I usually take them off the night before an event. I like to drive out there that way to get the engine management used to the difference in backpressure. After the event then I am usually to tired/lazy to put them back on so they stay that way for 1 -several days. It does sound fricken awsome, but in the city the reverberation off of buildings is pretty intense. I have seen women and small children run (not really but you get the idea)!! I also sorta like to go to the dealership with them off just to scare all the damn yuppies that like to frown on this 'strange bimmer'...