How to avoid and anticipate breaking handlebars

Question

Recently while commuting my road bike (drop bar) handlebars split in half at the stem while I was riding. I took a spill but was luckily mostly unhurt. However, this was the second time this had happened to me (the first was ~5 years ago, on a different bike) leaving me to wonder how I can avoid or anticipate something like this happening again in the future.

This bike had last been tuned up about a year ago, but I don't know if any level of maintenance would catch weakened handlebars like this. I live in an urban area in the US with enough bike infrastructure to get around relatively comfortably but not enough to avoid potholes, curbs and other bumps entirely.

Are there any visual or structural indicators that I can use to check for weakened handlebars in the future? Or is it just the case that if I'm biking regularly in an urban area I should plan on replacing my handlebars every couple years or so?

Edit: On suggestion I've attached an image of the handlebars after the accident. Unfortunately I couldn't find any of them intact.

Answer 1

This is a reasonable question, but unfortunately a precise inspection and maintenance schedule isn't something that can be provided for bicycles. Additionally, cycling doesn’t have the infrastructure to do non-destructive inspections with things like ultrasound - apart from carbon fiber repair shops, if these are carbon handlebars. Aviation does this, but aircraft are many times faster and heavier than bicycles, and they often carry many passengers or valuable cargo, so the consequences of failure are much more dire - hence, they work this stuff out.

One first principle is to never exceed the recommended handlebar torque. For example, I think that Ritchey (just as an example) specifies no more than 5 Nm. This isn't that much torque, and it is easy to exceed if you're going without a torque wrench. However, if it's a cheaper part, there may not be a recommended torque - although it's also likely to be heavier, and thus less likely to break (barring manufacturing defects). 5 Nm is probably a decent starting place if there is no torque spec. If the handlebar slips when you try to press it down, you could incrementally raise the torque, say to 6 Nm, and re-test. Same principle with the shifter clamps.*

You can periodically take the handlebar out and inspect it for any visible damage. When you are changing cables plus bar tape would be a convenient time. That said, not all damage is visible, and this is not only true of carbon fiber. You can also try to monitor for any changes in how the bar feels, e.g. is there new creaking when you are riding, especially out of the saddle. This does require some awareness of how your bicycle behaves and sounds, however.

Additionally, if you crash, or even if your bike just falls over at a coffee shop, you should increase your vigilance, at least a bit. Falls like this are known to be able to damage carbon fiber components, and to cause failure later on. I would do the same if you had lightweight aluminum bars. For heavier bars, you can probably be less vigilant.

I don't know if many cyclists replace their handlebars regularly. I see that on some MTB forums, some posters say they pre-emptively replace their handlebars every few (e.g. 3) years. However, the bike is under more stress in this scenario. In any case, if your stem wasn't torqued too tight, it's probable that manufacturing error was the cause of your bars failing.

Note: I have a vintage-style single-bolt steel stem. It's custom, and it didn't come with a torque spec, and neither did my handlebars. My handlebar will slip at 5 Nm. I think I have it around 7-8 Nm. Stems with 2 or 4 bolts should require less torque.

Answer 2

I had exactly this happen to me a few years ago on my commuter bike. Due to road work bike traffic was diverted up onto the pavement, and as I returned to the roadway (off a slope, mind, not dropping straight off the kerb) the left half of the handlebar came off in my hand. Since I was turning and adjusting my balance at the time I lost control and fell off. (Fortunately there were no vehicles immediately following, so I just collected some bruises.)

I walked the bike directly to the shop. They said it was almost definitely metal fatigue (Al bars) and short of removing the bars would have been very difficult to spot. The stem clamp (on this bike) rounded in slightly, so the contact point, where it cracked, was actually slightly underneath the outside edge of the clamp. Even if I had checked visually I probably wouldn't have been able to spot it without removing the clamp.

The bolts weren't over-torqued, or at least not by enough to make a difference. I'd been riding the bike daily to commute for about 5 years, plus some touring and training rides for years before that and it probably had about 50Mm on it.

The mechanic at the shop wasn't sure if it was abuse from potholes on crappy roads, or I'd simply reached the reasonable lifespan of the bars.

Answer 3

I've never seen this sort of failure from plain usage.

Crash damage can weaken metal parts, especially if it gets bent back into line. Aluminium parts generally don't survive unbending at all.

My comment asking about the GMC Denali is that they have split bars from new, to allow cheap revoshifters to be installed without going around the hooks. So they have a literal spreader in the middle, around which the stem clamps. Sketchy.

I've got decades-old bars that have no such damage, both flat and drop. I've never heard of anyone I know suffering bar breakage. Clearly your situation is highly unusual - once is rare, TWICE is like winning the lottery.

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As for detecting such imminent damage, you can add this to your periodic inspections and visually look for a forming crack. The photo suggests it was outside the clamp and therefore visible, not obscured by the clamp.

Otherwise go on feel - if the handlebars feel softer, its because there's less metal holding them together. There is going to be a short period where the crack is propagating, but hasn't gone through yet and that may be noticeable. If it feels soft, stop immediately and inspect with a push/pull. Better to brake off while stopped!

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For you to experience some leeriness about the third time, is totally reasonable and understandable. Some possible ideas to help

• Choose some thicker-walled bars
• Consider fitting silvered bars rather than black bars - this may help show any crack. Then again the silver alloy should have been more clearly visible against the black coating. Try a push/pull while inspecting.
• Spend money and go for carbon fibre bars. Not cheap ones, go for a brand name with a decent warranty.
• Search out the kind of bars that have two strutts. This is for piece-of-mind - something like the Canyon hoverbar as fitted to their Grail gravel bikes.

I think this is ugly, but I haven't had the two experiences you've suffered.

Answer 4

After having several(!) steel(!) handlebars fail on me this way, I've taken to simply replace them every 10000km. Of course, this is always a compromise between risk of sudden, dangerous, unmitigatable failure and cost of regularly swapping handlebars. And things like the kind of roads you ride on and the way you ride are also part of the equation. However, overall the bars are not exactly the most expensive part of a bike, so swapping them regularly is not such a big deal financially.

Answer 5

Are there any visual or structural indicators that I can use to check for weakened handlebars in the future?

With aluminum alloy bars, I guess you could unwrap the bar tape every month, and remove the handlebar from the stem, and carefully inspect it for cracks. With carbon fiber bars, unfortunately, I'm not aware of any method that you can do at home, but then again carbon fiber doesn't suffer from fatigue, rather from damage from e.g. crashing, which could subsequently weaken it and cause it to fail "just riding along". So carbon fiber bar should ideally be replaced after every crash.

However, rewrapping the bars every month and removing it from stem isn't something you likely want to do. Thus, my advice would be not inspection but prevention.

You can reduce handlebar damage by following this checklist:

1. Your stem should be so-called "gapless" stem, i.e. at attachment point top it doesn't have a gap, all the gap is at bottom. The top is the most weak point on handlebars because it's under tensile stress (the bottom is under compressive stress). I believe with stems it's far more important to be gapless than to be polished shiny, so if you can only find black anodized gapless stems and polished shiny non-gapless stems, buy the gapless one, since stems rarely fail but handlebars fail often. (The best obviously would be a polished shiny gapless stem, but I'm sure you won't find one.)
2. If you buy aluminum alloy handlebars, never buy ones with anodized rough surface (which is usually black). The surface should be polished shiny, at least in the middle where the stem attaches (it's the weakest point). It may be acceptable to have a rough surface below the bar tape, because it may help the bar tape not to slip. Anodizing reduces fatigue life markedly.
3. Buy the heaviest handlebar you can find. Heavier is stronger. Ideally, that would be steel but unfortunately you can't find steel handlebars anymore.
4. Only buy handlebars with 31.8mm diameter in middle, because 25.4mm or 26.0mm is way too weak especially for aluminum alloy bars. However, with steel handlebars this doesn't apply, as the 25.4mm and 26.0mm attachments were originally designed for steel handlebars and then dangerously used for aluminum bars for a while.
5. Look at the level of technology used to manufacture the handlebars. In some cases, slightly lighterweight bar with better aluminum alloy or same alloy but with triple butting could be better, even though usually the rule of thumb is that heavier is better.
6. Carbon bars should be replaced after every crash that could damage the handlebars
7. If you use aluminum alloy handlebars, you might want to replace them every few years just to be on the safe side, since aluminum alloy has a very short fatigue life
8. Your riding style affects handlebar life. If you use your arms as suspension when encountering bumps, handlebar lifetime is increased.
9. Your choice of tires and tire pressure affects handlebar life. With as wide tires as possible, at reasonably low pressures, handlebar life is increased. Unfortunately many road bikes don't take wider tires than 23mm, but today this seems to be improving fortunately with disc brakes and 32mm may be easy to fit.