You won't break the standard 1200 castor bars on the road or track. But I can understand rally cars upgrading them.

I still use the standard bars and had them threaded for adjustment, and they've taken all my kerb hopping, wheel lifting, (and occassional bush bashing) antics on the track... I even ran up a bank a bit at a hillclimb once and tore the castor bar mount half off the body, but the castor bar was undamaged. Moral of the story - don't add weight where you don't have to