Protector ply Bolt plies Tread reinforcing plies Casing outer ply Casing outer ply Normal tread wear on a radial tire Normal tread wear on a bias tire suspected damage, and areas with leaks should be marked  with chalk, a wax marker, paint stick, or other device before  the tire is deflated or removed. Often, it is impossible to  relocate these areas once the tire is deflated. Tires removed  for retread should be marked in damaged areas to enable  closer inspection of the extent of the damage before the new  tread is installed.  [Figure 13-137]  Asymmetrical tread wear may be caused by the wheels being  out of alignment. Follow the manufacturer’s instructions  while checking caster, camber, tow-in, and tow-out to correct  this situation. Occasionally, asymmetrical tire wear is a result  of landing gear geometry that cannot, or is not, required to be  corrected. It may also be caused by regular taxiing on a single  engine or high-speed cornering while taxiing. It is acceptable  to remove the tire from the wheel rim, turn it around, and  remount it to even up tread wear if the tire passes all other  criterion of inspection for serviceability.  Foreign objects imbedded in a tire’s tread are of concern and  should be removed when not imbedded beyond the tread.  Objects of questionable depth should only be removed after  the tire has been deflated. A blunt awl or appropriately sized  screwdriver can be used to pry the object from the tread. Care  must be exercised to not enlarge the damaged area with the  removal tool.  [Figure 13-138]  Once removed, assess the  remaining damage to determine if the tire is serviceable. A  round hole caused by a foreign object is acceptable only if it  is  3 ⁄ 8-inch or less in diameter. Embedded objects that penetrate  or expose the casing cord body of a bias ply tire or the tread  belt layer of a radial tire cause the tire to become unairworthy  and it must be removed from service. Removal of a tire before it is worn beyond limits to be  eligible for retreading is cost effective and good maintenance  practice. Considerable traction is lost when tire tread is  severely worn and must also be considered when inspecting  a tire for condition.  [Figure 13-136]  Consult airframe  manufacturer and tire manufacturer specifications for wear  and retread limitations. Cuts and tread undercutting can also render a tire unairworthy.  A cut that extends across a tread rib is cause for tire removal.  These can sometimes lead to a section of the rib to peel off  In addition to tread wear, an aircraft tire should be inspected  for damage. Cuts, bruises, bulges, imbedded foreign objects,  chipping, and other damage must be within limits to continue  the tire in service. Some acceptable methods of dealing  with this type of damage are described below. All damage,  Tread Damage Protector ply Bolt plies Tread reinforcing plies Casing outer ply Casing outer ply Figure 13-136.  Tread wear on a bias ply tire (left) and a radial tire (right) show wear beyond limits of serviceability but still eligible to  be retreaded. Figure 13-135.  Normal tire wear. 13-82