It's been around
a year since the new Express highway between Mumbai and Pune has been opened
for a small stretch. This vision of future has given most motorists a taste
of speed, which one could only dream of, in our country. Yet with this limited
access a lot of people have been asking me the same question - "Are our
tyres safe enough for such roads?" When answered in affirmative, invariably
the next question is, "Then why are the tyres failing on these roads?" The
majority of the tyres which I have personally seen, have been subject to
negligence, abuse, or age problems.
Many people treat tyres as a necessary evil, filled with problems like punctures,
cuts, wobbles, unstable and fast wear. Most motorists fail to check the
correct air pressure, and if they do it's the 'chokra' at the petrol pump
who dictates the correct pressure for use. I have seen very few persons
who are actually interested to see that their tyres are correctly inflated.
The same goes for the alignment or wheel balancing. People tend to forget
that it's a small patch of rubber about the size of a footprint which forms
the thin line between safety and disaster, yet when a tyre fails or a time
for replacement comes they find that this is an expensive proposition to
be dealt with. Expensive when compared to one's life?
Tyres have come a long way since the times of the 'mummified' tyre of Dunlop.
Even the technology about 35 year's back during my training has undergone
a drastic change. The prime concern of a manufacturer, during build-up of
a tyre is uniformity. But in those days we commonly found it a bit difficult
to make tyres truly round and which ran truly straight, thus uniformity
meant a proper dimensional and geometrical congruity. We had to ensure that
the joints were correctly placed. The carcass was rayon with nylon just
being introduced, thus making a tyre vulnerable to problems like casing
break up or CBU. Times have changed and today most service engineers are
not concerned about such defects since they have been eliminated. Nowadays
uniformity stands for material uniformity, uniformity in production, less
defects during production, which is termed as zero defects. Tyre manufacturers
are more concerned about safety, lower noise level, and better traction.
To many a tyre is still made of 'rubber' and therefore is not really any
different. Where the basic material of older generation tyres was natural
rubber, a modern passenger car tyre may contain only 10 per cent of it along
with 25-30 different materials, which in turn are made up of hundreds of
different chemicals. This fact can be really surprising when you consider
that some materials are considered contaminants and are incompatible with
other material. Yet the tyre manufacturer has combined such materials working
in harmony to deliver an improved air retention and blow out resistance
giving safer tyres.
A quick look at the advancements in tyre during the past years can be very
instructive. From the 'straight side' tyres of 1924, to the 'balloons' of
1930s, the cross ply tyre of today has not changed much with regards its
construction. The change has been when compared with the longevity, ride
comfort, and carrying capacity of the tyres. But a break in technology in
its true sense has been the introduction of radials in 1948 by Michelins.
Even the tyre, introduced by Michelin's chief engineer Pierre Bourdon, and
Francois Michelin's uncle, was crude when compared with the tyres of today.
Their basic idea was to separate as far practically possible some of the
factors controlling the basic requirements of the tyre from factors affecting
structural stiffness in the ground contact area, which influence cornering
control properties and rate of tread distortion and abrasions.
Once tyre manufacturers were able to realise that such ability was possible,
it was only a matter of time before they produced tyres as per requirements
of individual car owners. Another vital improvement, which played a significant
role in the industries, was the use of tyres as a part of the suspension
system for the vehicles. This led to marking of the speed code for tyres.
Thus 'S' stood for standard speed (180kmph), 'H' for high speed (230kmph),
while 'V' for very high speed (above 230kmph). As tyre compounds depend
upon the speed the tyres are used, today we have a range of alphabets to
describe the speed codes for tyres. An addition to this marking has been
the load index, which signifies the actual load the tyre is capable of carrying.
This brings up the question again as to why do tyres fail on the Expressway.
I have tried to analyse some of the tyres, which we have received and would
like to present some of these cases to you.
Another peculiar aspect I have noticed is that most of the tyre problems
have occurred on vehicle during the Pune to Mumbai stretch and not during
the Mumbai-Pune one. This could be due to the fact that the 65km stretch
starts first, followed by the ghat where the use of brakes are more, causing
heat buildup then is followed by the 22km stretch. Therefore my conclusion
is before your journey check your tyres for correct inflation pressure,
see that no stone chips or nails are on the tread, check for slow leaks
such as a leaky valve pin, ensure that the dust caps are fitted to the valves,
try to drive your vehicle at the permissible allowance your tyres are marked,
or in case you want to always drive faster change to a higher speed rating.
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March 2001