Much, much more than a 1000th of a second - same goes for flapping clothing. Got to be aero!! However, in response to your main point, my winter bikes have mudguards and if anybody turns up without them on a club run they are sent to the back where they won't splash everybody else.Why do you bike nutters ride bikes without mudguards? Maybe it slows you down by 1000 of a second at best. ! PS, Old Brit, still looking good for an old geezer.