MAD Wurks Carbon Split Narrow Rear Topdeck 1.5mm Schumacher Mi9 (1)

MAD Wurks Carbon Split Narrow Rear Topdeck 1.5mm Schumacher Mi9 (1)

To add additional flex to suit your needs, you can cut one or multiple bridges out.
You also can cut from the front slot into the adjoining screw hole. This allows much more torsional twist.  

Adding flex allows the rear of the car to roll more and better wrap the corner.  
Adding too much flex can sacrifice rear end stability.

Starting recommendation on top decks is to run them as they come for most surfaces and conditions.

For the 1.5 top decks, you can use the 1.6mm dowel bushing that comes in the alloy kit (U8775).  
We've also found that using the standard 2mm dowel bushing (u7783) that comes in the asphalt kit with a 3mm id x 1mm thick oring is a good option. It provides a consistent feel taking up the slack but still allowing movement.  Note this will also work for the 1.6mm S2 factory decks as well.