What is a Floating rotor?
A Floating rotor is made up from two parts. There is the center that mounts to your hub and the stainless steel braking surface that contacts the brake pads when stopping. They are connected by rivets. Once you bolt the rotor mounting surface to your hub the braking surface is able to float on the rivets allowing it to move slightly when expanding and contraction during heat and cooling cycles.
Why does it Float?
When the rotor is subjected to serious heat from braking it expands. By allowing it to float separately from the mounting face it is free to expand and shrink again at will without being constrained. When expansion takes place is does so in all directions at once and it will not be constrained. If you prevent this from happening in one direction it has no choice but to warp.
Do I need a Floating Rotor?
For the average rider using your SM bike to ride to work and occasional high speed cornering down the canyons the standard rotor works great. Unless you are using your front brake excessively or racing you do not need the floating rotor. The 320 mm rotors work great and are designed to work under load. The floating rotor is for extreme braking and riders who have a tendency to get the front rotor extremely hot and cause them to warp.
Can I run my stock size front rotor?
Yes you can. Using the stock size rotor make it easier to switch back an forth from your dirt wheels to your supermoto wheels. One thing to keep in mind. Using an oversized rotor will reduce the pressure you need to put on your brake lever to stop your bike. It will also help keep your front rotor from getting too hot. With the smaller rotor it will take more force on your lever to get the bike to stop. And with the smaller surface area the stock rotor will get hotter than the oversized causing to warp.