I know absolutely nothing about this, but out of interest I watched a youtube video of the Gator 400 at work. It would seem to me that by rotating 'top forward' it safely pushes large logs UNDER the drum so no real harm is done if you hit a big one too fast. On the other hand if the drum was rotating 'top backwards' and you drove too fast into a log you would have an almighty explosion as the a log was 'sucked' into the mulcher head faster than it can be shredded. (Sorta like trying to force a baseball bat through a keyhole)