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I had this happen to me on a second hand bike that I did not know the history. The bars snapped at the stem, luckily I was just accelerating away from a junction and still at lowish speed, so was not injured. Since then I never ride on second hand bars.
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Heat treated will be safer (according to Nitto anyway), theirs come with a red band to indicate this.
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I would think it's more of a concern with a quill stem (rather than one with a removable faceplate): bars get "screwed" into tight clamps, scoring them.
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Apparently aluminium handlebars should be regarded in the same way as chains and tyres, needing to be monitored and replaced every N km?
Fundamentally, that applies to any aluminium alloy component. The material has a finite fatigue life. The edge of the bar clamp is the maximum load point on a bar, and even after allowing for the centre section being a larger diameter and, on good bars, thicker walled, it's likely to be the stress maximum, so that's probably going to be the point of failure.
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In the 1980s, 3T and Cinelli warned users explicitly that handlebars had a service life dependent on usage. I do not remember what those limits were — perhaps 25,000km? — but it was significantly lower when used in competition.
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are properly manufactured and installed handlebars really also that vulnerable?
Even relatively new ones are not completely immune to catastrophic failure if their short life has consisted of resisting a Ukrainian kilo rider's starting pulls 😀
https://www.youtube.com/watch?v=jp0AtxFWHWM
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Until only a couple of years ago the Brompton owners’ manual said this.
- ALUMINIUM COMPONENTS: as on other lightweight machines, aluminium alloy is used in the construction of the Brompton, and this material has a finite life before failure. In normal use, the risk of aluminium fatigue failure is remote, even after many thousands of miles. However, the risk of failure increases with use, especially with hard riding or other severe loading: as such a failure could cause injury, the hinge clamp plates, handlebar and chainset should for safety be replaced every 5,000 miles (more frequently on any machine subjected to hard use), and we recommend that these items are anyway checked regularly.
The current manual doesn’t seem to have a specific mileage number in it anymore.
I’ve not seen such a warning on any other bike part. As the bicycle technological clock at Brompton stopped in about 1982, I suspect it reflects received wisdom at that time.
- ALUMINIUM COMPONENTS: as on other lightweight machines, aluminium alloy is used in the construction of the Brompton, and this material has a finite life before failure. In normal use, the risk of aluminium fatigue failure is remote, even after many thousands of miles. However, the risk of failure increases with use, especially with hard riding or other severe loading: as such a failure could cause injury, the hinge clamp plates, handlebar and chainset should for safety be replaced every 5,000 miles (more frequently on any machine subjected to hard use), and we recommend that these items are anyway checked regularly.
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Surprising conversation with a shop manager today about handlebars breaking where they meet the stem. Apparently aluminium handlebars should be regarded in the same way as chains and tyres, needing to be monitored and replaced every N km? News to me. I know (old, steel) rock climbing carabiners can develop micro fissures and fail catastrophically, but are properly manufactured and installed handlebars really also that vulnerable?