Road and workshop
Page 30
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by Handyman
Manpower, maintenance and the MoT (23)
• The subject of tyre failures and their causes could almost become an exercise on its own during the tuition of a new driver. It has been proved time and time again that to neglect passing on vital information on tyre defects is to invite
a real session on the subject laterwith the cost of the first lesson in the
region of £30.
It is a wasted exercise to wait and show the driver the tyre that he himself has unwittingly ruined when it is so easy to show him one from some earlier incident. There is no need for long drawn discussions, the best answer is the sectioned tyre clearly showing the trouble and its cause and six sections of damaged tyres will cover the subject amply.
We have already spoken of the tyre cracked or ripped at the outer tread, caused by mounting a kerb fully laden. And we know about the tyre that wears rapidly through out-of-track running, due to a bent track rod or steering arm. Now we will look at another,aspect.
Often there is quite a lot of argument after some ditching incident which included a blow-out. In certain instances the driver may have been uncertain of his facts or misguided enough to say the tyre burst of its own accord and put him in the ditch. But when the burst casing is opened there is the X fracture that is always in evidence in instances of concussion burst in the tread area. This at once reverses any suggestion that the tyre burst for other reasons. It means that the ditching occurred first, followed by severe impact with a very solid object.
It is true though, that an ordinary builder's brick hit at high speed can cause the same effect, though the brick has to be struck absolutely square on, a very rare happening indeed.
The tyre that has been run in a flat condition speaks for itself once opened by the tyre spreaders. The action of running flat eventually causes destruction on the inside wall—the appearance inside is a mass of loose strands.
In a much earlier article I referred to the brick, stone, or metal debris trapped between twin tyres and of the immediate need to release this before it could carve into both tyre side walls and destroy both tyres. • Here the best answer is certainly not the quick one of belting the trapped material with heavy hammer or crowbar blows, hoping it will break up or dislodge. There is little hope of achieving this, at least not without a grave risk of cutting the tyre walls.
If the debris is securely wedged between the tyres, the proper approach is to jack up and slacken off the wheels and let the debris drop out. It also pays to inspect the scarred area for depth of penetration before running on.
A much more difficult fault to spot, unless the damage is severe, is where some part of a mudguard, body bolt or spring slip bolt is in contact with a tyre, or can be when loaded. In this condition where a vehicle is running on an undulating road contact of only a few seconds at wide intervals can carve a tyre to destruction.
Whilst these faults are usually noted at service periods, Where a weak spring may be the cause, things can happen when in the hands of the driver with the same end result. For example, recently a driver when reversing to unload on a building site and using full lock both ways caught the lower corner of his rear steel wing, bending the valance inwards towards the tyre. but not in actual contact with the tyre. The wing on this motive unit was quite strong ,and set low at the rear below axle centre and as the weight came off the vehicle the bent wing edge made contact with the tyre treads and was pulled into tighter contact as the wheel revolved.
The result was a machined groove through the tread and into the casing— total destruction. The way to avoid this type of mishap is, of course, use of rubber mudflaps. But manyusers of Scammell hitch chassis, for instance, still set a steel wing at ten minutes to and twenty past as in the case I described.
In the same way an overload can bring a mudguard bolt, body bolt or even a rope hook into a position where intermittent contact is likely with the tyre on rough roads. The main point is to highlight the damage and its cause and to emphasise the value of a look round both tyres and vehicle after manoeuvring on restricted or congested sites.