As far as the wr vs crf goes...the crf230f is basiclly the same single cylinder engine design Honda has had for 30 plus years...mild, tractable power, excellent long term reliability. The Yamaha wr however...that may have a similar displacement, but thats it! The wr motor is essentially one cylinder off of a formula one engine!!! think of the honda motor as a 68 chevy 235 straight six, and the yamaha engine as a 2001 lexus twin cam v8. Displacement is ALL they have in common......Either bike is a poor choice for sand..the wr being a somewhat less poor choice...for sand you need two things...LOTS OF FILTRATION and lots of displacement....Here in Nevada we have a place called Sand Mountain..and many of the bikes around here are purpose built for that mountain..and the overwhelming choice of local sand runners is a kawasaki KX500..thats a monster two stroke, and it displaces the four stroke equivalent of 1000 cc's! (the same size cylinder being filled twice as often at the same rpm).If your new to the sport, and you want to run sand dunes, I would recommend a an XR400 or DRZ400 as a place to start...enough power to get you through the sand dunes and have fun, but not so much as to overwhelm you (the KX 500 is NOT a bike for beginners). Be aware that sand will however RUIN bearings, rings, etc in short order, and it gets into EVERYTHING no matter how hard you try to keep it out. Maintainance to the EXTREME is the only thing that will save your equipment, but even then dont expect much life out of it. That sounds hard and cold, but ask anyone who runs in the sand regularly...thats what you should expect.