The belt skips more with the front diff fitted because you are breaking on the front wheels as well and thereofr have a ton more breaks.:)

I run Daryls's pulleys in my X5, you can get away with having the belt a little looser but still with no skip so the car is even freer running:D

The funny thing is it is when I'm accelerating. I don't have to break much as the track I race on is small and made to flow this layout. I sent Daryl and email to see about getting some of his pulleys. It would be nice if they were on his website.:(