K1 Aero setup help

[Moss Models]

Can any superstars help me with this.

Compared to my normal K1 my aero has bugger all rear end grip on low grip surfaces.

I know the geared diffs may be the problem. I am running 12k front and 7k rear. Core 400wt front and 300wt rear. Other than that the car is stock. I generally find with all schumacher cars the stock settings about right. I have run the car three times now and yesterday the car bordered on undrivable. Surface is polished gym floor (benfield).

Shall I go back to ball diff in the rear?