The PowerDome, an ingenious pyramid...
The brand new Sram RED cassette definitely scored a bull's eye when it was unveiled the last summer, during the Tour de France. Indeed, while most manufacturers didn't change a single element of the cassettes since ages, Sram had the idea and the opportunity to change this. The system is quite simplistic in the absolute. Actually, every revolutionnary components are designed through a simplistic idea.
Usually, every cassettes are composed of differents cogs attached to the rotor splines. Sram wondered if all these contact were really necessary and, what would happen if the contact was smaller. Why keeping the contact area of each cogs? And what would happen if only a few of them would transfer the torque? Finally, why not fixing all the cogs together and removing the central material?
That is why Sram developped the PowerDome technology: the height largest cogs of the cassette are machinned out from a single piece of chromoly steel, and the central material is machinned too.
Have a look at this:
So many advantages...Only three cogs are in contact with the freewheel body: the largest through the Sram Red stamped red alloy insert, and the two smallest. This brings several advantages:
On our scale, the 11-26 cassette weights exactly 161g without the lockring, which is 6g.
How does it work?
In practice, this cassette is to be mounted only on a 9s Shimano body. Indeed, the splines of a Shimano 10s rotor are deeper and can't receive this component.
We fear the low contact surface with the freewheel bodies, it is reduced to a single cog for the eight smaller gears. We hope the alloy rotors will hold well under the torque created by the pedals strokes...
We will keep you updated about it in a few weeks when the component will have some hundreds kilometers. To be continued.