Chevrolet DB90 Series, Руководство по обслуживанию

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S ec. 10-2
WHEELS
04_____________
AND TIRES
WHAT HAPPENS WHEN
TIRES GET HOT
As a | tir e b ecom es heated, the air in the tir e
expands ^nd the a ir p r e ssu r e is r a ised . T his is
norm al u n le ss the p r e ssu r e build-up is e x c e s s iv e .
B u ild -u p s|of over 20 lb s. a re e x c e s s iv e , indicating
underinfla^ion, overload, too much speed, too sm all
a tir e o r, m ore often, a com bination of th ese fa c ­
to r s . T herefore, p r e ssu r e build-ups of ov er 20 lb s.
should be studied to determ ine cause and proper
co rrective action. Norm al p r e ssu r e build-ups (not
over 20 lb s.) reduce flexin g. Thus the amount of
heat generated allow s the tir e to reach a heat b a l­
ance (the tem perature at which the rate of heating
equals the rate of cooling) at a low er tem perature
than if the inflation p r e ssu r e w ere m aintained uni­
form ly by frequently bleeding out a ir . T ir e s should
never be bled. When the p r e ssu r e builds up e x ­
c e s s iv e ly - reduce the sp eed or the load instead.
A tiro operated for a considerable distance at
sustained highway sp e ed s, in a se v e r e ly underin­
flated or flat condition, b ecom es extrem ely hot due
to interna] friction , and th is heat tra n sm its to the
tir e 's outer su rfa ce-. If and when the outer su rface
tem perature reach es the com bustion point, the tire
b u rsts into flam e. This usually occu rs after the
veh icle has stopped. Such an o ccu rren ce usually
in volves a dual a ssem b ly where one of the tir e s is
flat and tl^e other is , th erefore, extrem ely o v e r ­
loaded (possibly a lso underinflated ev en fo r norm al
load). In such c a s e s , either the tir e which is s e ­
v e r ely underinflated or com pletely flat, or the tir e
which is extrem ely overloaded, could get so hot a s
to rea ch the point of spontaneous com bustion.
CAUSE ANlD PREVENTION OF TIRE FIRES
A majf>r cause of tir e f ir e s is heat caused by
a dragging brake, p articu larly if th ere is e x c e s s iv e
g r e a se an d /or o il around the brake drum The heat
produced by the dragging brake ign ites the g r ea se
or o il which in turn can eventually ignite the tir e ,
even though the tir e is not overloaded or under­
inflated.
R eg a rd less of the cau se of a tir e f ir e , the
tir e 's interlnal tem perature is so high that even if
the flam es a re extinguished, repeated spontaneous
ignition o ccu rs until the internal tem perature de­
c r e a s e s su fficien tly . A fir e extinguisher usually
w ill not h ate su fficien t capacity to control the fir e
until the burning tir e can be rem oved. O perators
should carry sp e c ia l a sb e sto s blankets which, in
c a se of tirfe fir e , a r e useful in preventing the fir e
from spreading to v eh icle and cargo. If p o ssib le ,
a stead y stjream of w ater should be placed on the
tir e until it is cool enough for rem oval.
The b e st protection against tir e f ir e s is to
avoid running on a flat tir e , prevent underinflation
through regular checking of inflation p r e s s u r e s , and
avoid accum ulation of g r e a se or o il around brake
drum a r e a s. O perators carrying cargo which is
exp losive or readily com bustible should check tir e s
at 5 0 -m ile in tervals and should a lso u se a p r essu re
warning device.
INSTRUCTIONS FOR MAINTENANCE
OF TIRES ON OFF-THE-HIGHWAY
UNITS IN HIGHWAY TRANSIT
Many O ff-The-H ighway T ir e s a r e designed and
built to g iv e maximum s e r v ic e for mining and con­
struction operations. B eca u se of the extra heavy
construction built into th ese tir e s , sp e c ia l p reca u ­
tions m ust be ob served when equipment i s being
m oved ov er the highway for d elivery o r when tr a n s­
ferrin g to a new job s ite . If th e se p recautions are
not observed, the tir e s may build up e x c e s s iv e heat
and cau se prem ature fa ilu re.
The follow ing recom m endations a re made in
the in te r e st of p rotectin g your investm ent against
lo s s and delay. T h ese recom m endations apply to
a ll t ir e s on v e h ic le s in tran sit, whether driven or
towed.
LOAD AND PRESSURE
1. V eh icles m ust be empty during tra n sit.
2. Inflation p r e ssu r e is determ ined by cold
p r e ssu r e ch eck s b efore sta rtin g . P r e s s u r e i s not
to be reduced by "bleeding” t ir e s during tra n sit.
3. Inflation p r e s s u r e s are to be determ inedby
u se of the follow ing ch arts. If load cannot be a c ­
curately estim ated , u se the m axim um inflation
p r e s s u r e shown fo r the ply rating in question.
4. T ir e s with "dry" b allast must not be used
fo r veh icle transport p u rp oses.
SPEED
R egular Skid Depth T ir e s
1. Maximum highway sp eed 30 mph.
2. Stop for 30-m inute cooling period after
each 50 m ile s of driving or b efore 2 hours' s u s ­
tained operation, w hichever co m es fir s t.
3. One hour minimum m id-day lunch stop
should be ob served during fu ll day op eration s.
E xtra Skid Depth and S p ecial Compound T ir e s
V eh icles equipped with extra sk id depth or
sp e c ia l compound tir e s are not to be driven in
tra n sit ov er the highway u n less the proposed trip
is review ed and approved by qualified p erson n el.
Super Deep T read T ir e s
Under no circu m sta n ces should the Super Deep
T read tir e s be moved (roaded) ov er the highway.
V eh icles in tra n sit m ust be con trolled and a c ­
com panied by resp o n sib le p erson n el in a p ilot car
to en force recom m endations and m aintain a check
on equipment. T his is good in surance fo r a v a l­
uable investm ent.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT