it is supposed to make turn in quicker due to the steeper profile of the 70 series (easier to get it on edge).
example....... (___) is 60 series (_) is 70 series. the 60 series has a flatter profile as compared to the 70 so it is "harder" to get over on its side. Harder being a relative term. There should be no modification necessary to the front fender or anything.
I myself have never tried a 70 series as the 60 seems plenty quick to me.
Ask one of the racers like RockyR6, TXR6 or R6#319. Pretty sure they all run 70 series as I'm sure alot of other member do to.
i have always used 70 profile tyres. penfold was almost right but its the side walls which are longer on a 70 profile, the tyre area which sits on the ground when the bike is up is the same on both tyres, but when the bike is crancked over the larger wall on the 70 profile mean a larger tyre footprint. o = 60 profile. 0 = 70 profile
i ordered my 70 series and they should be here tomorow i beleive. but ive heard you dont have to lower the forks but if you want the same steering geometry you have to lower them about 7mm. im sure someone will confirm this though :cheers