I'd that a star nut in a carbon steerer? That's a big no no.

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What's your CdA?

Looks like an expansion wedge, should be good

Do you, or did your friend, ever put it on a plane? I've sat on a plane, looked out the window and seen them throw and drop baggage totally carelessly. If a bike was dropped and took a big impact on the bars or top of the stem I'm not sure you'd see much evidence.

I'm too lazy to search, but I posted back in 2014 about my 2012 TMO2 cracking at the steerer tube during a race. It wasn't a full break like yours. Just halfway through and the handlebars were rocking up and down. The idiot fitter picked out a ML for me and then put a 130 stem on. I had always thought it was from too much weight cantilevered on it.

Most importantly, I'm glad you're okay.

Where is the headset bearing dust cover? The little conical spacer before the spacers or the stem.

It fall off from the pictures or ride?

That shouldn’t be excluded.

I’ve got nothing to add except....”OMG!” “WTF?!?” and “Glad you’re ok”
Thats seriously scary

What is the structural importance of the conical spacer?

It may have been the 'slammed' bit that did it. Particularly if the bearing dust cover was removed or one with less stack than the OEM part was used.

Ever since Hincape broke a steerer in Roubaix most manufacturers have stipulated a minimum height between the frame and stem. Many of them now have 15 or 20 mm bearing dust covers to ensure sufficient height to allow a longer length of steerer to flex under the load.

I remember reading up when I had my steel steerer cut Trek recommended a minimum of an ~1/8” spacer above the stem for some structural reason.

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Madison photographer Timothy Hughes | Instagram

Are you talking the cone bearing washer/spacer? It looks like that is missing too.

Maurice

Difficult to tell without seing in the flesh. But something I noticed, and something else to comment on..

2nd and 3rd photo. There looks to be a circumferencial groove / score, maybe where a spacer had been at some time previously ? If the same sort of score was also at the fracture line, I'd not be surprised. Score = stress raiser
Why is it there ? Unsure. Several possible reasons...
- spacers having sharp edges
- have twisted the stem vs steerer at some point, maybe with some load on the cap or stem bolts eyc.
- Headset loose at some point ? So subtle rocking back/ forth/ sideways could cause a spacer to dig in when the steerer is flexing.

Other thing. The expanding wedge. If that's done too tight, it can cause cracks / split in the steerer tube. (Remember thay is only there to take the slack out of the headset - not to hold the stem in place (the 2 sideways bolts in the stem do that).

I'm aware of stories of split steerers in the UK from 1 type of headset that used a neat expanding collar system rather star fangled nuts (on MTBs). But if overtightened could damage the steerer (the manufacturer made the bolt from AL and 'necked' it so it would break if over-tightened. But yours looks like a steel bolt that could excert huge force onto the steerer tube via the wedges.).

Very glad you're OK.

i'm gonna go with 3 years of nasty, frequent, and saturating sweat corrosion... ;)

Thank you for the replies everyone. Trying to answer everyone here. Here are photos of my front end from earlier in the ride. I did have a conical spacer the stem sat on but lost it in the crash. It was slammed when I bought it with the stem angled downward. I flipped it to angle up after a year for comfort purposes. The expansion wedge was installed by a mechanic I trust back in March because the previous one became loose and retightening properly didn't work (forget what failed in it). I did ride it like this when the headset was loose but the spacer setup has always been the same. Did that do me in? Could the big angled stem play a part?

Flew with the bike once in a hardshell box but I had the bars removed from the frame. Used bikeflights once as well but same story.

If I can find a new fork I will definitely be leaving more space and switching to a flat stem.

I'm no bike fitter, but this is a bizarre setup; I'ver never seen a stem with that much of an upward angle, also weird stem bolt orientation. What specific brand and make of stem is it?
As others have said, I have never seen a bike with no spacers whatsoever under the stem.
Likewise, this looks like a bad fit, this steerer was cut way too short for how high you have your bars, and/or this frame is too small for you and/or too aggressive a geometry for the fit you have.

I think it had something to do with your weird setup put an unusual force/moment on the steerer. Did your steerer tube go the full length of the stem (you have no spacers on top either.

Was this a used bike when you bought it?

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Yes, purchased from a friend who was the original owner.

The stem is Bontrager. Original owner got the stem to get even more drop. I needed more stack and with the tube cut flipping it was my only option. Weird looking, yea, but I am very aero and my power in aero is still good.

I guess what I'm saying is, a better option would have been to not buy a bike that with a stem cut that short (this was an option you did not choose). As I said (and I believe others have also commented), that stem was cut so short that there were zero spacers above or below the stem.

1. I have never seen this; doesn't mean it never happens, I've just never seen it and would never set up a bike with no spacers.
2. It would seem wise to have at least 2 cm of excess in stem (absolute minimum) to allow some basic position adjustment without having to buy a new stem every time.
3. Maybe someone can weight in on if there would ever be any reason to cut a stem this short? Is there any kind of spec on the fork install about min/max use of spacers that your setup violates (besides the common sense reason of having some adjustability).
4. I believe the combination of cantilevering the stem at the very end of the steerer tube (no spacers), the high angle of the stem putting an unusual moment, and some kind of potential wear point at the headset interface (related to no spacers or something weird in how this interface was set up on your bike) being the causes of failure

Obvious from the appearance that this bike has a complete lack of maintenance.
There is a huge stress riser in the abomination of setup made worse by nobody ever opening it up to inspect, clean and regrease it.
Any reasonable bike mechanic would have spotted the problem long before it put you on the road.
It looks like the taper has indented the steerer, probably from being over tightened to stop the long dead headset bearings from knocking.
Completely preventable and a warning for others.

Lets not make any character judgements on the OP based on his bike wrenching / maintenance skills - some people are just not thinking about those things when they hop on the bike. Lesson learned, I guess. It also sounds like the mechanic who "fixed" the bike should be avoided in the future.


In any case this looks like an intersection of a bad set up / inadequate maintenance / strong rider flexing the front end.

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"They know f_ck-all over at Slowtwitch"
- Lionel Sanders

You've "never seen a bike with no spacers whatsoever under the stem" ??? You must not see many bikes. There's literally an entire website devoted to pictures of bikes exclusively with no spacers under the stem.

Also, an up-angled stem is common. It had nothing to do with OP's so-called "unusual setup."

Without being a dick about it, yea...I'd say most of the problem was a lack of routine maintenance.

I was always told 5mm spacer below if you can, but not necessary and always no less than 5mm left above this is necessary.

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2019 T-Rex Tri Series

When I went to a very reputable shop to have my steerer tube cut, I had to argue the 1 or 2cm excess with the mechanic. He wanted to cut it flush. Luckily, I had watched a GCN video on the process and didn’t give in. Honestly, I was really surprised he didn’t know that rule of thumb. All I know is that I left that shop with my fork cut at the absolute minimum of what I was comfortable with.

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Madison photographer Timothy Hughes | Instagram