well most of them add a premium
IF you declare it. the reason behind it is simple . . . .make money.
in realilty they dont add alot of power to the bike. they dont cause accidents and they dont make that much noise compared to other bikes (stand next to a harley standard when it starts up) and they make you more noticable - reducing risk of an addicent (surely this should reduce your premium) and they are much cheaper to replace than the standard can.
so make some sense of it if you will
