I believe it's 24 and 25 tooth pulley. A 24 tooth on the side gives a little over drive (the rear turns less than the front). A 25 tooth will give more a 1/1 ratio meaning the front and rear wheels are driven at the same pace. But this all is dependant on you front and rear tire diameter. I believe this is correct. but don't qoute me. Look at the Rollout Chart from Mugen it will explain more.