I am fitting cosworth 4x4 front and rear brakes to my S1 and I see that some people fit inline brake bias valves. Do I need to fit one or will it be ok without?

 

Not too sure mate, the aim of the game is to stop the rears from locking up. In all honesty you won't gain much at all by fitting rear disks (but they look pretty).

Your best bet is to remove the abs completely, use standard front callipers with brackets for cossy disks, and use a proportioning valve (either wilwood or ford inline).

Rob,