I ride the dunes exclusively and traded the stock rear for a 39 tooth. Like that better than the stock setup. Pulls all the way through 2nd and 3rd in drag races and still has plenty of top end speed. Works well when riding fast trails and large dunes. If I do engine mods/more HP, may go back to the stock gearing but ok for now. I ran a 6.221 but average about a 6.3 run on staged 300 foot sand drag with a top speed of 49.9 MPH. This set up will outrun the stock yfz450 with the minor mods like peashooter, airbox, jetting. I think the predator has alot more potential HP but waiting for a proven, tested, reliable engine kit/cdi box combination at a reasonable price!