What is the best extinguishing agent when wheels catch on fire?
You can find some discussion in this thread but what you are looking for is 


  Fire Service manual. Volume 2. Fire Service Operations : aircraft
  
  incidents Home Office - London
  
  HMSO, 12/99. Crown copyright 1999
  
  ISBN 0-11-341192-8; 0113411928
  
  5.4.2 Brake and wheel fires The overheating of brake and wheel assemblies usually follows excessive braking. This can happen on
  landing when a hydraulic failure reduces the ability of the pilot to
  utilise control surfaces (flaps) and he feels the aircraft may over
  run the runway or more often, on an aborted take-off. Quite often
  tyres will burst or, as the aircraft comes to a standstill, ignite by
  transference of heat from the brakes. To avoid metal failure,
  firefighters attending overheated brake and wheel assemblies should
  usually refrain from applying water and allow natural cooling. If
  there is fire however, a fine water fog applied from fore and aft of
  the undercarriage assembly is generally used.