5. Axles, wheels, tyres and suspension

In this section

5.2.1. Road wheel and hub

Defect	Category
(a) A wheel: (i) with a loose or missing wheel nut, bolt or stud (ii) with more than one loose or missing wheel nut, bolt or stud	Major Dangerous
(b) A spigot mounted wheel hub: (i) excessively worn or damaged (ii) worn or damaged to the extent that wheel security is adversely affected	Major Dangerous

5.2.2. Road wheel condition

You only need to inspect the road wheels fitted to the vehicle at the time of the inspection. If you notice a defect on a spare wheel, you should tell the vehicle presenter about it.

You must not remove wheel hub caps.

You can accept abutting ends on detachable spring retaining rings on wheel rims of semi-drop centre type (identified by the ends of the ring shaped to interlock) as long as the retainer is adequately and safely located in the wheel rim.

Defect	Category
(a) Any fracture or welding defect on a wheel	Dangerous
(b) A tyre retaining ring: (i) not correctly fitted (ii) likely to come off	Major Dangerous
(c) A wheel: (i) badly distorted or wear between wheel and hub at spigot mounting (ii) distorted or worn to the extent the wheel or tyre is likely to become detached	Major Dangerous
(d) A wheel and its fixings not compatible	Major

5.2.3. Tyres

You only need to inspect the tyres fitted to the road wheels at the time of the inspection. If you notice a defect on a spare tyre, you should advise the vehicle presenter.

Size

The aspect ratio of a tyre is included in the size marking. For example, a 215/55R15 has an aspect ratio of 55%.

'Standard' car tyres have a nominal aspect ratio of 82% (unless marked otherwise) and these are almost identical in size to tyres with an aspect ratio of 80%. They can be safely mixed in any configuration on a vehicle.

Some tyres may be marked with two sizes. For example, a 185/75R14 tyre may be dual marked 185R14. In such cases, you can accept either marking.

Load rating - Classes 5 and 7 only

A tyre load rating table is in Appendix B.

Make sure the tyre load rating is suitable for the axle weight.

You can find the permitted maximum laden weight of an axle on the manufacturer's plate.

If axle weights are not displayed on the manufacturer's plate, you must assume that the load capacity of the tyres are suitable, unless there's indisputable evidence to suggest otherwise.

If a goods vehicle has a 'Ministry' plate showing lower axle weights not to be exceeded in Great Britain, you must use those instead of the ones on the manufacturer's plate.

Speed rating - Classes 5 and 7 only

A tyre's speed rating is shown on the sidewall as a letter and usually precedes or follows the load rating. Speed ratings from A to K are unacceptable, with the exception of H.

If no speed rating is shown it must be assumed that the minimum requirements are met.

Load ratings for low speed rated tyres - Class 5 vehicles only

Tyres must be suitable for use up to 70mph (L speed rating) unless the vehicle is a 'restricted speed vehicle'.

If the tyre can carry the maximum permitted axle weight of the vehicle, these vehicles can use tyres with a lower speed rating tyres up to 70mph as follows:

• K speed rating - but the tyre's carrying capacity is reduced by 3%
• J speed rating - but the tyre's carrying capacity is reduced by 7%

For example, K speed rating tyres can be used at 70mph if the load is reduced as follows: 146/143K = 6,000kg single or 10,900kg dual - less 3% = 5,820kg single or 10,580kg dual

You must not accept a tyre load rating that's less than the maximum permitted axle weight.

Structure

Tyres of different types of structure, such as radial-ply and cross-ply, must not be mixed on the same axle.
Steel and fabric radial-ply tyres are considered to be the same structure.

Run flat and conventional tyres can be mixed on the same axle, although this is not recommended.

Condition and fitment

Evidence of a tyre contacting a part of the vehicle, such as due to tyre flexing or suspension movement, is not considered to be a defect. A vehicle should only be rejected if the tyre is fouling a part of the vehicle at the time of test.

Some vehicles have lock stops comprising rubbing pads on the body that the front tyres may contact on a full lock. These are acceptable if they are properly maintained so that they do not damage the tyres.

When assessing cuts in a tyre, it is permissible to check whether a cut is deep enough to reach the ply or cord by using a blunt instrument to open the cut taking care not to cause further damage.

The following criteria should be used when assessing a cut in a tyre:

• any ply or cord that can be seen without touching the tyre - fail
• if by folding back rubber or opening a cut with a blunt instrument, so as not to cause further damage, exposed ply or cord can be seen irrespective of the size of the cut - fail
• if a cut which is more than 25mm or 10% of the section width whichever is the greater, is opened with a blunt instrument and cords can be felt but not seen - fail

Before failing a cut, you must make sure it's the cords that you can feel not a foreign object. If you're not sure, then you should pass and advise.

When assessing lumps or bulges in a radial ply tyre, care should be taken to distinguish between normal undulations in the carcass, resulting from manufacturing, and lumps or bulges caused by structural deterioration.

Take extra care with stretched tyres because they're more prone to sidewall damage.

Recut tyres are only permitted on:

• vehicles over 3,050kg ULW
• goods vehicles with an ULW of at least 2,540kg having at least 16 inch (405mm) diameter wheels
• passenger vehicles with an ULW of at least 2,540kg having 8 or more passenger seats

You should only accept tyres with NHS, Not for Highway Use or similar markings if they have an 'E' marking and a number contained within a circle. Adjacent to this circle, the sidewall must also be marked with a six digit number, which may be preceded by 75R or similar marking (see example below).

Direction of rotation may be indicated by an arrow and/or words, but an arrow by itself should not be taken to indicate direction of rotation.

Asymmetric tyres are marked with correct fitment information on the sidewall, such as 'outside'. However, if an asymmetric tyre is fitted the wrong way around it is not to be considered a reason for rejection. The presenter should be advised.

Tread depth

A tread pattern is the combination of plain surfaces and grooves extending across the breadth of the tread and round the entire circumference. It excludes any tie-bars, tread wear indicators, or features designed to wear out substantially before the remainder of the pattern, and other minor features.

In simple terms, grooves containing tread wear indicators (TWI) or grooves cut as deep as those containing the wear indicators when new, are considered to be primary grooves. Other grooves or sipes that are not cut as deep as the primary grooves are secondary grooves and are not to be considered when assessing tread depth.

The 'breadth of tread' is the part of the tyre which can contact the road under normal conditions of use measured at 90 degrees to the peripheral line of the tread.

Different vehicles require different tread depths.

The following vehicles first used on or after 3 January 1933 need 1.6mm tread depth:

• passenger vehicles with a maximum of 8 passenger seats, excluding the driver's seat
• goods vehicles or dual-purpose vehicles not exceeding 3,500kg DGW
• tricycles with an ULW more than 410kg and all quadricycles

The primary grooves of the tread pattern must be at least 1.6mm deep within the central three-quarters of the breadth of tread and around the entire outer circumference of the tyre (see diagram 1).

Either side of the central three-quarters of the tyre can be devoid of tread ('bald').

Diagram 1. Primary and secondary grooves in tyre tread pattern

The following vehicles must have 1.0mm tread depth:

• vehicles first used before 3 January 1933
• passenger vehicles with more than 8 passenger seats excluding the driver's seat
• tricycles with an ULW not exceeding 410kg with an engine capacity greater than 50cc
• tricycles with an ULW not exceeding 410kg which are electrically powered

The tread pattern must be visible over the whole tread area (see diagram 2), and have a depth of at least 1.0mm throughout a single band of at least three-quarters over any section of the breadth of tread round the entire outer circumference of the tyre.

The 1.0mm tread depth requirement applies to the whole tread width if the original tread pattern did not extend beyond three-quarters of the tyre width when new.

Tricycles with an ULW not exceeding 410kg with an engine capacity not greater than 50cc do not need to have 1mm of tread. However, they must have a visible tread pattern around the entire circumference and across the whole breadth of the tread.

Diagram 2. Tread pattern visibility

Tyre pressure monitoring system (TPMS)

The inspection of the tyre pressure monitoring system (TPMS) is for M1 vehicles first used on or after 1 January 2012.

The TPMS warning lamp (see diagram 3) will generally illuminate and go off again when the ignition is switched on. If the system has identified a previous pressure loss, the lamp will remain illuminated. This does not automatically mean the system has a malfunction. In the event of a system malfunction, the lamp may flash a number of times and then remain on.

Warning messages on dashboard displays are not a defect in their own right, but may assist the tester in determining that the warning lamp is illuminated because a malfunction exists.

If it is unclear the warning lamp is indicating a system malfunction and not a simply indicating that one or more tyre pressures are low, then advisory information should be added to the test result.

Diagram 3. Example of a TPMS warning lamp

Tyre age

The check of tyre age applies to all vehicles with more than 8 passenger seats, other than vehicles of historical interest.

Tyre age is determined by the date code on the sidewall and will be a three or four-digit code. Tyres with a three-digit code will be more than 10 years old.

The code is usually located in a 'window' on the sidewall and may or may not be located at the end of the DOT number (see image below).

The first two digits of the code represent the week of manufacture of the tyre and the second two digits represent the year of manufacture. In the example above, the tyre was manufactured in week 35 of 2016.

Tyres over ten years old at the time of test must be failed if they are on:

• any front steered axle
• any rear axle of a minibus with a single wheel fitment.

Tyres not displaying a date code must also be failed. However, date codes are only required to be marked on one side of the tyre so it may not be possible to see the date code on twin wheel fitments. Under these circumstances you should advise the presenter and assume the date code is present and the tyre age is acceptable.

On tyres where the date code is illegible, for example, due to kerbing or deliberate tampering, a major or minor defect must be recorded, depending on the location of the tyre.

Retreaded tyres

Remoulded/retreaded tyres may have two date codes. One being the original code and the other being the date of retreading. In this case the most recent date code must be used.

The appearance of the date code on retreaded tyres may be different from the original date code and may be branded rather than moulded.

Defect	Category
(a) A tyre: (i) load capacity or speed rating not in accordance with the minimum requirements (ii) load capacity insufficient for axle presented weight	Major Dangerous
(b) Tyres on the same axle or on twin wheels are different sizes	Major
(c) Tyres on the same axle of different structure	Major
(d) A tyre: (i) with a cut in excess of the requirements deep enough to reach the ply or cords (ii) with a lump, bulge or tear caused by separation or partial failure of its structure, including any lifting of the tread rubber or with cords exposed or damaged	Major Dangerous
(e) Tyre tread depth not in accordance with the requirements	Dangerous
(f) A tyre fouling a part of the vehicle	Major
(g) A recut tyre fitted to a vehicle not permitted to be fitted with recut tyres	Major
(h) Tyre pressure monitoring system malfunctioning or obviously not working	Major
(i) A tyre not fitted in compliance with the manufacturer's sidewall instructions	Major
(j) A tyre valve seriously damaged or misaligned likely to cause sudden deflation of the tyre	Dangerous
(k) A tyre incorrectly seated on the wheel rim	Major
(l) Tyre obviously under-inflated	Minor
(m) A tyre over ten years old is fitted to a front steered axle of a bus, coach, or any axle on a minibus with a single wheel fitment	Dangerous
(n) A date code illegible: (i) on a tyre fitted to a rear axle of a bus or coach (ii) or not visible on a tyre fitted to a front steered axle of a bus or coach or any axle on a minibus with a single wheel fitment	Minor Major

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