How does the magnetic field get induced in car's tire? I was amazed to see how my car's tire started attracting the nuts and bolts, how in the world did it induce the magnetic field? Never heard of such phenomena!!!
 A: Car tyres, which these days are almost always radials, are sometimes reinforced with steel. It may be possible that these have become magnetized due to impact in the Earth's field, although I find that unlikely unless you constantly drive in one direction.
Otherwise, maybe someone has run a magnet over your tyres?
Adding quotes from another paper on the subject

Magnetic fields emanate from radial tires due to the presence of
  reinforcing belts which are made of magnetized steel wire. When these
  tires spin, they generate alternating magnetic fields of extremely low
  frequency (ELF), usually below 20 Hz. The fundamental frequency of
  these fields is determined by tire rotation rate and has a sinusoidal
  waveform with a high harmonic content. The static field of radial
  tires can exceed 500 microT at the tread, and the tire-generated
  alternating fields can exceed 2.0 microT at seat level in the
  passenger compartment of vehicles.

A: Tyres are made up of rubber. Rubber is an insulating material. During the movement of your car, the tyres get charged due to friction between the tyres and the ground. This causes your tyre to attract other charged materials or even nuetral materials.   
Charged rubber attracting nuts and bolts is difficult although it is not impossible. Nuts and bolts are conducting material, thus even if they are charged, charge leaks to the ground. In your case, your tyre should have had more charge which could attract neutral bolts and nuts due electrostatic induction. 
