Headset Stack Height. Help!

[velohomme]

Maybe I'm over thinking this or just getting old. The difference between length of steerer and headtube is 40mm. Therefore the stack height required for a new headset is 40mm. Correct or not?
The question is will a 41mm HS do the job or does it need to be just under 40mm.
Please don't direct me to Sheldon Brown. I've looked at that website until I'm cross eyed and still non the wiser.
I don't have the old one for comparison unfortunately.
Thanks for any input.

 

[midlife]

You need a bit of space (2mm) for the top locknut not to bottom out so that's 42mm stack height in my book.

Iirc the classic NR campag headset is 42mm

 

[rogerzilla]

That extra for the top nut seal is taken into account in the stack height, so it is 40mm or less.

41mm will usually do the job if there is a locktab washer, because you can leave that out. They never work anyway.

You can also grab an extra mm or so by facing the head tube and/or fork aggressively. Just watch that the crown race seat doesn't get too close to the brake mounting hole.

All the above applies to conventional external headsets. Any other kind is an abomination.

 

[midlife]

This is a good read with diagram on choosing a headset.

https://raleigh-sb4059.com/2015/07/09/sb5464-sbdu-ilkeston-ti-raleigh-time-trial-special-headset/

 

[rogerzilla]

...except the author does all the measurements and then picks a headset with stack height 0.46mm too big for the frameset . It seems to have worked but the top nut seal may well have bottomed out on the steerer.

The A9 isn't a bad headset but it's not actually the rollers that make it so; it's the loose bearing races. Any modern cartridge bearing headset is superior.

 

[midlife]

If the stack height is too big then there's less thread showing and more space for the top nut seal?

 

[rogerzilla]

If the stack height is too big then there's less thread showing and more space for the top nut seal?

You're right, sorry. The risk in this case is that the top nut isn't engaged enough. I wasn't thinking straight.

Generally I try to pick a headset with a stack height comfortably less than that of the frame, and add spacers. The problem comes with early 90s road framesets designed for a Shimano 105 non-cartridge headset, or similar. Unless the builder was thoughtful enough to leave a bit of extra steerer and add spacers, your choice of replacement headsets is limited (Tange Passage is 30.5mm; it's ok). 90s Kona MTBs with the 1 1/8" Impact or Control Center headsets are also slightly tricky but a Tange Falcon will fit, and is excellent.

For bikes with cantilever or centre-pull brakes, you want quite a lot of extra steerer for the cable hanger. I generally leave at least 40mm stack height if I'm choosing a fork to fit a frame.

 

[midlife]

Tange are my general go to headsets, used them back in the 70's and like MKS pedals they have stood the rest of time lol.

Problem for me is that for 70's TT bikes they cut the steerer as short as possible (saving weight) so for a premium brand it's either campg pista, Campag GS or later Shimano pista (sell a kidney).

 

[rogerzilla]

I have resorted to steerer replacement when I really wanted a fork to fit a frame. The Jim Bundy's non-original track fork needed 8mm adding. That 8mm cost £100 but it was worth it