I recently bought a front Formula 220mm disc rotor for downhill only use. Coupled with the Avid Code 5 hydraulic disc brake lever & caliper, stopping is very powerful, consistent and progressive. Braking action is not at all grabby as you might expect. At no time during a continuous 2000m descent I felt that the brakes were either too powerful or too weak.
In my experience, this rotor with its central alloy carrier also copes with extreme heat better than an all-steel rotor. After bedding in the disc & pads, I went down my standard steep street run and there was no sign of warpage due to heat buildup (the route drops 400 metres in 1.8km for an average 22.2% gradient). Steel rotors on the other hand tend to accumulate heat in the outer perimeter while the central splines remain relatively cool; the differential rates of expansion sometimes leads to severe warping. When it does occur, this happens immediately – rotors have all the lateral stiffness of a spinning pancake.
This disc is vastly superior to the Hayes V9 rotor I recently tested and reviewed. There is no comparison. The Formula 220mm disc rotor provides more predictable stopping than the Hayes 9″ rotor.
This rotor isn’t cheap, but you can get it with front IS mount for a shade over â‚¬60 from Chain Reaction Cycles. Adaptors generally cost about â‚¬10, so if you subtract the cost of that, the price of the rotor itself is more like â‚¬50, which isn’t so bad. A comparable 8″ rotor costs â‚¬30. Unfortunately, the central aluminium carrier only comes in only one colour: anodised red. Of course, this disc is completely overkill for most riders. But if you happen to live in a mountainous place and you regularly descend 20% grades, this won’t let you down.