor load distribution.

A hook has no separate pin, but a safety catch should be fitted to prevent inadvertent detachment of the eye. Where a hook has no "chin" or limiting pins on its outer face the towing eye may swing round and underneath the hook if the trailer has been reversed into a jack-knife position. In such a situation, as the towing vehicle moves forward, the eyeshaft and/or drawtube can be severely bent.

Trailer Wheels

There are many different types of wheels fitted to trailers, many of them specifically for trailer use. The practice of using car wheels, rather like that of using car brakes, has largely died out.

Wheels, like tyres, have a maximum weight capacity determined by the manufacturer.

Where a wheel/tyre unit maximum weight capacity is declared, if either of the two parts has a different loading capacity, the declared figure will be the lower of the two. Reference should always be made to the supplier if there is any doubt.

The technical terms around a wheel are frequently misused and "rim" and "wheel" are often misused. The main factors to bear in mind, particularly when ordering replacements are as follows:

1. Rim: The rim serves as the seat for the tyre
    
2. Wheel Disc: The wheel disc connects the rim with the hub.
    
3. Wheel: The wheel is the entire assembly, consisting of the rim and disc
    
4. Rim width: The width inside the wheel flanges and is normally expressed in inches e.g. 4.50.
    
5. Rim diameter: The diameter of the wheel just inside the rim, where the inner edge of the tyre bead sits and normally expressed in inches e.g. 13"
    
6. Offset: The distance between the seating surface of the wheel/hub and the vertical centre line of the wheel/tyre unit. This can be positive offset, as shown above, where the vertical centre line is behind the seating point, when the wheel is fitted to the hub. Negative offset is the opposite and is sometimes known as inset.
    
7. Centre disc: There are also centre disc wheels that have neither positive nor negative offset; i.e. The vertical centre line is in exactly the same plane as the seating point.
    
8. Centre bore: The hole in the centre of the wheel disc, designed to accommodate the bearing boss and grease or dust cap. Size expressed in millimetres.
    
9. Stud or bolt holes: The holes by which either the studs or bolts fasten the wheel to the hub. Normally 4 or 5 in number, the size is determined by the size of the stud or bolt, either metric or imperial. The usual way of expressing the configuration incorporates both these factors, e.g.
   
   4 x M12 = 4 off 12mm studs or bolts.
   5 x M14 = 5 off 14mm studs or bolts.
   4 x 12 = 4 off 12 studs.
   
   The seating of the stud hole is also important and must correspond with the seating on the stud or wheel bolt. These are either conical (Straight side walls inside the seating) or spherical (curved side walls inside the seating) but there are some continental wheels with flat cylindrical holes.
    
10. Pitch circle diameter (P.C.D.): The diameter of the circle around which the studs are arranged. Measurement given in metric or imperial e.g. 100mm, 112mm, 5.5", 4". The measurement of a 4 stud fixing is simply the distance between the centres of two opposite stud holes.
    
    A five stud fixing is calculated by taking the measurement from the centre of a stud hole to the edge of the centre bore x 2 + the diameter of the centre bore.
     
11. Studding patterns: The correct way to express a studding pattern, either of a wheel or of a hub is an amalgam of 9) and 10),
    
    E.g. 4 x M12 on 100mm
    4 x 1/2" on 5.5" (or 139.7mm)
    5 x M12 on 112mm
     
12. Two piece wheels: Although rarely used as original equipment in today's light trailer market, a number of older trailers may be fitted with two piece wheels, particularly those using 600 x 9 tyres. It is vitally important that the nuts holding the two sections together are NOT loosened whilst the tyre is still inflated.

Essential information when refitting trailer road wheels: "Wheel Bolt Tightening"

Trailer Tyres

Tyre condition:
Car and trailer tyres must have at least 1.6mm of tread over the central 75% of their width for their entire circumference, although a tyre with under 3mm offers little grip in the wet. Tyres must be free from deep cuts and bulges (which indicate they are breaking up) and it is illegal to use cross-ply and radial tyres on the same axle. (Make sure that the tyres you fit to your trailer are of the correct rating.)

Additional Tyre information:
See links below for detailed tables on Tyre Load Index, Speed Symbols and Pressure Ratings.

• Tyre Load Index
• Speed Symbols
• Load and Pressure Ratings:

Tyre sidewall markings :

The illustration below provides an explanation of the markings currently found on a tyre sidewall.
 

* do not apply in the U.K.

Retreads - must also show either 'RETREAD' or 'REMOULD' on the sidewall, together with 'BSAU 144' in place of ECE Type Approval Mark.

Aspect ratio - ratio between the height of the sidewall and the width of the tread, expressed as a percentage. In the example above, the figure is 70%.

Nominal section width - on radial tyres this is expressed in millimetres, on cross ply tyres, inches are used.

Maximum Trailer Dimensions

Towing vehicle under 3500kg GVW

• Length (excluding the coupling and drawbar): 7.0 metres
• Width Maximum: 2.3 metres
  

Towing vehicle over 3500kg GVW

• Length (excluding the coupling and drawbar): 12 metres if at least 4 wheels
• Width Maximum: 2.55 metres
   

• Length of towing vehicle and trailer combined: 18 metres
• Maximum overhang of load from rear of trailer: 3.05 metres
   

Marking of rear overhang

• Between 1m and 2m, ensure the INSERT INTO tmp_cms_page (`title`, `page_layout`, `meta_keywords`, `meta_description`,`identifier`,`content_heading`,`content`,`is_active`,`sort_order`) VALUES ( is clearly visible by attaching a piece of cloth or similar.
• Between 2m and 3.05m, a marker board as defined in the Regulations must be fitted and illuminated at night.

If the overhang is more than 3.05m, an attendant must be carried and the police must be notified 2 days before commencing the journey.
 

"Long Vehicle" Marker Plate: Not required for light trailers.

These are a legal requirement only for trailers over 3500kg or where the towing vehicle is over 7500kg gross weight. When they are required, different plates are required depending on the length of the vehicle. Details can be found in the Road Vehicle Lighting Regulations, Schedule 18.
 

Loads must not project more than 305mm either side of the trailer, up to a maximum width of 2.9m.
 

Loads over 2.9m in width are classed as abnormal loads and the police must be notified two days before a journey commences.
 

Recommended maximum height:
3.0m high or 1.7 times the wheel track. (horizontal distance between centre lines of tyre treads)
There is no legal requirement, but this is an accepted guideline.
If however the height does exceed 3.0m then a notice giving the height details must be displayed in the cab of the towing vehicle. (Only buses are subject to a maximum height regulation).
 

Maximum Trailer Weights

Type 01: Unbraked trailers - max. 750kg gross trailer weight or half the towing vehicle's kerb weight - whichever is less.
 

Type 02: Trailers on overrun brakes - max. 3500kg gross trailer weight

1982 regulations demand that all trailers, including unbraked ones, must be clearly marked with their maximum gross weight in kg. This may be checked at any time by the police at a weighbridge. Since 1st January 1997, all unbraked trailer plates must show the year of manufacture.

To comply with the D.o.T. Code of Practice for the recall of defective trailers less than 3500kg G.V.W. it is desirable that a trailer should carry a manufacturer's plate clearly showing

 

• Manufacturers name and address chassis or serial number and model number
   
• Number of axles
   
• Maximum weight per axle maximum
   
• Nose weight of coupling
   
• Maximum gross weight (G.V.W.)
   
• Date of manufacture

Driving Licence Requirements

Summary:
 

You must hold a full driving licence to tow anything.
 

Most drivers who passed their test before 1 January 1997 have licence categories allowing them to drive vehicle and trailer combinations weighing up to 8.25 tonnes.
 

With effect from 1 January 1997 the second EC Directive on Driving Licences (91/439/EEC) came into effect, affecting new drivers passing their test after that date and HGV drivers who obtained their licence after 31 December 1991.
 

The net result is that new drivers will only be allowed to drive and tow the following combinations:

• Vehicles up to 3.5 tonnes (category B) with a 750kg trailer (4.25 tonnes total MAM).
   
• Category B vehicles with larger trailers i.e. > 750kg, provided that the combined MAM does not exceed 3.5 tonnes and the gross MAM of the trailer does not exceed the unladen weight of the towing vehicle. To be able to tow combinations outside this ruling requires the passing of an additional test.
   
• New HGV drivers and those who have passed their HGV tests since 1 January 1992 will be restricted to towing trailers up to 750kg until they pass an additional test.

Detail of the Regulation
 

The Motor Vehicles (Driving Licences) (Amendment) Regulations 1990 SI 1990 No 842 classifies vehicles according to either:
 

• "Maximum authorised mass" (permitted maximum weight). Vehicles over 3,500kg MAM are classified as LARGE GOODS VEHICLES (LGV's)
   
• Number of seats. Vehicles having more than 8 seats (not including the drivers) are classified as PASSENGER CARRYING VEHICLES (PCV's)

Requires ADDITIONAL qualifications for people to drive LGV's and PCV's

Vehicle Categories

The main non - LGV (unified) licence categories are:
 

Category A:    Motor cycles (with or without a sidecar), including tricycles and mopeds

Category B:    Motor vehicles with:

• A maximum authorised mass (MAM) not over 3,500kg
• A maximum of 8 seats (not including the driver's seat)

Trailers being towed by vehicles in this category must either:
 

• Be not more than 750kg MAM - making a maximum authorised Train Weight of 4,250kg
   
• Have a MAM which does not: - exceed the unladen weight of the towing vehicle
   
• Have a MAM which does not: - Have a train weight exceeding 3,500kg
   

Drivers of vehicles in this category wishing to tow trailers which do not comply with either of the above conditions must have a B + E entitlement.

Categories of LCV Licences

Category C1:

Rigid goods vehicles over 3,500kg but NOT over 7,500kg. Vehicles drawing trailers not over 750kg maximum authorised mass are included in this category
 

Category C1+E:

Combinations of vehicles in Category C1 plus trailers over 750kg maximum authorised mass, but with an overall maximum authorised mass (gross train weight) not over 12,000kg
 

Category C:

Rigid goods vehicles over 3,500kg maximum authorised mass (MAM - this expression has the same meaning as permitted maximum weight - PMW). Entitlement holders may also draw trailers not over 750kg MAM.

Category C+E:
Articulated vehicles and drawbar combinations whose semi - trailers and trailers have a MAM greater than those stipulated in Category C
 

NB: The 'E' relates to trailers and semi-trailers over 750kg maximum authorised mass.
 

These categories are for drivers who previously held old style ("ordinary") licences (in either Group A or Group B) issued before 1 June 1990 allowing them to retain their previous entitlement under the old style ordinary licences.
Drivers in these two categories are also permitted to drive PCV's provided they do not:
 

• Carry more than 8 passengers
   
• Use the vehicle for 'hire and reward' work

Glossary of Terms Used

Unladen Weight (UW):

The weight of the trailer (or towing vehicle) less removable optional equipment and load
 

Gross Weight:

The total weight of the trailer (or towing vehicle) and load
 

Gross Vehicle Weight (GVW) or Gross Weight Mass (GWM):

The total weight of the towing vehicle and its load
 

Maximum Gross Weight (MGW):

The maximum figure set by the manufacturer for the gross weight. This will normally be the technically permissible maximum based on the carrying capacity of the tyres, axles, coupling, suspension and chassis but may have been adjusted downwards for commercial reasons
 

Technically Permissible Maximum Weight:

The technically permissible maximum based on the capacity of the tyres, axles, coupling, suspension and chassis
 

Maximum Authorised Mass (MAM)

As maximum gross weight above. The latest EC term as used in the Driver Licensing Regulations
 

Gross Train Weight (GTW)

The maximum allowable combined weight (combined MAM) of the towing vehicle and trailer as set by the towing vehicle manufacturer
 

Payload:

The difference between the gross weight of the trailer and its unladen weight, i.e. The load carrying capacity
 

Kerb Weight / Kerbside Weight

The weight of the towing vehicle (without payload), including all fluids required for operation (95/48/EEC: Vehicle, 90% full tank, 68kg driver and 7kg luggage.)
 

Vertical Static Load / Nose Load

The weight imposed on the towball or eye by the trailer coupling

Information courtesy of the NTTA (National Trailer and Towing Association)