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Is there a point at which aluminum drop bars and stem are simple "too old" and need to be replaced?

Back story: I'm ever-so-slowly rebuilding a used (but new to me) 2006 Trek 520. I've taken it completely apart, down to the frame, had it re-painted and changed out most of the components. It's essentially a completely different bike at this point. Since it's been forever since I rode this bike prior to taking it apart, I don't really recall how well this stem/handlebar combo works for me. So I figured I would run the old ones until I get a better idea of what I want. But, after reading some horror stories online about handlebars/stems snapping, I'm worried that it may be a safety risk with something this old.

The handlebars are Bontrager Select 26.0mm diameter and 44cm length, if that matters. There's no visible damage, just a tiny nick at one end and faded paint. I have no idea what kind of falls any previous owner(s) may have been involved in.

Thanks

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2 Answers 2

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In theory, aluminum has a finite fatigue life, which is what drove the OP to ask the question. In practice, we might also want to consider the wall thickness: lower end bars and stems are going to have thicker walls and be heavier. Barring manufacturing error, you would expect them to be more long lived than lightweight aluminum bars. The expected lifespan might be quite some time for a casual rider.

One thing to consider is the practice of watchful waiting. Install the bars but try torquing them in the stand. Observe how they feel. Monitor for any noise or movement - I believe there shouldn’t be any in the stand. Under a full sprint you might expect a bit of flex, especially if you’re a larger rider.

If you do go about replacing the stem, then I know there are actually a handful of steel stems out there. Many but not all replacement stems will be for 31.8mm bars, as 26.0 is an older standard. This does mean that the existing 26.0mm handlebars will be lower end and thus heavier.

Failures in a lot of complex systems are gradual and then sudden. I think the precept applies to both carbon and aluminum stems and bars, with the caveat that the conventional wisdom is that you may not be able to detect an incident failure even with watchful waiting.

Personally, I am currently electing to run a 10 year old heavier aluminum handlebar. Some years have seen heavy use, some not so heavy. For what it’s worth, there have been no major crashes. That said, the stem involved is steel.

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    My current wet-day bike has the same set of aluminium drop bars I rode in the late 1980's. When I change the bar tape, I give it a good clean and inspection. If there was any cause for concern, I'd stop and reevaluate. So far, its been fine.
    – Criggie
    Jan 8 at 21:01
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    @Criggie But you've owned those bars the entire time, right? Would you trust them if they had been owned by X amount of unknown people prior to yourself?
    – Dan
    Jan 8 at 21:07
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    @Dan fair point. If my initial inspection didn't show anything of concern I'd ride it. Bends, significant scratches/abrasiions, cracks, or any "weak" or "soft" feeling parts would change that. These bars were used when I got them, but only by family.
    – Criggie
    Jan 8 at 22:10
  • How much value is really in knowing the history? How much damage can you do to a stem and handlebar without it being visible under close inspection with the naked eye? I’d love to see what a stem+handlebar looks and feels like after e.g. 90% of its maximum fatigue cycles under a certain load. Would the difference be obvious compared to a completely new one?
    – Michael
    Jan 9 at 12:47
  • @Michael The difference would be invisible. It's reasonably safe to say that a crack appears at about 99% of its fatigue life or so, and at 100% of fatigue life you will hurt yourself due to a failed handlebar. If there was a way to estimate fatigue life by looking at aluminum parts, the aviation industry would already be using the way. Now they just stop using anything that's dangerously close to the limit (which usually has been theoretically calculated).
    – juhist
    Jan 9 at 17:53
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Is there a point at which aluminum drop bars and stem are simple "too old" and need to be replaced?

Yes.

Aluminum has a limited fatigue life. The lower the tensile strength of the aluminum and the thinner the tube walls are, the shorter the fatigue life is.

However, it's not years ridden that matter. It's not even kilometers ridden. It's kilometers ridden hard. So if the handlebar has been used for leisurely countryside cruising on good-quality roads with wide low-pressure tires, it has never seen even one kilometer ridden hard. But if you ride it in roads full of potholes, or in city with lots of curbs, or with narrow high-pressure tires, you can easily accumulate kilometers ridden hard.

Unfortunately, it's impossible to say when a handlebar fails. The reason being that it could very well be that 220 gram handlebar lasts for 10000 km in some usage, and 300 gram handlebar lasts essentially forever (which isn't really forever since aluminum has a finite fatigue life, so it would be something like several million kilometers). How does 280 gram handlebar last then? Very hard to say, something between 10000 km and forever.

What I would do is to:

  • Throw away the old handlebar, since the history is unknown
  • Buy the best new handlebar you can find. Features to look for: butted tubing, 31.8mm stem clamp area (since that's the area where handlebars are most likely to fail), polished smooth aluminum surface at least near the stem clamp area as opposed to black anodized since anodizing reduces fatigue life, high weight, good-quality aluminum alloy, not any kind of stupid holes for Di2. For me, this is old Ritchey Classic that is unavailable now since they ruined it by Di2 holes.

Note that any kind of inspection doesn't tell if it's likely to fail. When a crack appears, it grows very fast. So to prevent fatigue failure by inspection, you would need to inspect it more often than every 1000 km. This would mean stripping the bar tape and removing it from the stem clamp area, although it's possible to "approximate" by looking only at the stem clamp area which is the area most likely to fail at least on the old smaller-than-31.8mm clamp areas.

While at it, buy yourself a 31.8mm gapless stem and ensure you install it correctly by eliminating the gap at the top so all of the gap is at the bottom. Gapless stems reduce fatigue failures of handlebars at the most vulnerable point. Fatigue happens as a result of tensile stress, not compressive stress, and the most vulnerable top clamp point is where the stress is tensile. A gapless stem eliminates stress concentrations there, making fatigue failure less likely.

As for stems, they are unlikely to fail due to fatigue since stems generally have more wall thickness than handlebars. However, stem technology has evolved and 31.8mm gapless stem has features you won't find on 15-year old stem, so replacement is advisable due to improved technology, not due to age. Also of course you will find stupidly-lightweight stems, since if some component is durable, it's obviously an opportunity for reducing weight, and for such ridiculous stems, what I said doesn't apply, they can and do fail.

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  • I do like the look of the Ritchey classic bar. Are you saying it's no good anymore because of the Di2 holes? Also, can you recommend a gapless stem with a big positive rise (+20 or more)?
    – Dan
    Jan 8 at 20:02
  • Well for someone not wanting Di2, the hole just weakens the handlebar without any useful purpose. Pro LT stem is available at 17 degree rise and my 7 degree rise version is gapless so I suppose the 17 degree rise is too. Edit: Oh, and now I found Pro LT at 35 degree rise too so all rise options available.
    – juhist
    Jan 9 at 17:48

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