I have a lugged CX/all-rounder frame on the way, will be replacing the 1" threaded unicrown fork with a lugged one (also threaded, same length & rake, no probs) to match the lugged frame. Seller lists head tube as being 105mm. Fork comes in three different steerer tube lengths- 145mm, 165mm and 185mm. Each has a thread length of about 42mm. I'd like to get the 165 and use 2cm or so of spacers, but I'm not sure the threads go low enough on the steerer tube to allow the headset to be installed.

165mm (total steerer length) - 42mm (thereaded portion) = 123mm.

Head tube, again, is 105mm.

So, 123mm (unthreaded portion of steerer) - 105mm (head tube length) = 18mm

If I install a standard 1" threaded headset, say from Tange or Shimano or Campy (fork crown is 26.4) will I run out of thread before the upper cup secures the upper bearings?

Thanks so much to anyone who can provide even a little help.

Spacers, particularly at that height, are a thing of threadless forks & headsets. I don't think I've ever seen such a spacer stack on a threaded fork. Maybe 2-4 mm worth of washers to allow for future headset replacements.

Also, while you can fit spacers between top race and lockring, the top race has to thread all the way down to the head tube.
Will crown race + bearing balls + lower cup + upper cup + bearing balls really eat up 18 mm?

I am no professional bike mechanic but I think that you are going to have to go with the 145 mm tube because you will not be able to get the upper bearing race to screw down far enough with the 165 mm tube and only 42 mm of threads.

You probably can't use the 165 because although the headset will take up about 37 - 45 mm (stack height) the top race must be able to screw down sufficiently. There's no way we can tell you for sure - why don't you just measure the amount of threads used on your current setup? If you have a good 5mm of leeway with the 165 then it technically should work.

That being said, the 145 is a much better fit - depending on the headset you choose you may not need to cut the fork at all. It is not a good idea to raise the fork that much unless you have determined that will work properly for you as far as fit. It's best to adjust fit horizontally before going higher in front, as that changes weight distribution more than it does reach.

Now you have. It's not so unusual. You can see more on the Rivendell site. It gives extra support to tall stems when the goal is to get the bars up higher.

There's just about zero benefit to using spacers on a threaded headset. Obviously the threads have to extend beyond the headset so the threaded upper cup can fit. That means you need about 1" of thread below the top nut of a typical headset. But there's a second requirement, and that's that the stem extend into the fork beyond the threaded section of the fork because the depth of thread is roughly half the wall, and the steerer needs the stem to carry stresses below this weakened area. How far beyond the thread is necessary is hard to say, but figure 1/2" at a minimum and up to an inch desirable (more than that won't help).

So if you measure the fork very carefully and have the thread end just below the upper race, you might be able to add 1/2" of spacers under the locknut, but that's about it. If you need more height than a typical quill stem affords, you have a few choices.

1- use a stem with an obtuse angle so the forward extension rises gaining you more height.
2- use one of those "tall boy" stems - though, IMO, they tend to be pretty crappy.
3- if you're buying a new fork anyway, go threadless which will afford some more choices, and the ability to add up to 2" of spacers, but don't forget that this won't net you much because you lose the 2-3" of height that a quill stem has above the headset. One nice thing about the threadless option, is that there's a nicer selection of quality rising stems (any mounted with the smaller angle on top.

Before spending any dough, take the time to figure what you're trying to achieve (desired handlebar height) and use this stem calculator to see how the various options play out.

This is a potentially dangerous arrangement. The spacers may improve rigidity for the stem, but do nothing for the fork. They also distort the minimum insertion calculus, making it possible to fool yourself into believing the stem is deep enough when it isn't.

For the system to be sound, the bottom of the stem must extend beyond the lowest thread in the steerer by 1/2-1" to avoid breaking the steerer. Plus with the added leverage, it's important that the stem extend well below the upper bearing, otherwise the steerer becomes a cantilever structure, something it isn't designed to be.

Of course it's possible that this particular bike meets all the conditions, but it's impossible to tell from the photo, and if the stem is only inserted to the 2-1/2" minimum insertion mark, it probably doesn't.

Now, to me that setup is just plain ol' ugly. I can sort of abide with the huge shiny lump making up the top half of the headset. But such a tall upwards part of the stem, and then a forwards protrusion that's horizontal at best.
It's like they've put extra effort into putting a sharp angle pointing directly towards the rider's crotch/abdomen - for no practical gain.

But what to expect from a bike featuring a utility-oriented front basket but w/o fenders....

Nice cork grips though.

That stem is very long and it's inserted deeply. It's a fillet brazed city bike stem from Belgium. I don't feel threatened by that "sharp angle".

No, spacers don't reinforce the fork steer tube. What a ridiculous thing to say! The extended steer tube does reinforce the stem, though. I'm sorry you don't like the bike. Fortunately, you don't have to ride it.

There is no room for fenders, but I don't need them. It rarely rains here. Some of my bikes have fenders, but they're just for looks. When it does rain, the 39 year old bike stays home. I built it for trips to the farmers market.

That's the key. As long as it's going 1" or more below the upper headset bearing, and beyond any threads, (whichever is deeper) it's mechanically sound.

After that the only thing that matters is that you're happy with it.

I grew up in your neck o' the woods. I used to take the top off my Jeep in April and put it back on in October or so, and I don't recall the interior ever getting rained on.

The only thing that could make that set-up cooler, is if it was a lugged stem.
I like the high bars thing, which is exactly why I just bought a Rivendell Bleriot.
BTW, how id you mount the bell right up against the headset like that? That's what I wanna do, but don't know how.

Bike Shop may have a steerer tube thread cutting die, to cut the threads further down.

One of the headtube spacers is probably tapped for the bell to screw into. Elegant solution.

Okay, frame arrived last week and fork got here this morning. The original fork's steerer tube is only 139mm, so I went with the 145mm steerer on the new fork instead of the 165 I was considering. I was hoping against hope that the crown race on the stock headset would be a match for the new fork's crown, but it isn't. The old crown race drops onto the new crown and is very loose. That means the old race is 27.0mm JIS and the new fork crown is 26.4mm ISO. Now I have anorther problem. I'm willing to buy a new headset (the stock one is a bit... unrefined), but I have no way of knowing whether the head tube of my frame (early 90s lugged Bianchi Advantage hybrid) accepts 30.0mm JIS cups or 30.2mm ISO cups. That's a measurement I don't trust my LBS to get 100% right.

I'd rather not try the pop-can shim. Should I:

1) try to find a 26.4 crown that looks like the one on my old headset? How close must the crown be to the old one? The headset itself is a very simple steel job, upper and lower bearings are identical, 16 bearings per cage.

2) Buy a JIS headset from a company that makes indentical JIS and ISO headsets, try to press-fit the cups into the headtube (if they go in easily, it should mean that the headtube is 30.2 and so I can just go and buy the ISO headset of my choice). If they don't go in easily, then the headtube is 30.0mm and I need to buy a 26.4 crown from a matching ISO headset.

Just get a new ISO headset with the appropriate stack height (you haven't trimmed the fork yet, have you?), mill the head tube to ISO dimensions and install the new headset.

No, haven't trimmed the fork, don't plan to. I need to add a cable hanger in there somewhere anyhow, which will take up about 3-4mm. Is this milling an expensive idea?

Probably about $20 to do just the head tube. Maybe a few bucks more if you have them install the headset. If you buy the headset from the shop, they may be inclined to give you a bit of a discount.