(especially with wide tires) can most certainly spray rocks back at cars behind them... something else that the mud flaps help *minimize* (I won't say eliminate).
If you sped past me and put a rock in my windshield and I saw that you didn't have mudflaps I'd want to chase after you and beat the piss out of you.
Z-Jay Vice President - Edmonton Z Car Club 93 300ZX TT - Stage VI