threadless stem/steerer question

[Drw]

So i know that on a standard threadless stem, you want the steerer a few mm below the top of the stem, but im wondering about a stem like this 

https://store.somafab.com/niuicrthst26.html

since the clamp is lower, is it safe to have the top of steerer further down? like 10-15mm below the top of the stem?

(The further i get into this project, the more i really appreciate quill stems.)

[iamkeith]

Thanks for bringing that stem to my attention, even though i only have a speculative answer for you:

By all means, make sure the steerer extends well past the clamp slot relief hole as a minimum, and preferably at least half way up the intersection of the horizontal extension tube. I think there would be some levearage stress otherwise, that could lead to cracks.

I've cracked the clamp on a two-bolt threadless stem where the steerer didn't extend far enough past the lower bolt. Slightly different situation... but similar.

Don't forget that you'd need a long pre-tension cap bolt to reach the star nut. Don't cheap out on the grade of that, or it could shear.

Agree on the threaded wish.

[iamkeith]

If you read Soma's description of that and the similar stem, it says "reduces the need for spacers," not "adds height to a too-short steerer." So it seems like it's an aesthetic thing mostly. Sure would make sense if they provided some actual instructions.

[Bill Eberle in Columbus, Ohio]

If you're asking because you're about to cut the steerer I'd suggest that you do so leaving as much as possible remaining, i.e., 1-2 mm below the top of the stem. A too short steerer could affect the bike's saleability later.

[iamkeith]

This might a safer bet, though sold out from here:

https://global.bluelug.com/nitto-mcr65-stem-silver.html

If you don't need the removable faceplate and 31.8, Riv has a similar one. I have one and think it's great:

https://www.rivbike.com/collections/stems/products/nitto-hiriser-25-4-1-1-8-threadless-stem-16252

Then again, the current crop of faux LD stems often have only one clamp bolt. I wonder if they come with instructions that say anything about minimum insertion:

https://velo-orange.com/products/cigne-stem

[Coal Bee Rye Anne]

I’ve debated the exact same question... just in relation to an alloy FSA Metropolis stem with the tall stack and single pinch bolt. It fits perfectly on a previous build with threadless fork (protruding a few mm above steerer and stock compression bolt reaching as designed) but when I tried to fit a spacer with bell mount it pushed the stem up further than I was comfortable with and the stem being fully hollow inside revealed what then looked like too little structural support for the hollowed out extension. That was just my uneducated observation so I removed the bell and spacer to drop the stem back down flush with headset. I know VO and Crust had stated min/max steerer heights for their cromo LD stems... not sure if VO states a minimum insert for their similar tall stack alloy threadless stems though. Should take a look and either way I’d assume the cromo versions may be a little more forgiving without being completely hollow like the alloy variety I have.

[Coal Bee Rye Anne]

VO tall stack states steerer should be no greater than 15mm below top cap:
https://velo-orange.com/collections/stems/products/vo-tall-stack-threadless-stem-31-8-rise

[Drw]

Interesting.  The steerer is just a hair shorter than i wanted for a normal stem, yet too long for a super big riser stem. i guess im trying to avoid having to cut it down just to fit a really tall stem. 

That VO one is similar and aluminum, so if 15mm is ok for it, i assume 15mm would be ok for a steel nitto version too. 

[Coal Bee Rye Anne]

And then there’s this one with pinch bolt up top!
https://global.bluelug.com/fairweather-ui-7-integrated-stem-silver-11892.html

[Benz, Sunnyvale, CA]

On Tuesday, October 23, 2018 at 10:03:59 AM UTC-7, iamkeith wrote:

 

Don't forget that you'd need a long pre-tension cap bolt to reach the star nut.  Don't cheap out on the grade of that, or it could shear.  

I don't believe that's true. It's entirely fine to use a weaker pre-tension cap bolt in a threadless setup. That bolt serves only to pre-tension the headset (with very light torque), before the stem's steerer clamp bolt locks in the setting. Once the steerer clamp bolt is tightened, one can even take off the pre-tension cap bolt entirely. As a real life example, I happened to have a few aluminum M6x40 bolts and they worked fine for years as pre-tension cap bolts.

Back to the OP's question, if I remember correctly, the advice about leaving a silver of spacer on top of the stem is to 1. ensure the headset can be preloaded correctly, and more importantly, 2. the stem clamps onto a relatively strong part of the steerer and does not pinch the end. For the stem that the OP identified, I can't help but wonder if, additionally, the stem designers intended the steerer to reinforce the "quill", meaning overlap is expected. In any case, since stems are critical components of a bicycle with dire consequences for failure, if it were me, I'll ensure I have maximal overlap (meaning maybe cut steerer to be 5mm below top of stem), or ask the seller for more info.

* All bets are off for carbon steerers, however. Nevertheless, this being the Riv forum, I certainly hope that's not a topic we should entertain! ;)

[Lum Gim Fong]

3 good things about having threadless steerers:

1. Easy to remove and reinstall fork should you need to.

2. It gives you the opportunity to buy and install a gorgeous Nitto lugged stem that Nitto makes for threadless steerers.

3. It gives you the perfect excuse to buy a Rivbike for the more easily height adjustable threaded steerer setup.😀

[Drw]

So i did get that nitto stem and put it on last night. The part i forgot to mention is that im using a shim to go from 1-1 1/8. So the steerer tube ended up being about 1cm below the top of the stem (which seems plenty close) but the shim is only 4cm tall, so it sits considerably lower than the top of the stem (which is about 7cm tall). a taller shim would fill the gap, but i dont see any online that are very tall. Is this even a problem? thoughts?

[Benz, Sunnyvale, CA]

With the shortish shim, the effective steerer tube length ends where the shim ends, and the part of the steerer that protrudes until 1cm from the top of the stem doesn't count. From looking at the picture you've provided, we know that the shim is tall enough to ensure the stem is clamped at least adequately to the steerer (and won't pinch, which is unlikely for a steel steerer anyways). Thus, the same question applies: does the stem require the steerer to be part of the structure, or is 3cm of unsupported and cantilevered stem OK?

[Coal Bee Rye Anne]

I certainly can't speak from an engineering perspective but I think I'd personally want that 3cm gap to be filled.  Although I'd feel ok in the short term with the stem and steerer both being steel if just testing fit with a few short rides and I'd likely go ahead and ride it as-is before going to the trouble of finding or making my own full sized shim.  But if deciding to keep that setup longer term I try to get a properly sized shim to fill all the space. 

I have a trashed steel frame from which I already cut and filed some small shims from the middle of the downtube for a threaded 1" headset that needed some space taken up.  It's seamed tubing and I'd probably just try cutting a single full length 7cm shim from that same downtube and cut the split at the seam to help eliminate some filing and sanding.  If I didn't have this trashed frame I guess cutting down another 4cm alloy shim to the required length is the other logical alternative.

I'm not necessarily opposed to such hacks but I'd have some reservations with that excess air space between stem and steerer.  For some reason I feel like I'd be a little more confident even if the steerer itself was a bit shorter if both steerer and stem were a matching 1" spec.  I have no educated basis for this and ymmv, of course.

Brian Cole

Lawrenceville, NJ

[Joe Bernard]

I agree with Brian for the same reason I think carbon forks are a bad idea: The steering area of a singletrack vehicle is simply not the place to cut corners and take chances. Fill that gap!

[Drw]

Ok but is filling it with a 4cm shim + a 3cm shim acceptable? I don’t think they make one long enough for the whole thing.

[Benz, Sunnyvale, CA]

Try a seat post shim of the same thickness, such as this, and cut it to length. Seat post shims are generally 3" in length so you should have just enough material to work with.

[Lum Gim Fong]

Could you just replace with an RBW Carbonomas fork and use a proper stem with the proper steerer length of the Carbonomas?

[Coal Bee Rye Anne]

Ha, of course, a properly spec’d seatpost shim would certainly be the most straight forward. Thanks for sharing! It’s funny ‘cause I’ve previously looked for certain seatpost shim sizes only to find they don’t seem to exist... but never needed a 25.4 to 28.6 like this. Because I’ve kind of given up on seatpost shims for anything other than 27.2 (whether to shim smaller post to 27.2 seattube or 27.2 post to larger diameter seattube) it didn’t even occur to me to look for one at that spec.

[Coal Bee Rye Anne]

I should add that this all interests me because of a tentative 1” threadless conversion of my own.

[Drw]

So many good ideas. The seatpost shim is great thinking.