How to protect wheels and prevent wheel detachment

How to protect
wheels and prevent
wheel detachment
November 2015
HOW TO PROTECT WHEELS
& PREVENT WHEEL DETACHMENT
The term ‘wheel detachment’, favoured by
engineers, is a clinical description and a bit
of 10 tons is the stuff of disaster movies and motorists’
of an understatement.
unaware for minutes or even hours that a wheel has separated.
The image of wheel nuts spinning or shearing away and the wheel
avoided through consistent appropriate maintenance. But the
flying off a vehicle or trailer, accelerating up to 150km/h (93mph),
figures show that wheel detachment continues to be an issue in
bouncing up to 50m high, and impacting other vehicles at a force
the transport industry.
nightmares. With heavy truck trailers, the driver can be
Any ensuing damage and injury would have been easily
The Statistics
Wheel detachment is a global problem; one dramatic story is
detailed on a Canadian newspaper’s website, along with a list of
3-7
3-7 fatal accidents occur due to
wheel fixing defects each year.
such incidents over the years. The role of wheel fitters and drivers
is key in avoiding such an accident. According to the authoritative,
much-quoted study by the Transport Research Laboratory (TRL) in
2006, 3-7 fatal accidents occur due to wheel fixing defects each
year. Up to 27 people are injured, while up to 134 drivers have to
contend with accident damage. It’s worth noting that these figures
do not tell the full story. Cases of wheel loss that do not involve
27
134
Up to 27 people
are injured.
Up to 134 drivers have to
contend with accident damage.
injury or damage aren’t necessarily recorded, so are ‘below the
radar’. While it’s generally agreed that accidents related to wheel
loss are comparatively rare, up to 11,000 wheel fixing defects are
estimated to occur each year.
How to protect wheels and prevent wheel detachment www.wheelsentry.com
11K
Up to 11,000 wheel fixing defects
are estimated to occur each year.
02
THE COSTS OF DEFECTIVE WHEEL
FIXINGS & WHEEL LOSS
Wheel fixing defects can have consequences for
the driver and fleet operator. These include:
Compliance
Compensation
Operator Compliance Risk Score (OCRS) Drivers are
If wheel loss results in an accident involving other
stopped at the roadside by the police or the Driver
vehicles, the driver or operator may be liable for
and Vehicle Standards Agency (DVSA) for vehicle
vehicle damage and bodily injury, through claims
inspections. The DVSA uses the Operator Compliance
brought by those seeking financial compensation for
Risk Score (OCRS) system to decide which vehicles
physical, emotional, and/or financial losses resulting
should be inspected. As an operator you get
from the accident. For example, vehicle accidents
points when a test or inspection finds a defect or
are known to cause post-traumatic stress syndrome.
infringement of the rules. The more serious the defect
According to Kevin Bolton, a solicitor and accident
or infringement, the more points. The scores are R (red
injury expert, a minor case of post-traumatic stress
- highest risk), A (amber - medium risk) and G (green
syndrome can be awarded £2,800- £6,000. This
- lowest risk). The OCRS is used to calculate the risk of
is increased up to £17,000 for ongoing symptoms.
an operator not following the rules on roadworthiness
A severely disabling case could be awarded up to
(the condition of its vehicles) and traffic, eg drivers’
£72,000. For further details on compensation that
hours, weighing checks.
could be claimed, click here.
Penalties
Police officers and inspectors from the Driver and
Vehicle Standards Agency issue graduated fixed
penalty notices for roadworthiness offences such as
defective wheels and fixings, and may also prohibit
the driving of the vehicle on a road. The culpability
of the driver in respect of vehicle defects is the main
consideration in the issuing of a fixed penalty notice.
How to protect wheels and prevent wheel detachment www.wheelsentry.com
03
A HOLISTIC APPROACH
COVERS ALL BASES
From the discussions on the truckers’ website
TruckNet UK, it’s clear that the issue of
managing wheel nuts can be problematic,
with drivers seeking guidance on how to
maintain their wheels.
the freight interests of business in the UK. Its 14,000 members
range from small and medium-sized businesses to multinational
companies involved in operating across modes of transport,
including 200,000 heavy goods vehicles. The IRTE supports
transport engineers and encourages high standards, with an
emphasis on safety and best practice.
In the introduction to this guide, Phillip Brown, then senior traffic
commissioner, emphasised a holistic approach to wheel security.
‘While there are products on the market that can make wheel
nut movement more noticeable, or prevent wheel nut movement,
operators cannot “fit and forget”. A good maintenance regime
which is underpinned by routine preventative measures, as part
of driver walk-round checks, is essential, as are well-understood
Don’t check
procedures for fitting wheels.’
Mark Forster, fleet compliance and audit manager for Sita UK,
emphasises this point too, in an article for Transport Engineer:
‘For an organisation to reduce the likelihood of wheel loss, it
In the TRL survey 32% of drivers admitted they didn’t check
is important that it has in place a clearly defined wheel security
for loose wheel nuts.
procedure that has been comprehensively publicised to its drivers
and service providers. It is also essential that all relevant personnel
For safety on the road, drivers need to understand the ins and outs
play their part in strictly adhering to that procedure.)
of wheel security, from the dangers of using an air-gun on wheel
nuts, to the interference of dirt. Given that trucks and trailers need
to be in excellent working order to perform well in demanding
conditions, and that considerable maintenance of the wheels is
needed for this, it’s important that this is made simple and easy to
do. The adoption of a standard method of wheel checking and
fitment, requisite training and compliance by drivers and fitters
would avoid the problems of wheel fixing defects.
In 2009, a best-practice guide to Wheel Security was produced
“...it is important that
it has in place a clearly
defined wheel security
procedure”
by the Freight Transport Association (FTA), the Institute of Road
Transport Engineers (IRTE), and SITA UK. The FTA represents
How to protect wheels and prevent wheel detachment www.wheelsentry.com
04
WHAT HAPPENS WHEN
A WHEEL DETACHES
According to American firm MEA Forensic Engineers & Scientists:
roadway, where its inconspicuousness can make it difficult to avoid.)
‘When a wheel separation occurs on a motorway, the separated
The approach speed between the now bouncing projectile and
wheel is launched high in the air - because the weight of the vehicle
oncoming vehicles can easily exceed 160km/h (100mph). The
pushing down on it is suddenly removed - yet is hardly slowed
injury potential resides in the escaped wheel’s ability to penetrate an
down. (In some cases a separated wheel comes to rest on the
oncoming vehicle and strike occupants directly.’
What causes wheel fixings to loosen
The wheel design is affected by large amounts of degradation of the components, and/or
imperfect maintenance procedures, which leads to insufficient clamping force. This can lead to
movement where the wheel and hub meet, causing wear and loss of stud/bolt tension
The FTA and IRTE identified the following causes:
• The fixing is insufficiently tightened and allows the wheel to wear
• Worn wheel spigots
• The fixing is over-tightened, causing stretched/broken studs
• Fractured or seized wheel nuts washers
or causing studs to be pulled through the hub. Drivers and
maintenance staff may over-torque wheels to try to prevent them
from coming loose. This will result in stud failure as the elastic
limit of the material is exceeded
• Failure to regularly check the tightness of wheel fasteners
• Fitment of incompatible or unserviceable wheels and components
• Incorrect lubrication of threads and interfaces. Lack of initial
clamping force can be due to high friction loss.
• Excessive lubrication or incorrect lubrication, eg applied to the
mating surfaces of wheels.
• Brake drum securing screws/bolts loose, holding wheel off the
hub face
• Inaccurately calibrated torque wrench or calibration date expired
• Incorrect use of air impact tools. This is a common cause of both
under-torqueing and over-torqueing because the actual torque
depends on a wide range of variables and is not measurable
• Incorrect tightening sequence
• Temperature effects. The clamp load can vary during service due
to changes in temperature of the components
• Settlement from any other factor eventually causing the
• Severe corrosion and/or wasting of wheel studs
clamping load to become inadequate. The assembly can only
• Studs not pressed fully into the hub or loose back nuts
accommodate a very small amount of settlement. The wheel
• Incorrect assembly, eg not following the correct torque and
studs are very stiff and the amount of extension caused by the
re-torque procedure
• Paint, rust/scale or dirt on mating surfaces
How to protect wheels and prevent wheel detachment www.wheelsentry.com
tightening torque is limited, particularly if the stud tension is lower
than intended in the first place. Nut movement can be indicated,
whereas settlement is difficult to detect visually.
05
A COMMON CULPRIT
Air-impact tools, also known as air-guns, are easily misused.
irrelevant after the nuts have been over-tightened with an air-gun,’
According to Paul Rea, owner of a New Zealand company
says Rea. ‘They’ve been over-torqued and when the setting’s
supplying wheel-nut indicators to the heavy transport sector, impact
checked with the torque wrench, it obviously passes easily. But the
tools are by far the greatest culprit of wheel fixing defects. ‘Tyre
damage has been done – the studs are stretched.’
and wheel-fitters use an air-gun in the interest of getting the job
done quickly and minimising a vehicle’s downtime – and that’s
understandable. But problems arise when the air-gun is overused –
the nuts are over-tightened, stretching the studs and/or damaging
the threads,’ says Rea. ‘The clamp force – between wheel and hub
– is immediately compromised, affecting the integrity of the unit,
and potentially leading to a wheel detachment. The only solution
is to replace the studs – and it will hopefully be done before a
detachment occurs.’
Vehicle manufacturers specify the torque setting for wheel nuts
which should be tightened and checked with a torque wrench. (See
“...problems arise when
the air-gun is overused
– the nuts are overtightened, stretching the
studs and/or damaging
the threads.”
The Re-torque Procedure, below.) ‘But the torque wrench is often
How to protect wheels and prevent wheel detachment www.wheelsentry.com
06
DRIVER CHECKS
As part of their pre-use checks, drivers must carry out a visual inspection of the
vehicle wheels for security. Any defects including loose wheel nuts should be reported
immediately and the defect investigated – the wheel removed and the components
examined and rectified by a competent person.
Drivers should check wheels for:
Driver training should include:
• The position of wheel nut indicator devices (if fitted),
• How to set and use a torque wrench correctly
which show whether wheel nuts have moved
• Signs of damage to nuts and studs
• Cracked wheels, nuts, washers
• Missing, broken or loose fixings/components
• Distorted rims
• Elongation of stud holes
• Signs of wheel looseness. If so, check the wheel nuts
with a calibrated torque wrench (see The Re-torque
Procedure, overleaf)
• The correct torque setting for the vehicle type and model
(as per manufacturer’s recommendations)
• Why it’s critical that wheel nuts are subject to an initial torque
and re-torque
• Why it’s important to stop applying pressure once the torque
wrench has reached the required setting
• Signs to check for (see list above)
• How to reset the torque wrench to zero once it has
been used
• Bright metal in the area of nut and washer seating
• Rust that can be seen radiating out from the area
of the nut and washer
• Blocked ventilation holes
How to protect wheels and prevent wheel detachment www.wheelsentry.com
07
THE RE-TORQUE
PROCEDURE
When the clamping force reduces, the tension
needs to be restored through re-torqueing the
wheel nuts. Manufacturers specify the torque
required for their product. If a driver or fitter
doesn’t follow these instructions, the wheel nuts
are compromised.
‘The proper torque stretches the bolt. Stretching is what allows the
threads of the stud/bolt to tightly mate and secure to the counterpart nut or threaded hole (the axle or wheel mounting hub) without
working themselves loose,’ he says. ‘It’s almost like mechanically
welding the nut to the bolt – except that you can remove and
retighten it repeatedly.’
Referring to this diagram, Miller explains further:The first example
The Applied Auto Weblog by Jack Miller in the US, an automotive
is a bolt that is loose and no torque applied – unstretched. The
product engineer and technical trend analyst, details how to torque
second example is a bolt that is torqued to spec. There is a
‘lug nuts’ (American for wheel nuts) clearly, and includes the
slight amount of stretch, but not enough to change metal/alloy
diagram featured below.
properties of the bolt – thus returning back to its original shape for
re-tightening. The third bolt example is a typical over-torqued bolt.
Note that the bolt is not only stretched, but stretched to the point of
changing the properties and ‘yield strength’ of the bolt. The bolt
now has a much lower tensile/yield strength and allows the bolt to
flex, generate heat and fatigue – thus cracking, shearing, loosening
and breaking off result, causing damage to the wheel and other
related components.
Un-Torqued
Torqued to spec.
Over-Torqued
A helpful resource is Popular Mechanics, which includes a ‘Torque
101’ article on the technicalities and torque wrench basics, here.
The vehicle maintenance news and information
resource Vehicle Service Pros points out that the
torque wrench manufacturer’s instructions for
keeping the wrench calibrated should
be followed.
Maxion Wheels
How to protect wheels and prevent wheel detachment www.wheelsentry.com
For more information visit
www.vehicleservicepros.com/tire-wheel
08
THE ’30-MINUTE
TORQUE PROCEDURE’
Some guides advise that following a wheel fitting, the wheel nuts must be rechecked
for tightness after the vehicle has stood for a period of 30 minutes, whether the vehicle
has moved or not, or after 40-80 kilometres using a calibrated torque wrench set to the
manufacturer’s specified torque value. However, some vehicle manufacturers do not
recognise the 30 minute-torque procedure. It is best therefore always to refer to your
specific vehicle manufacturer instructions.
Re-torque dos and don’ts
Following a wheel fitment:
• Don’t simply slacken and retighten the nuts.
• Do the re-torque before the vehicle is put back into service. This
• Do simply check to see if the correct torque is still applied/
tightened to the correct torque. Wheel nut indicators such as
Wheel Sentry® enable you to easily check for movement.
• Do tighten any loosened nuts to the specified torque using
a calibrated torque wrench when the wheels are cold.
• Do complete a ‘re-torque label’ – common practice across
may require a short road test of the vehicle. If, however, this
is impractical then the 30-minute procedure (above) applies.
Alternatively, inform the driver that the re-torque procedure
is required and that the wheel nuts need to be rechecked for
tightness after either 30 minutes or after the vehicle has travelled
40 to 80km. Always refer to the vehicle manufacturer instructions
regarding when and how to re-torque.
the industry - to ensure wheel nuts are always subject to an
initial torque and re-torque. This will form part of the vehicle’s
maintenance history, and should include instructions to tyre
fitters/workshop technicians and drivers.
Planning for safety on the road
The DVSA report for 2011/2012 shows that over a third of
roadworthiness checks resulted in prohibitions. The figures
for 2009/2010 are similar, followed by a small decrease in
2010/2011. The question is, will the situation improve? With the
appropriate training and equipment, and a defined wheel security
“...over a third of
roadworthiness checks
resulted in prohibitions.”
procedure, every driver and operator is able to do their part to
impact these statistics, and minimise wheel-fixing defects and
wheel detachment.
How to protect wheels and prevent wheel detachment www.wheelsentry.com
09
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