xr4i is smaller diametre.
The original 3 door front arb is the best imo, gives very twitchy steering, and the 3 door hubs are best.
A lot of owners had the arb changed under warranty by ford after complaints about instability, they basically increased the castor with the modded arb's whichlater were std sapph 2wd ones, same diametre 28mm.
tabetha