I usually split my in 1/2 as DarkSoul said,but I always do Hickory in late spring or early summer so the bark peels right off,then I split to 1/4s and then the 1/4 in
to 1/8, I only cut big Hickory 18 and bigger but have cut some smaller stuff and still split into 1/2s. If it looks like is isn't going to spilt right I pop a chalk line 2 1/4
wide from end to end and cut it with my band saw,saves a lot of wood,also as
Eric said I pop the heart wood off as soon as I get it split in 1/4s and it will saw or split much better,usually right down the middle.
You can usually put a wedge right where the heart and sap meet and it will split off end to end sometimes with one lick. Of course their are no hard fast rules to splitting,seen some that you think you will never get split and fights all the way and then another that grew right beside to tough one and it splits like butter,go figure it's wood.
We do between 75 and 100 staves a year for the Classic/scouts and just folks that want to come make a bow so I have cut and splt a bunch over the years. Seems every one is a little different.
Pappy