Let me explain with a photo. I think it says it all.
I really wish I could find the picture of me trying to split the log this came from. It was like 40" in diameter and had about 10 wedges in it when I gave up and went to rent the biggest chain saw I could get my hands on with a 24" blade.
If you look closely the fibers follow all the contours. The wood really had that much curl. The distance between the curls is about 7-1/2". That is the biggest curl I have ever seen.
Anyways, I know that there must be some American beech out there somewhere that is good riving wood. I have yet to find it. It appears the European stuff is much more cooperative from what I read. Until I find some that cooperates with my wedges and froe then I will have to stick with my saw. I still follow the fibers as straight as I can.
There has been one advantage that seems clear to me and that is the billets that come out of this wood are practically indestructible. I have put some real pressure on thin mortise walls just to test them. They are so tough and that applies to the wedges as well.
Let me know your experience if you have light to shed on the subject.