hello 907 riders im looking to improve the brakes on the old chook ithink ductile steel would suffice if anyone knows where i can get any or any other ideas would be helpful i just finished an 8 year love affair with an 851 which had 320mm floating rotors those brakes were so powerful so im hoping just changing to a different rotor will do the trick ialso run collector plates so ihave to keep it somewhat stock i have just rebuilt the m1r forks so would like to keep them ive had the bike for 18 years now so i understand options are limited but any tips would be great thanks terry aka bonza

According to Wikipedia they both weigh near as dammit the same , so the 851 doesn't have a weight advantage . I would be looking to experiment with different pad compounds before I tried different disc's ( way cheaper )

As Hamish says trying different brake pads is the cheapest way to go.
Sintered pads could be worth trying if you don't ride the bike very much since they will wear the discs quicker if these are cast iron.
Otherwise (as listed in the FAQs) there're some Yamahas that also use 300mm discs with the same dimensions.

Of course if you still have the original brake hoses get rid off them and replace them with steel braided lines.

The issue is not the size or tipe of rotors but the Mastercylinder... the original (20 odd yeard old by the way!) is simply crap.

My feeling is that the design of the particular MC was intended to make it less harsh when braking (it has quite a lot of travel), this way makes it less ready and does not give that confidence you have on more modern Setups.

Funny enough the same MC (from the looks of it) on my SS and it has exactly the same feeling despite having 320mm rotors... Spongy.

I went and replaced all MCs with the Gold Line "Serie Oro"" from the 916 and I will never go back.

I am running Discacciati Cast Irons with Ferodo CP911 organic pads, only reason for replacing them was because one was warped, but braking has never been an issue since I replaced the MCs.