Did you guys running underdrive pulleys buy this? Im an a4 and looking at slp and im wondering if i need this.

 

unless you have an audio system i would say you dont need it. but it wont hurt at all if you worried about charging in traffic.

 

I needed one once my OEM alternator went bad and I needed to find a replacement. I couldnt find a aftermarket alternator that performed like my OEM and the overdrive pulley helped with charging at an idle. But my alternator just took a crap on me and I am trying to figure out if my overdrive may have killed it.