toe-in. The wheel alignment should be corrected to avoid  further  wear  and  mechanical  problems. BALANCE.—Correct  balance  of  the  tire,  tube, and wheel assembly is important. A heavy spot on an aircraft tire causes that spot to always hit the ground first upon landing. This results in excessive wear at the one spot and an early failure at that part of the tire. A  severe  case  of  imbalance  may  cause  excessive vibration  during  takeoff  and  landing.  This  makes handling of the aircraft difficult. Nylon Flat Spotting If the aircraft stands in one place under a heavy static load for several days, local stretching may cause an out-of-round condition with a resultant thumping during takeoff and landing. Dual Installations On   dual-wheel   installations,   tires   should   be matched  according  to  the  dimensions  indicated  in table  11-1.  Tires  vary  somewhat  in  size  between manufacturers and can vary a great deal after being used. When two tires are not matched, the larger one supports most or all of the load. Since one tire is not designed to carry this increase in load, result. AIRCRAFT TUBES a failure may Learning Objective:   Identify the procedures for  the  selection,  storage,  and  inspection  of aircraft  tire  tubes. The purpose of the inner tube is to hold the air in the tire. Tubes are identified by the type and size of the tire in which they are to be used. IDENTIFICATION Tubes are designated for the tires in which they are to be used. For example, a type I tube is designed for use in a type I tire. The size of the tube is the size of the tire in which it is designed to fit. Inner  tubes  required  to  operate  at  100  psi  or higher  inflation  pressures  are  usually  reinforced  with a  ply  of  nylon  cord  fabric  around  the  inside circumference.   The   reinforcement   extends   a minimum of one-half inch beyond that portion of the tube that contacts the rim. Table 11-1.—Tolerances for Diameters of Paired Tires in Dual Installations Tire outside Maximum diameter difference in outside diameters Less then 18 inches 1/8 inch 18 to 24 inches 1/4 inch 25 to 32 inches 5/16 inch 33 to 40 inches 3/8 inch 41 to 48 inches 7/16 inch 49 to 55 inches 1/2 inch 56 to 65 inches 9/16 inch More than 65 inches 5/8 inch Type III and type VII inner tubes have radial vent ridges  molded  on  the  surface,  as  shown  in  figure 11-29.  These  vent  ridges  relieve  air  trapped  between the casings and the inner tube during inflation. Inner  tube  valves  are  designed  to  fit  specific wheel  rims. However,   special   valve-bending configurations or extensions to provide access to the valve stem when you are servicing the tire may be required. TUBE STORAGE Tubes should be stored under the same conditions as  new  tires.  New  tubes  should  be  stored  in  their original   containers. Used tubes should be partially inflated  (to  avoid  creasing),  dusted  with  talc  (to prevent sticking), and stored in the same manner as tires.  Each  tube  should  be  plainly  marked  to  identify contents,  size,  type,  cure  date,  and  stock  number. Under no circumstances should inner tubes be hung over  nails  or  hooks. INSPECTION Inner  tubes  should  be  inspected  and  classified  as serviceable or nonserviceable. Usually, leaks due to punctures, breaks in the tire, and cuts can be detected by the eye. Small leaks may require a soapy water check.  Complete  submersion  in  water  is  the  best  way 11-28