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Sec. 10
P age 64
WHEELS A N D TIRES
Figure 12— Tire Rotation
TIRE ROTATION
G enerally, it is the best practice to "breakin"
new tir e s on front w h eels. "Breaking in" on an easy
p osition generally in c r e a se s the overall tire life.
The m ovem ent of the tir e s from front to var
ious rear w heel p osition s depends upon the type of
unit being operated. It is generally n ecessa ry to
u se tir e s with good non-skid tread design on drive
w h eels.
T ir e s with le a st tread design should be used
on tr a ile r w h eels, and particularly on the rear of
tandem w h eels. This is due to the fact that cuts are
found m ore often on the tra iler and rear tandem
Figure 13— Tire Rotation
tir 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 inim ized.
NOTE: When rotating any tir e , follow reco m
mendations in " selection of tir es" as covered p r e
viou sly.
TWO-AXLE TRUCK
T ir e s should be m oved from front w h eels to
rear w heels (fig. 12) after 1 /3 of the tread design
is worn off. If there is uneven front w heel tire
w ear, rotate tir e s im m ediately and check veh icle
for
m echanical
ir r e g u la r itie s.
moved to the rea r, follow recom m endations in
m atching them with other tir e s .
TRUCK WITH TANDEM AXLE DRIVE
Follow the sam e p ractice as described for
sin g le -d r iv e axle except tir e s must be rem oved
from the fronts at le s s se r v ic e in order to provide
8 tir e s for the rear w heels instead of 4 for the
sin g le -a x le d rive. Since there are 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 tir e s on each w heel as
already d escribed but with an additional precaution
- the sum of the circu m feren ces of the four tir e s
for the front of the tandem drive a x les should equal
the sum of the circu m feren ces of the four tir e s on
the rea r of the tandem a x le s. This precaution is
n e c essa r y to prevent e x c e ssiv e w ear from slippage.
If there is a third differential between the two drive
a x le s, this precaution is unn ecessary.
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 heels (shown in figure 13), the
position being determ ined by matching as reco m
mended. Later 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 ise s, e tc ., is grea ter in the tra iler w heel p o s i
tion. By follow ing this rotation plan with t ir e s , end
ing their se r v ic e on tr a ile r w h eels, at le a st the
g reater portion of the tir e se r v ic e has been ob
tained even if they are damaged.
TRACTOR WITH TANDEM AXLE DRIVE
WITH SEMI-TRAILER WITH TANDEM AXLE
Follow sam e procedure as above for tractor
and se m i-tr a ile r with sin g le -a x le except tir e s m ust
be rem oved from the front w h eels at le s s s e r v ic e
in order to provide for 16 tir e s instead of 8. Since
th ere are 9 tir e s on each sid e of the veh icle, the
front tir e s should be m oved to the rear when 1 /9
of the tread design is worn off (fig. 13). Then match
tir e s on each w heel as already described but with
an additional precaution - the sum of the cir c u m
fe r e n c e s of the 4 tir e s for the front of the tandem
When tir e s are
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