I've never really seen any negative effects as its been compulsory since I started racing so don't know any different. Just when I hear fanciers talking of the good old days,when doos were apparrently healthier and losses were less.Makes me wonder.Think I'm barking up the wrong tree with PMV jagging. Theres always been losses and you'd have to say theres more than one contributing factor to some of the eratic racing in recent years.