Well...I'm no suspenders expert, but I'm sure someone with more knowledge and experience will say something along the lines of 'every rider is individual...so is every bike, and every riding style...etc...', so there is no golden rule to follow regarding the 'right' spring.
The 7.4 kg/mm spring is a relatively stiff one, and I think it is the standard spring for a Bip which shows how stiff it is. I have a spring rated around 6.5 or summut. The softer spring gives a nicer ride on the road, but I guess you get more squat when on the gas, equating to perhaps running wide out of the turn blah, blah, blah...
I think a softer spring may help you if you ride on the road...but for the track...perahps its about right?
Pay an expert to set the bike up for you...couple of hundred quid well spent.
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