A boy was being bullied(I guess) by another boy then a man steps out of his car and kills the bully with the bike's tire... please help me

Sounds like you might be looking for Pet Sematary Two...
....The next day, Jeff encounters the school bully, Clyde Parker in a ditch. Clyde is about to cut off Jeff's nose with the spokes of his own bike when Gus arrives. Gus orders Jeff to go home, then kills Clyde with his motorcycle. Drew witnesses the killing.....
Pet Sematary II (1992) - IMDb (http://www.imdb.com/title/tt0105128/)

Sounds like you might be looking for Pet Sematary Two...
....The next day, Jeff encounters the school bully, Clyde Parker in a ditch. Clyde is about to cut off Jeff's nose with the spokes of his own bike when Gus arrives. Gus orders Jeff to go home, then kills Clyde with his motorcycle. Drew witnesses the killing.....
Pet Sematary II (1992) - IMDb (http://www.imdb.com/title/tt0105128/)

Oh my god THANK YOU SO MUCH, it is it! Cheers:)

Great! :)