Figure out how long your headtube is and find out the stack height on the stem you'll be using(add them together). Then add like 40 mm and that should give you enough of a range for adjustment with the stem. I tend to leave my steerer tube longer than normal for resale or if I decide to switch frames, there will be plenty of steerer tube. I run most of my spacers on top instead of below the stem. Both of mine are at 8 7/8 inches(one 26 & one 29).
The length of the stock steerer tube is not something you need to go by. They do tend to come a little long, so you have room for adjustments. You'll generally find used forks cut rather short - mistake IME.
The length of the stock steerer tube is not something you need to go by. They do tend to come a little long, so you have room for adjustments. You'll generally find used forks cut rather short - mistake IME.
