How the prosaic Fiesta gets turned into the winning ST.

Interesting. The standard Fiesta has a bigger front sway bar.....hmmmm. Fodder for AX....

My thought exactly..would like to know why? Fittament issue is my guess, but hard to comprehend if that is the case.

Don't you play with the Rear bar on FWD and they did that by making the rear beam stiffer.. Or not ?

Smaller bar = more front grip, less likely to understeer. Moving to a large front bar will increase understeer.

They increased the spring rates and lowered the car, that raises roll stiffness independent of the anti-sway bar.

They probably reduced the bar because the standard bar was too much with the stiff springs.

To make the car oversteer they increased the rear roll stiffness which improves side to side weight transfer at the front.

Its a delicate balance to get handling without sacrificing too much ride quality.

With race rubber and coilovers, a bigger bar might make sense at some point but the ride at that point might not be very street friendly.

back in the olden days of SCCA Solo we were not allowed to substitute, add, or remove the rear anti-roll (sway) bar in Stock. So the trick was to fit a smaller front anti-roll bar from the base model if you had a car that came in a base and an up-level suspension option.