contra spring and gear up kit questions?

Hi all i jus basically wanted to know when a stronger contra spring and gear up kit should be fitted and what the benefits would b.i got a piaggio zip 70 with leo vince zx exhaust yellow doppler clutch springs malossi 5.5g rollers jetted to 74.also i would like to find out how to tell when u have got the correct weight rollers in.all feedback appreciated.
cheers
Neo

 

have a look at the roller guide has some good info on it
http://www.scootershack.co.uk/rollerguide.html