Chevrolet DB90 Series, Service Manual

Page: 199 / 242

S ec. 10-193
WHEELS AND TIRES
Figure 11—Types o f Tire M easurem ent
In addition to matching individual tir e rolling
radii or rollin g circu m feren ce, we recom m end
matching, a s nearly a s p o ssib le , the total tir e
circu m feren ce of one driving axle to the total tir e
circu m feren ce of the other driving a x le. T his w ill
u su ally resu lt in sa tisfa c to ry tandem a x le lubricant
tem p eratu res that lengthen drive unit s e r v ic e with
higher tir e m ilea g e.
TRIDEM UNITS
When th ree driving a x le s are "hooked" together
in a T ridem S e r ie s , unmatched tir e s w ill compound
the p rob lem s d escrib ed in th ep reced in gp aragrap h s.
T h erefore, w e recom m end m atching, a s nearly
a s p o ssib le , the total tir e circu m feren ce of each
of the th ree driving a x le s.
HOW TO MATCH TIRES
TANDEM UNITS
The v eh icle should be on a le v e l flo o r, c a r r y ­
ing a co r r e ctly distributed rated capacity load. Be
su r e a ll tir e s a re the sam e s iz e (m easu re new tir e s
to be su r e they w ill be co rre ctly m atched).
1. Inflate a ll tir e s to the sam e p r e ssu r e .
2. C arefully m easu re the rollin g circu m fer­
ence of each tir e with a s te e l tape.
3. Mark the s iz e on each tir e with chalk and
arrange them in order of s iz e , la r g e st to s m a lle st.
4. Mount the two la r g e st tir e s on one sid e of
one axle and mount the two s m a lle s t on the opposite
sid e of the sam e a x le.
5. Mount the four other tir e s on the other axle
in the sa m e m anner.
6. T e st run the v eh icle to get accurate rear
a x le lubricant tem perature readings on the two
a x le lubricant tem perature gauges.
7. Vary tir e a ir p r e ssu r e , within the tir e
m anufacturer's recom m ended range, so the lu b ri­
cant tem perature of both a x le s i s within 3 0 °F ., of
each oth er and not in e x c e s s of 220° F. T his w ill
u sually re su lt in uniform tir e loading and good tir e
life .
F ollow the sam e procedure (Item s 1 thru 7)
fo r matching tir e s on a T ridem U nit. A rrange the
t ir e s in order of s iz e . The two la r g e st and two
s m a lle s t go on one a x le, the next two la r g e st and
s m a lle s t on the secon d a x le, and the rem aining
four on the third axle.
M easuring the circu m feren ces of the tir e s with
a ste e l tape a fter they a re on the rim s and inflated
but b efore they are applied to a v eh icle i s the m ost
accu rate method.
M easuring in th is m anner takes into account
any ir r e g u la r itie s in w ear. In checking tir e s a l­
ready on a v eh icle, eith er a square, s im ila r to but
la r g e r than a carp en ter's square, a strin g gauge, a
la rg e p a ir of c a lip e r s, o r a wooden stra ig h t-ed g e
long enough to lie a c r o s s the tread s of a ll four
t ir e s , may be used.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT