Do integrated headsets have a zero stack height?
 

Looking at budget frames, I don't want to get a head tube much taller than my current one (125mm) since I'm already on a -17 stem with no spacers. Now, I have a regular threadless headset with the top cap of about 10mm. Does that mean a frame with an integrated headset could have a 10mm taller head tube and still come out the same fit-wise?

Well, the integrated headset will still have a top cap, so it's not "zero stack", per se. Usually though it will be at least 1 cm shorter stack than the non-integrated headset's total (bottom cup height, top cup height, top cap).

Thanks. That gives me a good idea of what I'm looking for.

But then the lack of an external race on the bottom will lower you back down a little. Plus the tire clearance down there seems to be getting less and less. I just went through this same dilemma, and I decided that it's impossible to really know, what with all the variables.

On the other hand KendallF is probably about right. ;-)

I always figured frames and forks designed for integrated headsets correct that stack difference (i.e. larger crown). Otherwise, "lower you back down" would also mean "alter the geometry". For example, lowering the front a little would also make the STA and HTA a little larger, and the bottom bracket a little lower. Someone correct me if I'm wrong.

Well, the geometry as a whole can be altered to account for that. My point (?) is that there are so many parts between the axle and the lowest possible stem position (which is what really matters) that it's difficult to tell without a complete assembly (or detailed specs).

That said, Kendall's rule of thumb is probably close enough.

One more thing: if you're buying a "mainstream" frame, surely you can find someone here to measure theirs (axle to top of stack) to compare to your old frame.

What you want to compare is the total length of the head tube, spacers and headset top section. If a conventional headset is used, the stack height of the headset will be 25-35mm in total, without spacers. The integrated could have a total stack as low as 8mm, but a lot of frames come with a 15mm headset top section.