DIRECTORATE GENERAL BORDER ROADS
GENERAL MAINTANENCE INSTRUCTION NO: 165
ON
PNEUMATIC TYRES AND TUBES LIFE
Aim:- The aim of the instruction is to guide the user units to achieve maximum utilization of pneumatic tyres and tubes and Field Repair Workshops for proper conditioning.
General:
1. Reference this Directorate letter No. 67721 / DGBR/ E4T
dated 19 Nov 71. Appendix “A” Page 5.
2. Tyre life has been laid down as 24000 Kms for new tyres
and 16000 Kms for retreated tyres as per the above cited reference only as a
guide for Field Workshops for sentencing the tyres to BLR/BER.
Para 2 (I):- The life of Tyres of various
sizes of JCB Excavator and BEML Pay Loader for sentencing them to BER is hereby
fixed as under:-
Sl No
|
Make &Type
|
Size of Tyre
|
Life Fixed
|
Remarks
|
01
|
JCB Excavator
|
a) Rear wheel
14.00 x 25
|
2000 Hrs
|
|
b) Front wheel
9.00 x 16
|
1000 Hrs
|
|||
02
|
BEML Pay Loader
Cum Wheel dozer 1420Z/ 1420L
|
18.00 x 25
|
3000 Hrs
|
Para 2 (II):- The life of tyres of Bomang
Vibratory Road Roller for sentencing BER is fixed as under
Sl
No
|
Make & Type
|
Size of tyre
|
Life fixed
|
Remarks
|
1
|
Bomang vibratory Road Roller
|
23.1 x 26
|
2000 Hrs
|
As
per amendment to GMI 165 vide HQ DGBR letter No 55021/TI/ DGBR/89 /E4 tech
dated 15 Sep 2005.
Para 2 (III):- The life in respect of Snow
cutter for sentencing them to BER is fixed as under:-
Sl No
|
Make &Type
|
Life Fixed
|
01
|
Schmidt Snow Cutter
|
2000 Hrs
|
02
|
Steyr Snow Cutter
|
1500 Hrs Front Tyre
|
2000 Rear Tyre
|
As
per amendment to GMI 165 vide HQ DGBR letter No 55014/Policy/DGBR/164/ E4 Tech
dated 27 May 2013.
Para 2 (IV):- The life of tyre of Skid
Steer Loader for sentencing them to BER is fixed as under:-
Sl No
|
Make & Type
|
Size of Tyre
|
Life Fixed
|
01
|
Skid Steer Loader
|
1200 x 16.50
|
1000 Hrs
|
3. The above stipulated life of tyres can be
expected only when the vehicles with proper load and correct steering geometry
are plying on good / tarmac road in the plains. Besides, good maintenance of
tyre is correct air pressure, careful driving and timely action to rotate tyres
will enhance tyre lives. In BRO, most of our vehicles run on hilly uneven roads
and carry awkward loads like stones and barrels.
4. The
purpose of this instruction is to acquaint the operator with the principles of
tyre care and recommend to him what he may do by way of efficient tyre
maintenance to reduce the operating costs.
5. Even
operator should choose tyre with due care, fit the correct ones for the
conditions of service, fir them in the right position, check service
conditions, maintain chassis, and more than anything else organize a proper tyre
maintenance service. If all things are done, a definite cost benefit will
accrue in all the projects.
6. It is
needles to assert that tyres are an expensive item in the cost budget of any
transport undertaking, but all too frequently they are virtually ignored from
the time of initial fitment until the time of ultimate failure and as result
millions of potential tyre KMs are wasted each year. The road conditions and
tyre of service play a big part in determining tyre life, but most of the factors
under these headings are usually beyond the control of individual operator.
There is, however very important factor influencing tyre which is under the
direct control of the operator. These factor is efficient maintenance, and its
implementation can bring about a substantial reduction in tyre cost per KM. A
modest increase of 5% in tyre mileage will represent a considerable saving in
the yearly operating costs of even a small fleet actually achieved by the
implementation of a simple, but efficient, tyre maintenance system.
7. Appendix
“A” to this letter gives the essential information about tyres and tubes.
8. OC
Workshop must be familiar with the road conditions, climatic and terrain
effects, and the loads carried by the vehicle. OC Workshop is the right person
to decide about the conditions and causes of failure of tyres for BLR/ BER. In
all cases whether the tyre has achieved the stipulated life or not, OC Workshop
should record to clearly whether the tyre has failed due to fair wear and tear
or due to unfair wear and tear. Where a particular tyre yields lower life than
other tyres used on similar tyre of vehicles deployed on similar duties under
similar operating conditions, OC Workshop should use his technical judgment
while declaring it BLR / BER due to fair / unfair wear and tear.
APPENDIX “A’ TO GMI
NO. 165
ESSENTIAL INFORMATION
ABOUT TYRES AND TUBES
1. What
is Pneumatic tyre? It
is an air bag fitted to a road wheel. It consists of two main components the
outer tyre or cover and the inner tube, both of which are mounted on a rim, the
complete assembly forming an effective compressed air container, and the “AIR
CARRIES THE LOAD”.
2. The
tube The tube is constructed so as to prevent the loss of
compressed air and, at the same time be as flexible as possible. The cover is
protection for the tube and has to be strong enough to restrain the compressed
air in the tube and protect it from damages. At the same time, it has to be
pliable enough to withstand continual flexing by the rotation of the tyre under
load.
3. What
does the tyre do The tyre provide a cushion between the vehicle and the
road thus eliminating road shock and damping down vibrations, it is transmits
the power from the engine through the medium of the driving wheels to the road.
When the brakes are applied, it is tyre again which transmits the whole of the retarding
force. In order to give the maximum grip on the road surface a tyre is provided
with a tread pattern and various designs of tread patterns are available to
give the best performance for different conditions of operation.
Every
tyre is for its particular job. “It has a maximum load carrying capacity for a
given recommended inflation pressure, and to obtain the performance with the
minimum of cost it is desirable that theses and inflation pressures are not
exceeded”.
Remember that the “AIR CARRIES THE
LOAD”.
4. Tyre
Deflection Each type and size of tyre is designed to
deflect at a predetermined percentage when under a given a load and inflated
with the specified air pressure. The correct deflection result in the proper
contact of the tread area with the road surface. Proper deflection is vital for
satisfactory tyre performance over load or incorrect air pressure increases or
decreased the tyre deflection and road contact area of the tread.
The tyre designers have established
for each tyre and size of tyre, the correct air pressure for various loads that
all tyre should carry, up to maximum load for which each tyre is designed. By
maintaining the correct air pressure applying to specified loads, the tyre
deflection and tread contact area for which the tyre is designed remain
constant.
5. Under
Inflation Under inflation is one of the destructive
factor that enters into the performance of a tyre, and it is surprising how
many operators give this important matter little consideration. A tyre is not
properly inflated unless the air pressure is sufficient to support the load
without excessive defection and maintain the tyre beads in correct position on
the rim under the conditions.
When a tyre is operated without
sufficient air pressure, the side walls are subjected to executive flexing and
in each revolution the wheel side walls are forced to bend and recover to an
excessive degree. The abnormal flexing action will result in breakdown of the
structure, with the result that the tyre is weakened in this area and is unable
to withstand ordinary road shocks. The individuals cares will became loose and
break and in addition ply or tread separation may result under inflation is
also the cause of rapid and uneven tread wear
resulting in thousands of lost kilometers.
6. How
to prevent costly under inflation failure
a)
|
Make sure that tyres are
inflated to the recommended pressure. Check regularly.
|
b)
|
Ensure that valve caps
are kept screwed on tightly
|
c)
|
Check for slow leaks
whenever air pressure shows a decided drop.
|
d)
|
Main blow leaks repaired
immediately
|
Always remember that, tyres are costly whilst
air is free.
7. Over
inflation There is
a mistaken conception on the part of many operators that a tyre can be
overloaded safely by over inflating. This is a very dangerous practice.
Increasing air pressure to off set over loading simply distorts and strains the
cord plies of the tyre beyond their capacity, eventually weakening the entire
structure and terminating in premature failure. Over inflation promotes danger
of bruising or concussion and cutting since it put both car cases and tread
under greater tension which increases the case with which either or bruises
occurs. Over inflation causes fast tread wear in the center of tread due to
decreases in road contact area and thus resulting in load per square inch.
It
must be also remembered that over inflation reduces traction and skid
resistance, because of the similar tread area in contact with the road surface.
For this reason over inflated tyres are particularly dangerous on wet roads.
Over inflation also gives harder riding, due to the fact that the tyre
cushioning effect if greatly reduced, apart from discomfort this will result in
higher vehicle maintenance costs.
8. Over
loading A large proportion of the premature tyre failures experienced are
due to over loading. Every tyre, regard less of its type, is designed to carry a specific load at
a specific inflation pressure and this load is the maximum the tyre can carry
on the basis of 100 % performance and kilometers. If the load per tyre is in
excess of the maximum specified limit then the kilometers given by the tyre
will vary proportionately.
9. Bleeding
Tyre
bleeding is the practice of letting air out of tyres when inflation pressure
builds up due to the heat of the operation. The procedure is wrong. It has been
proved that such a practice causes even greater increase in tyre temperatures
resulting in premature failures also operators may forget to re-inflate their
tyres after vehicle has been standing overnight and consequently tyre failure
occurs due to gross inflation. If these are not bled equilibrium is reached between
heat generated by the tyre flexing and heat dissipation, so that the
temperature of the tyre remains constant. The bleeding of tyre reduces the tyre
pressure, but not the temperature of a tyre. When tyres are bled, the flexing
of the tyre side walls I increased, thus causing higher tyre temperatures than
would have been reached if the inflation pressure had not been reduced.
Excessive heated results in faster tread wear and increased danger o heat blot
outs.
10. The effect of Heat Excessive
heat is generated by the abnormal flexing of a tyre due to overload or under
inflation, and is aggravated by sustained high speed operation. High
atmospheric temperatures will also further aggravate the position.
11. The effect of heat tyre fabric The ten side strength of the fabric
cords in the tyre casing is reduced when the casing is subjected to high
temperature. At the same time the high temperatures cause the air in the tube
to expand and this subjects the already weakened tyre cord to increased strain.
Under these conditions the tyre is more prove to injury as the result of
impacts.
12. The effect of heat on tyre casing rubber
compound Extreme
heat is highly destructive to the rubber compounds used in the casing of tyre
and will almost certainly cause premature looseness failures.
13. The effect of heat on tread wear:- Under the effects of extreme heat the
abrasion resistance of the tread rubber compound is greatly reduced. When
subjected to high temperature the tread rubber softens and therefore wears more
rapidly resulting in decrease in tread life.
14. The effect of speed High
speed in increased tyre temperature and it is the experience of most operators
that the faster one drives over any particular kind of surface the more rapid
is the rate of wear of the tyre tread. However, the inter relation of increased
wear of tyre treads with increase of speed from 56 to 72 Kms per hour reduces
tread life by 22 % while a further increase to 80 Kms per hour reduces tread
life to 33 %.
15. Road conditions The
life of a tyre is greatly affected by the type of road on which it runs, and it
requires very little thought to appreciate that there is a vast difference
between the abrasive action of a bone dry, flinty or “ Kankar “ surface, and
that of a wet smooth bitumen road.
Tyre
that run for their whole life on good earth on gravel roads can only be
expected to render about 60% of Kms that they would have given on smooth,
level, well paved roads.
If
used on fresh cut roads, the life of the tyres will be only 50 % of the normal.
Again
on very hilly roads, even where the road surface is good, the tread life will
only be approximately 50 % of the normal so that on hilly twisting roads with
poor surfaces, speeds and loads must receive special attention, if very short
tyre life is to be avoided.
It
must always be remembered that on any road the service rendered by a tyre is
largely in the hands of the driver and indeed the driver is most important man
in any consideration of tyres performances. Such things as the severity of acceleration
of braking, speed and a watchful eye for put holes or other obstacles are
wholly with in the drivers controls. It also follows that inspection of tyres
and for that matter, of the whole vehicle by the driver at regular intervals
will catch small troubles before they become big.
(Note:- These
percentage lives apply only to manufactures estimate of tyre life.)
16. Vehicle mechanical irregularities If
tyres wear irregularly, or more rapidly than expected, it may be that vehicle
mechanical irregularities are responsible. The following are some of the wheel
or vehicle irregularities which may cause rapid or uneven tyre tread wear.
17. Wheel misalignment It is very important
that correct wheel alignment, according to the vehicle manufactures specification,
should be maintained. Whilst this mainly applies to front wheel, it is also
applicable to rear wheels in special circumstances.
A
wheel 6.4 mm approximately out of alignment is dragged sideways appx 15 Mtrs in
every Km and the result is very rapid tread wear. Measurement of alignment is
taken by means of an alignment gauge.
The
distance is measured between the tyres at the opposite ends of the same axle.
If the distance at the front of the tyre is less than that taken at the back,
this is known as “TOE – IN”.
If
the distance is greater at the front of the tyres than at the back, then it is
known as “TOE – OUT”.
18. Excessive wheel camber Camber
is the angle by which the wheels are inclined from the vertical. When the top
of the tyre is inclined away from the chassis member, that is further from the
frame, than the bottom of the tyre, then this is known as positive camber. If
the top of the tyre is inclined towards the chassis member than it is known as
negative camber.
In
the case of twin tyres excessive camber may be due to a bent or sagging axle.
This results in over leading of the inner tyres, which in addition to
increasing the rate of tread wear on the shoulder of the tyre may also lead to
premature failure of tyre. Exactly the same tread wear effect may be observed
in tyres operated over heavily cambered roads and for this reason the use of
differential inflation pressures might be advisable. Excessive camber may also
due to excessive wear in the front end bearing or incorrect king pin
inclination.
19. Badly adjusted or grabbing brakes Brakes out of adjustment and out of round
brake drums cause rapid wear in a single spot.
Improperly
adjusted brakes generally produce several spots on the tyre.
a)
|
Loose steering linkage
|
b)
|
Worn wheel bearings.
|
c)
|
Spring or twisted frame.
|
d)
|
Wobbly wheels.
|
All the above will result in uneven
and irregular tyre tread wear.
20.
TUBES
a)
|
A
tyre is not better than its tube The pneumatic tyre and the vehicle it
carries are supported by air confined within the tube and not by the rubber
and fabric by the tyre. This is clearly demonstrated when a tyre is run
without air. Since the tube holds the air, the importance of the part the
tube plays in the satisfactory performance of the tyre is readily apparent.
|
|
b)
|
How
to get good service from tubes The long life and high Kms given in present
day tyres exhaust the useful service life of tubes. Therefore, when a tyre
cover is worn to the point of being no linger serviceable the tube also is generally
in an unserviceable condition and it should be replaced with a new one.
|
|
c)
|
Always
fit a new tube with a new cover. Never
use a tube in tyre cover of a size larger than that for which the tube was
designed. The use of an under size tube results in:-
|
|
i)
|
Excessive
stretching of the tube, which thins the tube walls, causing abnormal loose of
air.
|
|
ii)
|
Decreased
resistance to chafing tears and punctures.
|
|
iii)
|
Abnormal
strain on the valve base.
|
|
iv)
|
Shorter
life of tyre cover due to lower air retaining qualities of stretched tubes.
|
|
v)
|
Excessive
stretch and growth, which listen deterioration of the tube rubber.
|
|
d)
|
Never
use a tube in a tyre cover of a size smaller than that for which the tube was
designed. The tube will crease and fall prematurely.
|
|
e)
|
Always
use a new valve core.
|
|
f)
|
Make
certain that the surface of the tube is clean and dusted with French chalk
before mounting.
|
|
g)
|
Ensure
that the end of valve is clean before applying the air hose, this prevents
dust and dirt being blown in to the tube.
|
|
h)
|
Always
check pressures with an accurate pressure gauge and ensure that correct
pressures are maintained.
|
|
j)
|
Always
replace the valve cap after inflating the tyre.
|
|
k)
|
When
un mounted tubes are inflated for inspection they should not be inflated to
the point of “Ballooning”.
|
|
21. Storage
of Tyre covers & Tubes & General precautions.
Factors
that contribute to the deterioration of stored covers and tubes are:-
a)
|
Light
(particularly sunlight, which is rich in ultra-violet rays).
|
b)
|
O
zone (from electrical generators etc.)
|
c)
|
Heat.
|
d)
|
Air
currents.
|
e)
|
Oil.
|
f)
|
Water.
|
h)
|
Dust
and Dirt.
|
Any
storage place should therefore be protected from these deteriorating agencies,
which adversely affect the physical properties of the rubber, and hence the
useful life of the articles.
i)
|
The storage place should be kept as
dark as possible, windows and skylight should be covered with a dark point
and doors and openings kept closed as far as possible. Electric lights should
not be left burning beyond the time necessary for work to be carried out in
the stores.
|
ii)
|
If the stores cannot be darkened for
some reasons the rack should be covered with tarpaulin or other closely knits
fabric to exclude light
|
iii)
|
Covers and tubes should not be
stored near electric motors, switch gear etc as these generate Ozone which is
very destructive to rubber.
|
iv)
|
The store room should be kept at a
reasonably low and uniform temperature (70 to 80 F). In hot territories where
this cannot be achieved the store building should be insulated from the
direct run as far as possible. Such materials such as corrugated Iron should
be avoided. In cool territories covers and tubes should be kept away from
radiators and stream pipes.
|
v)
|
Draught changes in the humidity of
the air in the store should be avoided as far as possible as moisture will
condense and collected inside the castings. This is not so serious with new
covers, which usually have an adequate layer of rubber protecting the inner
ply. Used covers often have cords exposed due to cuts etc. which allow
ingress of water. Rotting of the casing can cover under these conditions.
|
vi)
|
It is not good practice to Place or
stag or the tyre in piles, this tends to discomfort the bead wires and
casing. If the black method is tied cover should be carefully aligned and the
height restricted to the six feet.
|
vii)
|
If the black method used the mixing
of sizes should be avoided. Larger and heavier cover should never be stacked
or smaller sizes, if mixed sizes must be stacked the sizes should be graded
so that the smallest and lightest is at the top of the stacks.
|
viii)
|
Before storing out covers they
should be inspected and any necessary repairs made. (Oil and grease should be cleaned off, if
perfect).
|
ix)
|
When making issues from a tyre store
the principle of “First in, First out” should always be adhered to.
|
For Tubes
|
|
i)
|
New tubes are usually received
packed in cartoons or bays and they should not be taken out of these
containers until required for use.
|
i)
|
Large stocks of tubes should not be
carried as physical properties tend to deterioration on prolonged storage
especially in hot climate.
|
iii)
|
In case where tubes are received
fitted in the covers, with or without flaps, the pressure should be reduced
to minimum to retain the tube in the cover. The assembly can be stored in the
usual way of covers, but it is most important to keep light away from the
portion of the tube exposed between the cover beads.
|
iv)
|
Used tubes should be deflected by
removing the valve core, examined and any necessary repairs made. The valve
core then be re-inserted and a small amount of air out into the tube, which
is then folded carefully and stored in a cartoon or bag of suitable size if
available. Used tyres can be stored slightly inflated in side cover is used
care paragraph above.
|
v)
|
Whichever meth of storage is used
care should be taken to exclude light from the tube.
|
22. The position of tyre to obtain maximum
service
It
is important to remember that irregular and for rapid wear can be caused for
many reasons. Here we confine ourselves to a consideration of the means of
obtaining even wear and maximum service from tyres, by utilizing of tyre
positioning and rotation.
23. The proper matching of Dual Tyres
The proper matching of dual tyres is
extremely important if maximum tyre service is to be obtained. The secret of
dual tyre matching is to obtain as far as possible, an equal distribution of
the load between the two tyres, forming a twin assembly. If for any reason
there is an unequal distribution of the load between the twin tyres of a dual
assembly, then affective rolling circumferences of the tyres will be different,
and they will “fight” due to the fact the wheels are rigidly bolted together.
As a result the tyre carrying the smaller load will “scuff” will be liable to
fail prematurely.
Factors
that will prevent an equitable distribution of the load between the two tyres
of a dual tyre of a dual tyre assembly are:-
i)
|
The
relative diameters of the twin tyres.
|
ii)
|
The
amount of air pressure in each tyre.
|
iii)
|
The
crown of center of the road.
|
iv)
|
Loose
wheel bearings.
|
v)
|
Axle
sag.
|
The
manner of matching tyres may vary considerably for different conditions of
operations, but if there is no previous experience to uses a guide for a
particular vehicle in a particular type of service, than the best thins to do
is to apply two tyres approximately of the same diameter of the same diameter
to each dual assembled. In practice however the right prove difficult, and the
some tolerance is allowed. The most desirable matching obtained by not
exceeding 19.05 mm approximate circumference, or 6.4mm approximate in diameter
for tyre sizes up to including 8.25 and 38.1 approximate difference in
circumference or 12.7 mm approximate in diameter, size 9.00 & upwards.
Although
not strictly correct in every case it may be taken as a general rule when
fitting tyres of different diameters with in the tolerance mentioned above, that
tyre having the smaller diameter should be fitted to the inside position.
24. The importance of fitting a tyre to
correct size of rim and the importance of fitting twin tyres to rims having the
correct off set
It
is not important when tyres are fitted in twin formation that times having the
correct off set are utilized. The followings notes will underline the
importance of using a correct tyre/rim/off set combination.
i)
|
Each and every size
of tyre is designed and manufactured to fit ideally on to one
size of rim only.
If the rim is wider or narrower than the ideal, than un-natural stresses will
be set up in the body of the tyre, and the tyre will not be permitted to
deflect according to the tyre designed is intentions. The result will be a
reduction in tyre life and the possibility of complete premature failures.
|
ii)
|
If there is
insufficient space between twin tyres there is a risk that the side walls of
the tyres will rub together generating excessive heat which cannot be
dissipated. In addition the tyres will effectively be prevented from
defecting properly and this will set up un-natural
stress in the tyre ear case. The result will be premature failure. It
must also be noticed that the tyre rubbing can occur even when tyres are
mounted on the correct rims with the correct off set due to conditions of
over loading and / or under inflation.
|
iii)
|
If the dual
inflation is too great there will be an unequal load distribution between two
tyres on cambered roads. There will also be excessive dragging and scuffing
of the outside tyre each time a corner is negotiated. The result will be
rapid tread wear on the outer tyre and / or premature failure of the inner
tyres.
|
25. Repaired tyres should be mounted in the
outside dual position. When the repair is in the shoulder or side wall area the
tyre should be so mounted on the rim that the required section is next to the
locking ring or loose flange sides. The repair job will thus be in the center
of the dual tyre assembly which is the easiest position. Should a tyre have
more than one repair, give the major repair job first consideration when
mounting.
26. ff Set
Off
set is the measurement from the center line of the tyre to the outer half face
of the wheel disc. Dimensionally, when tyres are being used in twin formation,
the off set is half the distance between the center lines of twin tyres.
__________
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