I've never seen anything remotely like that.

No bearing is set it and forget it, that is how you run into problems down the road, every bearing ever made needs some sort of check and lubrication and replacement at some point maybe no lubrication for the solid lubrication bearings but any bike I have ever seen will need bearing service at some point. It is just the nature of moving parts bearings are finite. Maybe someone has an application where they could last forever but not for a bicycle realistically unless you don't ever use it.

I think you are being just a little bit alarmist here.
I did this very thing when I was building a bike for myself during the Covid shortages and threadless forks and headsets were unobtatium.
I left the steer tube full length and clamped on a threadless stem.
I understand the concern about the minor diameter of the thread possibly compromising the strength of the steer tube but I regularly inspect the inside of the tube with a borescope and no sign of failure so far,
https://cimg1.ibsrv.net/gimg/bikefor...b69af0626.jpeg

https://cimg3.ibsrv.net/gimg/bikefor...34db19b58.jpeg

OMG, every motorcycle made after 1975 is like that Or threaded outside or threaded inside etc etc.3 ways to secure that area. Bearing, then dust seal, then lockring #1. Then lockring #2 then triple clamp. Then nut/bolt locking top triple clamp to the steering stem (yes that's what motorcycle terminology is). Here.
https://cimg1.ibsrv.net/gimg/bikefor...ab14a7e61a.jpg

The quill is the part of the stem that wedges inside the steerer - motorcycles don't have those.The top-race-to-steerer thread isn't fully engaged, it's easy for the top race to fret against the thread on the steerer, damaging it or loosening the locknut. If a threadless headset comes loose when you're out on a ride you only need an Allen key to adjust and lock it. Quill stems are also a problem, they're only tight by the wedge at the bottom of the quill, the part that emerges from the headset is just a sliding fit, but that's where a sprint will stress it.
The stem clamps the steerer, and locks the compression ring which holds the top race centred. The screw on top of the stem is only used to apply preload to the bearings before the stem is clamped.

I agree with this paradigm. I've been building and modifiying motorcycle suspensions for 20 yrs. The way to keep the steerer tube from tearing apart in this case is to run a bolt from top to bottom and secure it with a washer and nut. So the little friction star is replaced by a longer bolt and a nut and washer underneath the head tube. Like so.
https://cimg0.ibsrv.net/gimg/bikefor...7fa31e4906.jpg

Remember this is on a motorcycle raked at the triples. So scale it to the right size. The idea is to bypass the shear force on the threads of the steerer tube. Run a long bolt that instead of going to the star that is pressed in to the steerer tube - there is no steerer tube and the bolt runs through a big washer and nut under the lower side of the neck tube.

You said welded. There's nothing welded.

BTW I was racing motorcycles probably before your father was born. Worked as a mechanic for years.

I would say you were optimistic and cavalier with your safety. Steerer threads are normally reinforced on the outside by the locked portions of the upper headset and the quill inserted into them. You have managed to take a steerer - which is essentially full of spiral cut, sharp bottomed stress risers, create two compression edges on them at the top of the HS and bottom of the stem, removed any internal reinforcement a quill brings, and then put extra forces on the part being pinched by the stem.


People always seem pretty pleased to report the super dangerous mechanical things they've done, but maybe you should hide this sort of bad decision and just thank God it didn't end badly.

I assumed that based on his continued use of the term stem when there was no way he was referring to a stem. I had asked him to clarify that earlier (#3) which he didn't do and was just expressing my continuing confusion.

Not a chance. Cos you'd be 92 and that is if you were born on a race bike. I also have been a race mechanic and I am in my late 50's. I have been modding suspensions and have done over 30 FE swaps in a process I perfected, as well as build a 9 degree raked cheater chopper that handled better than original.

https://cimg7.ibsrv.net/gimg/bikefor...c5ba412ced.jpg

That is a suzuki savage. A bike that handled like crap with ~9"shorter wheel base and 9 degree+ less rake. This bike when I was done with it handled like a well ... schwinn. Eas it heavier - yes. However it would completely convince you otherwise if you were to ride it. You'd swear it lost 100lb, when it likely gained 10-15.
I will say 1 thing. I am not likely to build a light weight bicycle that does anything better than the original. Because I didn't do that on motorcycles either. But I will be able to build one that works for my liking.

As for being welded - a Suzuki GS500 as well as many other bikes have welded top triple clamp thread bosses into the steering stem.



https://cimg2.ibsrv.net/gimg/bikefor...309e4f8f74.jpg

And that same bike is still standing in my driveway now, 15 yrs and 15K+ hard miles later.

Steerer tube to a bicycle is called stem in motorcycles. It's called steering stem to be precise.

I'm not explaining things in bicycle parlance yet. And this old friend of mine and I had a discussion a couple decades back. The TLDR is ... I told him "car mechanics make the worst motorcycle mechanics" and he, being ~15 yrs older than me replied ... "I dont know about that but motorcycle mechanics make the worst car mechanics". That likely applies here.
I also once famously said ... Bicycle tools are the same as any other set of tools if you ground all of the tools in 1/2.

Threaded headsets and steer tubes are more difficult to adjust; The threads are not "zero backlash", they have slack. If you screw the top of the headset down, barely snug with the bearings, then tighten the locknut, it will push the top cup down further (the distance across the thread slack) and be too tight. So you back off the locknut, back off the threaded cup just a bit, tighten the locknut again and see if it's adjusted correctly. Repeat as necessary.

With a modern threadless headset, you assemble everything but leave the clamp for the stem around the steer tube slightly loose. You tighten the top bolt (connected to a star nut inside the steer tube) to torque spec for the headset, then tighten the stem clamp bolts around the steer tube. Perfectly adjusted. Done. You can also adjust the headset in the field (like on a long tour) without the need to carry two threaded headset wrenches, I think 32mm across flats, bulky and heavy.

He's right. Danger Will Robinson. The difference is this:

With a threaded steer tube and headset, normally, very little threaded portion is left sticking above the headset (which is why it's usually a "cap nut" there), the rest is the smooth quill. So primarily, moderate tension loads in the area of the threads on the steer tube, which it is designed for.

Using a threaded steer tube that sticks way above the headset, with threads just above the headset, imparts *greatly* increased bending moment on that steer tube, with the threads acting as stress risers. High probability for fatigue crack with *rapid* progression to what is known as "catastrophic failure", meaning total and without warning.

With an unthreaded steer tube sticking way above the headset, not a problem, within design limits; No threads to act as stress risers, and a steel steer tube can take some bending loads. Within limits. The fork maker typically specifies the maximum length of steer tube allowed above the headset.

How is that different than what I described?

It's not, at all. I was just trying to put it in terms they might understand, with a few specific examples, especially how what they want to do is different from the intended load conditions of a threaded stem. But you are 100% correct in your warning, well done.

I get it. Threads cause a starting point for a crack and this will not bend and give you any warning, it will just snap like a pretzel. I get it, I am steering away from it (no pun intended :lol:

Good man. The term Catastrophic Failure is an actual engineering term, with the potential for it strictly avoided, and/or having a redundant design to mitigate that, take the load while providing warning. Like safety chains on a trailer hitch. But there are so many things on a bike that are "single-point failure", no backup.

The more I think about this, the better option is to do what I have done before on my cheater chopper (motorcycle).
There is enough room between the treaded part and the stem for me to run an inner tube as a spacer. Then I'll use a long bolt ~8mm and 2 large washers and bolt it top to bottom. That serves the same purpose as a quill type insert, but instead of friction load transfer to the steerer tube and then the neck it actually bolts them together. That way even if the steerer tube cracks at the threads the bolt will keep it from coming apart. Rubber will avoid loading 1 spot hard too. Not gonna win any beauty contests, but I'll post the result if I ever get around to that way. I have various parts I dont even know about lying here and there. Lets see.

If I understand this correctly (I may not), the "inner tube" you are talking about is a steel tube, that you will load in compression via a long 8mm bolt with large washers on each end, I would imagine between the top of the threadless stem, and the underside of the steering tube at the bottom of the fork crown. I could have that last part wrong.

If the long steel tube is loaded only in axial compression at the ends, it may slip sideways or fore/aft on the washers. Or slip in torsion on the washers. Each could cause steering loss.

The long steel tube will be much stiffer in bending than the long bolt, but all bending load on it (like when climbing standing, pulling hard on the handlebar) will be transmitted via the narrow top and bottom end of the tube, into the washers, which is a much smaller load area, versus clamping to the side of the tube like a threadless stem normally does. If that slips, or the threaded stem cracks, and all load from the handlebars goes instantly into that very long 8mm bolt, the bolt will probably bend, perhaps not enough to break, given that steel is very malleable provided it is not brittle-hard high strength steel.

It would sure seem more sound, as well as dirt cheap, to buy a threaded-to-unthreaded converter as someone noted above (post #3), with expanding quill on the bottom to go into the threaded steer tube, and a stepped-larger diameter on top to clamp the threadless stem to. The holy trinity of design, "Lighter than air, stronger than steel, cheaper than dirt."

Again, I may not fully understand your intentions. But those converters are so cheap, plus will look nice.

At least, if you assemble what I think, any drawbacks of it should be self-evident the moment you try to put any serious steering torque or climbing hand moment into the bars. I've heard people make money off these sort of videos.

Inner tube is a bicycle or motorcycle inner tube that I will stuff between the stem and the threaded part of the steerer tube.
Then a long bolt secures the stem to the frame with a nut and washer under the neck.

I had entertained the thought for a micro-second, that you meant a tire tube, given that you used the word rubber in your text, but dismissed that as my being mistaken. OK, I withdraw, I'm gonna just have to sit back and watch on this.

I'm not saying I'm doing that. Mainly because my parts bins are largely now unknown to me. Where will I find a long 8mm bolt ? But I am saying its a way of bypassing the hard impact loads on the thin threaded steerer tube.

Hard impact ("shock") loads are important, but I think the most significant loads in this case, will be when you are climbing hard standing on the pedals, and alternately pulling upward on each handgrip on the bar, so fully reversing bending loads at the stem. A wide flat bar will be worst in this regard, greater moment for the same pull. Shock loads I think will happen with downward force on the bars when pedaling seated, with the front wheel hitting a pothole in the road. The rubber between the threads and the stem clamp (if I understand correctly), that will act to cushion the tops ("points") of the threads, but do nothing to lessen the stresses at the bottom of the thread valleys, for the threads exposed between the stem clamp and the headset cup. Again, that's if I understand this all correctly. I'll watch what you build.