I was planning on building up an old steel road bike frame using a 1" threadless steerer carbon fork that I had from another bike. I did a test-fit of the parts this afternoon (with the headset installed in the 'new' bike). What I found was the taller head tube in the 'new' bike left me with something like 20mm of gap between the cap (or, top of stem) and the top of the steerer tube. Everything I've found as a reference says this gap should be something like 3-4mm or there is the good ole' "risk of injury or death" factor. Some considerations:

1. In this case, I am using a spacer for the stem (1" tube, 1-1/8" stem), so in effect (or in a sense) the height has been shimmed.

2. The star nut in the steerer was installed rather low. I replaced the cap bolt with a longer one and was able to adjust the headset correctly.

3. The uppermost tightening bolt on the stem are even with the end of the steerer tube (maybe a mm or two below, I guess). The stem feels secure with no apparent distortion.

So, the question is whether, considering 1-3, I've built a death trap. I don't *need* to use this fork and I've got other bikes, etc. etc....it's just for fun, so if there's no way to make this work, I'll think of another way to put all the parts together.

THanks in advance.

You already know the answer: "Too short is too short."

damned modern threadless crap.....meh!

A too short threaded steerer is just as bad so how is threadless different?

A 20 mm gap is WAY. WAY too much. You need a different fork. However, I'm surprised that the upper stem clamp bolt is still over the steerer with a gap that big.

Yeah...I should measure again, but it's no 3mm..... and, btw, I was just kidding about the "modern threadless crap".....I know it goes with the territory when you start treating bikes like Legos some pieces just don't fit together right.

I knew you were.

That's what she said

OK, I've got a good joke that's on that topic but you'll have to PM me if you want to hear it.

sounds like a i have an answer, but for the sake of completion, here's a picture. the gap is 17mm and I am corrected...the upper stem bolt is a few mm above the top of the steerer. I'm assuming the shim adds nothing structurally.

Hillrider hit the nail....er... bolt in his post when he mentioned almost as an afterthought about the upper stem clamping bolt. If it isn't bearing on the upper edge of the actual steer tube by at least 1/2 the bolt diameter then this is a non starter. When I've bodged bikes together like this I want to see the top of the tube up at the upper edge of the upper stem bolt. If I don't get that much or more engagement then all bets are off and I find some other option. In your case a possible option would be to removed a spacer from below and go with a stem that has more rise angle. It may not look pretty or "classical" but if you've got a spacer under the stem that could go in favour of a correct amount of stem engagement then you could "Lego" onwards knowing that at least it's safe. Even if you have to go for one of the Fred like 45 degree rise stems it would allow the project to go on.

Thanks. I'm not afraid of Fred stuff. For the most part, I'm the only one I'm interested in pleasing with the aesthetics. This project was an intended to be a clash of classical & modern anyway...old lugged frame with modern wheels, brifters, carbon fork and flared offroad style drop bars...surely a firestarter on many "taste"-driven cycling message boards...lol. I was looking forward to riding it in my bright safety green jacket my wife gave me for Christmas too! Thing is, the bars I want to run have a 31.8 clamp diameter & I doubt i'd find a quill stem for that.

Back to the topic, it does look like i could use a stem with a shorter stack height (about 35mm would work if I've got my measurements right) and have adequate coverage along the steerer. Anyone know of a stem with a short stack height?

Oh, and it's already with no spacers...so pulling a spacer isn't an option.

Was bored, recently had researched some headset stack heights, came up with this 34mm stack height OS stem https://www.ibikeparts.com/ITM-VISIA-...459723004.html

I wouldn't ride that. But then again it's your face, not mine.

If you're willing to risk it, you could address some of the problem with your upper clamp bolt being above the top of the steerer by inserting a short length of steerer above it.

This is only to stop the clamp tapering off the top of the steerer; you'd still only have one effective clamp bolt. I'd only try it after reducing the discrepancy as much as possible with a slimmer headset and stem... is there any spare head tube / upper lug to remove? Plus, if you'd like a tighter head angle, you could shorten it from the bottom too.

well, turns out I have a stem that's enough shorter to have about 4-5mm at the top. Personally, I like my face, so I'll treat as well as you treat yours...heck, maybe even better, I don't know. Anyway, the short conclusion is the other stem puts enough meet on the clamping section of the steerer to be "safe" so the bike goes on I guess...but without the drop bars I was going to use since they are 31.8 and the stem that works is 26.

This brings up a question...what exactly IS the mode of failure if one were to ride a setup like in the photo? In a way, it doesn't seem like it would be much weaker than a steerer shimmed up say 60-70mm...which I see from time to time.

But, again, as I told a 4 year old today who was showing off his helmet....your head gets more valuable every year, so I'll gladly err on the side of caution.

Interesting idea of shaving the head tube...or, rather, the lug. Is that what you meant? I seriously doubt I'd do that, but it's an interesting idea. Would the heat from cutting weaken the head tube?

For the setup shown in your picture it may well be that on the road you MIGHT never have an issue. It's obviously solidly pinched by the lower screw but the tube only gets up to 1/2 way to the top screw. Then there's your shim. To me that actually hurts the final strength of the joint because it allows the actual stem to work with more leverage and less steer tube engagement.

For casual riding it would likely stay in place. But when you stand up and start levering off the bars while crunching up a hill or similar there's a darn fine chance that you'll suddenly find yourself holding a set of bars with no steer tube connection. And that's the real test isn't it....

For single screw stems I want to see the proper 3 to 4 mm clearnance only for the cap. For longer two screw stems I'm a little more daring but I want to see the upper screw fully pressing on the steer tube at least. If not I may use the stem for a few days but only until I can ride to the bike stor and get one that fits correctly.

What you show with the shim? I MIGHT ride to the bike shop since it's not far and it's all level and if I can lift, tug and lever at the bars in my shop and they don't budge then I would trust it that far. But definetly not for regular riding looking like that.

lol...nothing around here is all level! it felt tight & all, but there is only so much simulated tugging & vibration I could have done with the bike not built and I'm tool old & not nearly desperate enough to knowingly risk it - which implies I probably do stupid stuff every day where I don't even realize i'm taking a risk. The replacement stem is within reasonable spec and no less cludgy looking on the red & white lugged steel frame w/ the carbon fork as the other was. I'll probably try this out & later on migrate this fork to my wife's '87 Cannondale....where a carbon fork would make more sense in the first place. thanks all for the thoughts + feedback.