Had LBS re-cable my bike, went in to pick it up today and the mechanic pointed out that my Thompson Elite X2 stem had a pretty significant crack I hadn't noticed Probably saved me a huge dental bill or worse. The stem probably has 10,000 miles on it and is several years old on my beater bike. I was pretty surprised as the Thompson is known to be a pretty stout stem especially for it's weight. My bad, should have been inspecting my bike more often, hope everyone else will too. Just ordered an Easton EA90 to replace it with, hope it will do me a little better.

I assume its the faceplate that cracked? Its a known issue. Call Thomson and they will send you a new one. Note...... There is no "P" in Thomson

How was it cracked? Pictures?

Many times it cracks from overtightening.

You are very, very fortunate that nothing bad happened. And, so am I. I still shudder when I recall a time when a stem cracked on me while I was riding my bike at the start of this 1/2 mile 14% grade. I noticed the problem just in time. We all just need to inspect our equipment regularly. And hope for the best. In my case, I believe it was just a defective stem and not the result of over-torquing; but, as Timothy says, over-torquing is often the problem.

A fair assumption(it's a common failure), but inaccurate in the case of my cracked Thomson stem. Mine started to split at the 12 o'clock position looking down at the steerer tube top cap.

Did Thomson replace it?

Had a Ritchey WCS AL stem crack vertically starting from the steerer tube. Also had well north of 10k miles. Definitely some fatigue to watch out for in the lightweight stuff.

Samesies! However, due to wanton neglect. About 15k miles.


Like Wilford Brimely said, "check your stem, and check it often."

No they didn't, but it was way out of warranty.

Any way to see this with the stem installed?

Holy crap, this thread is scary.

if I hadn't been using a garmin mount that was connected to a steerer tube spacer, it would have been more noticeable. This X4 stem was on a SS hardtail mountain bike.

But it was Light while it lasted..

boring 'heavy' stuff may last longer..

Never been removed since installed by professional highly regarded bike mechanic using torque wrench. I have no clue how to get a pic on here from computer and don't have a smart phone.

Right, no P. Actually it cracked at 3:00 looking down on the headset, the section going around the steerer tube.

Guess you could let that one go till the crack reached the faceplate. Seriously, that is the strangest place for a crack to appear.

Yes, very fortunate the mechanic spotted it, must not be my time to go just yet. Thing is, I rarely get out of the saddle or sprint so I would't say I've ever put a lot of stress on the front end. More of a climber, love to sit and grind up the foothills of N.C.

Thomson stuff is very strong and heavily tested, and not much lighter than other production stuff out there. Popular in downhill mtb circuit, etc... Nothing gets by without a failure here or there. Let's not misinform the lurkers out there...

You know what fascinates me and strikes me as ironic about this incident as well as my own near-disaster is that these were both cases of metal alloy stems failing. I have always done tons of climbing and I'd have to say that I put considerable stress on my stems/bars because I'm often out of the saddle and moving the bike around to get up some pretty severe gradients. In my case, I was then riding a friend's old bike, but the stem was actually pretty new (it was a Cinelli quill stem; metal alloy).

I currently have two carbon fiber bikes and both have carbon fiber stems as well (and bars). I always look at them with suspicion when I ride, yet put my full trust in them. Or, better stated, I put potential problems out of my mind. Nothing has happened yet and hopefully nothing will.

Yes, my primary bike, a Cannonade Evo has carbon stem. I don't know but I would think that metal has a fatigue life whereas carbon does not. I would think that there would be more metal stem failures than with carbon but I could be wrong. Anyone know?

Please do not read this as some kind of critique or warning, but.....

Thomson, like many makers of "machined from billet" stems don't do a step that was common BITD of forged quill stems.

Ball burnishing "tightens" up the surface structure of aluminum parts, partly duplicating and/or enhancing the effects of near net forging. By compressing and flowing the surface it closes surface micro cracks that may otherwise become the seeds from which cracks grow.

As mentioned, ball burnishing used to be SOP, but has gone out of fashion, probably for cosmetic reasons. Also keep in mind, that aluminum, (both forged and machined) is vulnerable to corrosion, which cause surface defects that later start the cracking/fatigue process.

On the bright side well designed and built can tolerate crack formation for quite a while before failing. I suspect that this stem's crack woulf have become obvious either by sight or sound (creaking) or even by feeling looser well before it let go.

So, don't obsess, but don't neglect or take your aluminum parts for granted either.

Come to think of it, my FSA stem is aluminum covered in carbon. Wonder how I am supposed to see a crack forming in the metal if it's covered.

That makes sense to me. My crack is vertical across the whole band of metal. It is an obvious crack running the entire length but I don't think it has gone all the way through. I haven't taken the stem off yet as I'm just waiting for the new stem to come in the mail before I swap them out.

Heh - with all the cheap carbon imitation stuff being bought online right now, still the only bar/stem I've seen catastrophically fail in person was a Ritchey aluminum bar during a downtown crit. This was about 10 years ago btw, and I was later told it was due to some kind of corrosion that happens with aluminum on aluminum parts & sweat (I think). And that it has to be neglected for a while. Somebody here might know more about that type of corrosion. The guy did crash hard and break a collar bone.

It stuck with me enough that I started checking my gear, and I actually replaced a couple of bars/stems 'just cause' after a couple of years of use.