You need at least the rear for the speedo to work correctly (I think only 1 rear will work but I cant remember) and you will need all 4 of them to make all the dash lights go off. There's a bunch of threads with good info on here and really everyone's figured out all the leg work so there's no real reason not to run them now that I can see
In talking with others found out you can splice in the wires from the front tone rings to the rear ones and hav the computer think there are four. Seems to work just fine ?? Others experience ??
Thinking of an F9 front with hubs, 5 on 5.5 37's max but more strength than the 44 and unit bearing ?? So no tone rings in the front.
I put 2 rings per side in the rear. Works perfectly no lights on my dash. Splicing wouldnt work for me... I tried all on 1 sensor and no bueno and then tried 2 per sensor and wouldnt work either. If some one gets it to work Id like to how they did it....