SX2 understeer - best tyres for astro?

[Cardnim]

Hi guys,

Im having loads of understeer when racing on astro. I normally race on clay/(mud!) and its fine there.

Ive tried laods of different set up sheets from here and Petit but cant seem to eliminate it (or even make it better!) and no one races the same car as me over here, so cant ask someone else.

Im thinking its tyres - as Ive only ever run mini-spikes or dBoots Terrabyte.
The terrabytes seem to make it worse!

What tyres should I be going for?
Ive seen a couple of guys racing staggered ribs on a 4wd wheel with no inserts. Would this work?

Sorry for the dumb question, but Im a bit stumped.

...oh, and Im pants at driving, so that probably doesnt help!