This thread is a sort of a follow-up to an earlier one: http://www.thumpertalk.com/forum/showthread.php?t=788939 I did the front tire testing during the desert off-season, and the heat and wind took turns for a while keeping me from doing getting much time in out there. Since then, I've run an MX31 (120/80x19) at two race weekends, and an MX51 (110/90x19) one weekend. The MX31 performed pretty well, but overall was no better than a 952. This was something of a surprise to me, but nevertheless true, and especially so on the harder surfaces. The MX31 had a tendency to slip out under power on harder surfaces, and didn't bite well on them in a straight line compared with the 952. The big surprise was in the sand. The 952 has significantly more straight line traction in fine sand than the MX31 did. The MX31, on the other hand does seem to hold corners and side hills in the sand somewhat better. The tire also showed a disturbing amount of wear for the few times it's been run. This was more a matter of the drive side block edges rounding over than of their wear shorter, but it was still pretty significant, and it's definitely wearing much more quickly than a 952. Overall, I'd say the tire is better suited to mud than sand, and probably a good choice for soft to intermediate soils that have a bit more moisture in them, not so good as a desert tire. The MX51, by contrast works exceptionally well. While I wasn't able to get to the dunes with it, there was some fine sand on the course, and the tire did very well with it. There were also several very loose, silty hill climbs, and the tire was impressive under those conditions, pushing hard versus digging in, even in the powder. Traction on harder surfaces was excellent, and as Wiz636 noted in the other thread, the tire holds very well exiting corners under power. The course included a lot of very rocky terrain, also, and after close to 100 miles of riding over two days, the tire literally has barely any wear on it. The drive edges of the knobs are not even significantly rounded over, and in fact are hardly roughed at all. The wear, in fact, seems at this admittedly preliminary point, to be somewhat better than even the 952 rear. The MX51 is so superior to the MX31 in the rear as a desert tire that it has me wanting to try the front now, in spite of the fact that the MX31 front has been my favorite front tire up to this point. I'm impressed.