thank you MasterQ32.
i test that way and this is the problem:
if i create decals for tire ,what can i do to restrict it's count?
3 car with 4 wheel means 12 object to make tire marks and very easy ,in one minute , there is thousands of them in level.and if each one has an action we
have thousands of functions that reduce frame.

why particle system don't have decal flag?