Or just leave it like it is because it’s designed to be like that. Mine has 5mm less spacers and survived 3 days of Flanders cobbles 2 years ago.

The Zinn insert seems like a bad idea. It is only threaded at the top, so cutting the steerer becomes an issue. The Cervelo tubes had small star nuts inside so you could push them in further for cutting.

3/4" thin wall steel conduit is the same outer diameter. Make your own for $2 a foot!


But I do agree that this should be unnecessary.

Unfilled epoxy provides crush protection but not a lot of tensile strength - you could use glass or carbon chopped fibre filling. A longer steel tube (or aluminium if you prefer) could reinforce the entire stem clamp and headset area and into the steerer below those danger zones. Even if the carbon breaks in those areas the stem is still anchored to the steerer. No I've not done it, I do not own any carbon forks, but if I did then I might - my bad back encourages a higher handlebar position.

It is fun to talk about the ultimate reinforcement for a carbon steerer. In practice though, if installed correctly, almost never break, and when they do it's from a crash or something like that.

It's a bit of a personality test. In the last couple years I've built a deck and shed. Both are more robust than code would require.

I accidentally hung up a carbon fork on the ceiling somewhere my garage door would crash into the carbon when opened last week. The wooden garage door ended up bending in half and the carbon fork just has a scratch.

So they are surprisingly strong. This was just a cheap $65 PROMEND FK-416 fork as well, barely one step above the lowest grade Toseek forks.

That said, I like high bars so I made sure to buy a carbon fork with a metal steerer. So I'm not trusting my steerer to lowest grade carbon.

For me the problem with carbon is that in normal use it's probably fine, but as soon as you crash it, no matter how little any damage may appear, you don't know if there was a void or dry spot in the layup that has now started a crack. Maybe you hit a pothole badly and the crack extends, now you're riding on borrowed time.

I crashed a bike, steel frame, a low speed (but very sudden) fall onto tarmac and there was no significant damage apparent. Later I noticed the entire frame is twisted, and a pedal broke its spindle a few weeks later. Now I'm not worried about the twist, if I was using that bike now I would straighten it and not worry about it failing, but carbon is more likely to act like that pedal - doing fine, doing fine, sudden catastrophic failure.

I see ultrasonic crack detectors start at around $1,000 now - if I was working with carbon I would be tempted just to be able to say "there are no signs of internal failure" rather than "it's tricky stuff, you just can't tell" or "send it to a specialist, it's $200 plus shipping".

It’s really not that fragile.