Whats the speed rating for a 205/50/16 on a sti type ra, reason being that when using the adjustable diff on the 2 notch before full lock, when driving the tyres are are skidding for some reason and don't know why.

help please.

?? Could you describe in a little more detail what is happening here please, as it's not really clear from what you've said.

Given your current description, it sounds like the front wheels are "pushing on" when you're turning, and presumably this behaviour is more pronounced the tighter the corner you turn. If so, that's normal behaviour with the DCCD wound up. The answer is not to drive round with the diff wound up... ;)

FWIW the standard 205/50 x 16 Bridgestones are usually V (up to 149mph) rated, although I doubt this has any bearing on your "problem".