S e c . 10
P age 64
WHEELS A N D TIRES
Figure 12— Tire Rotation
TIRE ROTATION
G enerally, it is the b est p ra ctice to "breakin"
new tir e s on front w h e e ls. "Breaking in" on an easy
p o sitio n g en erally in c r e a s e s the overall tir e life.
The m ovem ent of the tir e s from front to var
io u s rear w heel p o sitio n s depends upon the type of
unit being operated. It is generally n ec e ssa r y to
u se tir e s with good n on -sk id tread design on drive
w h eels.
T ir e s with le a s t tread design should be used
on tr a ile r w h eels, and particu larly on the rear of
tandem w h eels. This is due to the fact that cuts are
found m ore often on the tr a ile r and rear tandem
Figure 13— Tire Rotation
t ir e s and by using w ell worn tir e s on th ese w h eels,
lo s s on tir e s due to road hazards is m in im ized .
NOTE: When rotating any tir e , follow re c o m
m endations in " selectio n of tir e s" a s cov ered p r e
v io u sly .
TWO-AXLE TRUCK
T ir e s should be m oved from front w h eels to
rea r w h eels (fig. 12) after 1 /3 of the tread design
is worn off. If th ere is uneven front w heel tir e
w ear, rotate tir e s im m ed iately and check v eh icle
for m echanical ir r e g u la r itie s . When tir e s are
m oved to the r e a r , follow recom m endations in
m atching them with other t ir e s .
TRUCK WITH TANDEM AXLE DRIVE
Follow the sam e p r a c tice a s d escrib ed for
sin g le -d r iv e axle except tir e s must be rem oved
from the fronts at l e s s s e r v ic e in order to provide
8 tir e s for the rea r w h eels in stead of 4 for the
sin g le -a x le d rive. Since th ere a re 5 tir e s on each
sid e of the v eh icle (fig. 12) the front tir e s should
be m oved to the rear when 1 /5 of the tread design
is worn off. Then match t ir e s on each w heel as
already d escrib ed but with an additional precaution
- the sum of the c ircu m feren ces of the four tir e s
for the front of the tandem drive a x le s should equal
the sum of the cir c u m fe re n c e s of the four tir e s on
the r e a r of the tandem a x le s. T his precaution is
n e c e ssa r y to p reven t e x c e s s iv e w ear from slip p a g e.
If th ere is a third d ifferential betw een the two drive
a x le s , th is precaution is u n n ecessa ry .
TRACTOR AND SEMI-TRAILER
A fter 1 /5 of the tread design is worn off, tir e s
should be m oved from the front to the in sid e or
outside driving w h eels (shown in figu re 13), the
p osition being determ ined by matching a s re c o m
m ended. L ater the tir e s should be m oved to the
tr a ile r w h eels. The p o ssib ility of injury from cuts,
b r u is e s , e tc ., is g rea ter in the tr a ile r w heel p o s i
tion. By follow ing th is rotation plan with t ir e s , end
ing th eir s e r v ic e on tr a ile r w h eels, at le a s t the
g r ea ter portion of the tir e s e r v ic e has been ob
tained even if they a re damaged.
TRACTOR WITH TANDEM AXLE DRIVE
WITH SEMI-TRAILER WITH TANDEM AXLE
Follow sa m e p roced u re a s above for tra cto r
and s e m i- t r a ile r with s in g le -a x le except tir e s m ust
be rem oved from the front w h eels at l e s s s e r v ic e
in ord er to provide for 16 tir e s in stead of 8. Since
th ere a re 9 tir e s on each sid e of the v e h ic le , the
front tir e s should be m oved to the rea r when 1 /9
of the tread design is worn off (fig. 13). Then match
tir e s on each w heel a s already d escrib ed but with
an additional precaution - the sum of the c ir c u m
fe r e n c e s of the 4 tir e s fo r the front of the tandem
