I just spent a week in the Oregon dunes with my yz125. it did just fine on almost every large dune. Just keep in the throttle and make sure to check your float before going. i had a problem with my float and was running out of gas 3/4 of the way up, replaced the float and was fine after a short down time. other than that little glitch my 125 had enough power to take me anywhere my friends with larger bikes were going as long as i had a hand full of throttle.