I have a Peugeot Competition 5000 from '98 or thereabouts and the threaded fork (stem and handlebar in reality) is giving me a headache, but it's got me thinking about bikes from that era. The Peugeot is fairly low-end but a good chunk of higher-endish bikes seem to have made use of 1" threadless forks... so could I save myself from a migraine by getting a 1" threadless headset and fork ? I've even seen people keep the threaded fork and add a 1"->1"1/8 shim but I'm not sure how safe that is ? I may have confused myself with the inch talk as I'm european but I hope I conveyed properly what my goal is

It is also possible to use a quill adapter that makes it possible to attach a 1" stem to that adapter. It is a safer option than using a 1" stem directly on the theaded fork. It does add a little weight though.

If you do decide to change the fork and headset, make sure to have a similar fork offset and trail, to keep the same geometry and handling characteristics.

1" to 1 1/8" shims are perfectly safe on threadless forks. Threadless forks only!

Using the shim on a threaded fork seems questionable, to me. Even if the threaded section is long enough to accept the entire shim, I think the threading reduces the surface area for contact between the steer tube and the stem/shim, ergo, less grip. No issue with threadless fork.

Just my two cents...

I have used stem adapters, threadless stems and then bars on threaded forks with no problem.

In fact, it allows a bit of height adjustment based on the stem you use. Add some spacers below the stem and it looks fine. Other than Technomic types, quills limit the height of the bars.

Advantages
1. you don’t have to worry about stem quill height to make it comfortable, nor is it a problem to change it up.
2. Being able to remove just the bars is an advantage if you like to tinker.

That's where the headache comes in. I bought one of these, but it's too deep and on a small frame it hits the bottom of the steerer tube .. ? and makes the whole setup look silly. Stem height is technically not an issue since I can slide it up and down, but the adapter sits way higher than it. I'm usually not too fussy but this and the fact it hits something on the bottom makes me reluctant to using it. Hence my question!

The headtube is a mere 11cm from what I remember. From what I heard here and there, and correct me if I'm wrong, but during that time they significantly sized down the height of bikes and installed bigger stems to counter that. I'm 1m74 and the bike is supposed to be a 54 as per the part number (VIA6000UFR541C9) but it measures a 52x54 with a 110 stem. Too long for me. That's why I'm not too fussed about this setup and was more wondering about the technicalities of such a fork swap. After checking around online for 1" threadless headsets, I think I will be getting a bike that measures a 54x54, easier than the swap

First, what is the actual issue with the OP threaded fork, stem and handlebar? No reason to go doing a heart transplant, if all that is needed is some antacid.

Phil

I knew I forgot something, I meant on a 1" threadless headset. With a starnut and all.

I've used threadless stems on a couple different threaded forks with no problem.
Same with a threadless adapter.

Another option is the Innicycle threaded-to-threadless conversion headset: https://www.innicycle.com/

I installed that on a recent build so that I could use a wider variety of stems:

Replacing the fork and going threadless is doable, but a few things to be aware of. Choices of headset and stem will be limited vs. current 1-1/8 standard. You will probably want to trim the steerer tube of the replacement fork. It is tricky to make a square cut unless you have good tools. Last thing is you could be sinking a bunch of money into a lower end Peugot. Me, I would be shopping for another bike.

Yep, easy to always revert back to threaded.

I saw that when searching for 1" threadless headsets, costly but very nicely made. I'm sure to get one in the future if I run into this same problem on a nicer bike !

Yep, that's what I was saying a few posts above. Now the headache is finding something not too bad but not too great either . My goal being a mainly road(+city) bike I can use to commute quickly but also that allows me to decide on a whim to bike around the Vosges and Schwarzwald. At least I have a full group mix of 8sp Athena/Avanti/Mirage from it that fits this bill perfectly

Amazing bike, the stem conversion is flawless, just beautiful !!

There are about a bazillion 1 1/8" stems and the shim will put them on any 1" steerer. No Problemo !

This is how I approach many frames without forks now. Find a 1" threadless fork or even tall 1" threaded forks (but do not clamp on threads), order a 1" threadless headset and shim, use modern stem of choice.

One of my favorite builds is this 1984 Bianchi San Remo. I bought the frame alone at a swap meet and had the fork from a tall scrapped 1981 Puch Pathfinder. The color was close to identical and I had enough space for the threadless headset and stem after removing the threaded portion of the fork.

I'm sorry - I completely misread your post. No, it isn't safe to use shims to clamp to threads. The threads will break off.

Some people are concerned about using shims in general, and that was what I was answering.

It is also acceptable to take a tall threaded fork and cut off the threads off to make a threadless fork out of it for a small frame.

Generally speaking, there is normally not enough steerer sticking up on a threaded fork to clamp a stem around it. Which is why I didn't realize that was what you are asking about. Also, the threads will fit loosely in the threadless headset..

Ok, so I reread the first post and got all sorts of confused.
1. Is the problem the stem is too long horizontally? If so, get something shorter like 80? Or 70?
2. Is the problem the quill height on the stem making it too high (so that it is above the safe insertion point?) If so, there are shorter quilled stems ( ITM Eclypse comes to mind)
3. Is there an issue with the fork threads or diameter and your stem?
4. Is the steerer too long so that the headset needs spacers and it makes it look wonky?

Problem with getting a new fork is also the rake and trail of the new fork, and whether it changes the dynamic of the front end.