WHEELS, RIMS AND TIRES WHEEL AND TIRE BALANCING Front  wheel  and  tire  assemblies  must  be  balanced  to prevent  wheel  vibrating  and  bounce.    While  the  correct front wheel alignment is necessary for easy steering and maximum  tire  life,  the  cause  of  unstable  steering  can frequently be traced to improper balance of front wheels. When this condition exists, the wheel and  tire  assembly should be properly balanced. A vulcanized or retreaded tire, or a tire that has a boot in it,  may  cause  an  unbalanced  condition  that  cannot  be corrected by balancing.  In such cases the tire should be replaced before attempting to balance the assembly. Static Balancing A   wheel   out   of   balance   statically   has   a   tendency   to bounce up and down, resulting in rapid tire wear in round or oblong spots. Static balancing is performed while wheel is stationary by attaching   weights   to   rim   flange   to   offset   an   opposite heavy point. Static   balancing   may   be   sufficient   in   some   instances where vehicle is operated only at slow speeds, however, dynamic  balancing  (in  motion)  balances  the  wheel  and tire  assembly  statically  as  well  as  dynamically,  thereby eliminating vibrations and wheel bounce at both low and high speeds. A   wheel   may   be   perfectly   balanced   statically   (not   in motion)  but  may  still  vibrate  and  bounce  at  high  speed rotation because of its being out of balance dynamically. Dynamic Balancing Dynamic balancing is complete wheel balancing of which static balancing is only a part. Dynamic  balancing  (in  motion)  takes  into  consideration the distribution of weight to be added to the wheel.  This Is     accomplished     by     rapidly     rotating     (normal     truck operating  speed)  the  wheel  and  tire  assembly  either  on the  vehicle  or   with   the   wheel   assembly   removed   and placed     on     a     dynamic     balancing     machine.          This determines heavy point on wheel. When  the  amount  of  weight  required  to  offset  a  heavy part   in   a   wheel   assembly   is   known,   it   is   sometimes necessary to attach one-half of the weight to the outside rim flange and the remaining half to the inside rim flange. With    the    weight    properly    distributed    on    the    wheel assembly, the wheel should be in balance both statically and  dynamically  and  should  rotate  free  of  vibration  and bounce at normal truck operating speeds. TIRE CARE Proper   tire   inflation,   tire   loads,   and   road   speeds   are important   determining   factors   governing   tire   mileage, and also affect steering ease and maneuverability.  How much these three factors affect tire wear is illustrated in the paragraphs which follow. INFLATION Tire    pressures    should    be    checked    at    regular    and frequent    intervals    and    the    pressures    maintained    to specifications.  Use an accurate tire pressure gauge and check when tires are cool. Over  inflated  or  under  inflated  tires  will  reduce  the  ser- vice life of the tire. "Bleeding" of air from hot tires should never be practiced. The    pressure    will    be    reduced    but    an    increase    in temperature will result as soon as driving continues. LOADS Loading  tires  beyond  their  rated  capacity  is  expensive because    tire    mileages    are    rapidly    decreased    with overloads. TIRE MATCHING Dual Tires Use care in matching dual tires.  Tires which differ more than  6.35  mm  (1/4")  in  diameter  or  19.05  mm  (3/4")  In circumference should not be mounted on the same dual wheel.  Should it become necessary to mount two tires of unequal size on the same dual wheel, place the larger or less worn tire on the outside. Tandem Drive Axles When  mounting  tires  on  tandem  drive  axles  follow  the same  instructions  as  specified  for  dual  tires.    However, never install the four largest tires on one driving axle and the   four   smallest   on   the   other.      This   method   of   tire mounting  will  cause  high  lubricant  temperatures  which may lead to premature axle failures. CTS-4148A Page 22