Minimum depth for quill stem

[BigDaddySmooth]

Fellas,
What is the minimum depth for the quill to sit safely inside the headtube? Thanks.

[ultraman6970]

Depends on the manufacturer an model, there is always an insertion mark... there is no thumb rule on this.

If you go too deep and the frame is too small you can risk the stem get stuck in the tappered riffled reinforcement at the bottom of the fork, obviously if the fork has that.

[oliver1850]

I checked 10 or so handy ones. Most were in the 60 - 70 mm range from minimum insertion mark to the end of the quill (not counting the wedge). Cinellis I checked were less than most others, around 60 mm.

[EricEstlund]

The minimum insertion on the stem is related to the diameter of the part (odd CPSC implementation), and is not necessarily tied to the safe insertion for a given frame and fork.

To play it safe I recommend making sure that the wedge is at least as deep as the center of the top tube (preferably as deep as the bottom of the top tube). I like it to be that deep regardless of how many spacers appear between the headset lock and adjusting nuts.

Just as an example- typical upper stack height is in the 25mm range. Take that 25mm, add about 7mm-9mm of upper head tube extension for older lug styles and the 25.4 of a traditional top tube and you get a minimum insertion of 57-59mm. That's pretty close to the 60 on that Cinelli stem.

[Louis]

I remember hearing or reading somewhere that you want the wedge to be far enough away (I guess below, because above means that you have quite a few spacers) from the upper headset bearings that they won't adversely affect the races, but I have no idea if the wedge really is strong enough to distort the steerer tube and do that.

[EricEstlund]

I remember hearing or reading somewhere that you want the wedge to be far enough away (I guess below, because above means that you have quite a few spacers

You defiantly don't want the wedge to be gripping above the cups. That would mean all of your expansion AND all of your bending force is acting on the threaded part of the steerer- firmly a no-go. It also means you would bairly have the wedge inside the fork.

Getting it below the 25mm of stack and 25-37mm of skirt is a good idea (though I'd still go lower). Not because of bulging the un-threaded steerer so much as taking bending load off the upper portion of the threads.

[Louis]

That would mean all of your expansion AND all of your bending force is acting on the threaded part of the steerer- firmly a no-go.

I've never seen a shear and bending diagram for a steerer + quill stem, but I suspect that a fair amount of bending is happening above the headset anyway, since the side of the quill presumably bears up against the ID of the steerer at the top. However, I agree that the lower you have the bottom of the quill (preferably well within the head tube) the better off you'll be.

I've never heard of a threaded steerer tube failing, but it's not impossible. The thing is, unless we're talking about a 250 lb rider yanking like crazy, the forces involved are pretty small.

[Chance]

I've never seen a shear and bending diagram for a steerer + quill stem, but I suspect that a fair amount of bending is happening above the headset anyway, since the side of the quill presumably bears up against the ID of the steerer at the top. However, I agree that the lower you have the bottom of the quill (preferably well within the head tube) the better off you'll be.

I've never heard of a threaded steerer tube failing, but it's not impossible. The thing is, unless we're talking about a 250 lb rider yanking like crazy, the forces involved are pretty small.

You are right that much of this bending has to take place anyway. Obviously if you insert a quill deep down in steerer the bending load is reduced some but your assumption about reaction loads has to be correct. The wedge keeps the quill from rotating and moving up and down, but the rider's weight causes a bending load that has to be mostly resisted by top and bottom contact points. The more you spread the two points apart the lower the bending moment through the threaded part of the steerer.

Not sure that loads have to be low though. With minimum insertion in the 6 to 7 cm range (a little over two inches) and the rider resting weight as much as 8 inches or so in front of quill when riding on hoods, there is a lot of leverage being applied. Threadless seems a lot better to me, but if using a quill a longer one would be my personal choice.

[khjr]

Rivendell made some mention of this in an article on their website (not sure if it's still there). Their interest in the topic was likely driven by Grant's advocacy of a high stem position relative to the saddle. Grant claimed that, in his travels, he was aware of many steerer tubes split by both the wedge and expander cone style stems when the bottom of the stem (where the cone or wedge is) was in the weak threaded / slotted region of the steerer.

There are some long quill stems, such as those made by Nitto, which help to reduce this risk if you want to get your bars higher. The Deluxe version of the Nitto Technomic is moderately long and reasonably attractive.

I also make a practice of filing down the leading edge of the stem wedge so that it doesn't dig into the steerer.

[Ken Robb]

There are some long quill stems, such as those made by Nitto, which help to reduce this risk if you want to get your bars higher. The Deluxe version of the Nitto Technomic is moderately long and reasonably attractive.
.

Nitto -17 quill stems can be 190mm or 225mm. Their Dirt Drop and Periscopa models allow even higher bars but they lack the traditional look.