Originally Posted by asw7576

Rear A block : More on-throttle grip, Less grip under braking, More body roll, Use under low traction conditions to get more steering, Increases overall traction, reduces rear tire wear,

Rear B block : neutral -- between A and C

Rear C block : Less on-throttle steering, Car is more responsive, Use in high grip conditions to avoid traction rolling, Use on tracks with quick direction changes (chicanes), more side bite only, less body roll, preferably for track with lots of S turns.