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Several general questions have been asked regarding how long a bike or bike frame will "last", and the gist of answers seems to be that a bike can last quite a while if the replaceable components are replaced and the bike is reasonably well maintained.

But what about the inherent structural integrity of the frame itself? Is there such a thing as a risk of sudden frame failure or disintegration after some level of use? Do bikes ever fall apart, or develop a risk of breaking or fracturing along weak points? One of my bikes has more miles on it than the car I'm turning in — and I wonder about the integrity of the car!

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  • On one of those other questions I said a bike could last forever if you replaced things as necessary-- I was including the frame itself as a replaceable component! Yes they can last a long time but failures after around 50,000km or so due to fatigue are not uncommon even with steel frames. – user68014 Dec 24 '19 at 8:53

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Yes, frames do fail even if they're not crashed or ridden excessively harshly. The only way to mitigate this problem is to inspect the frame regularly during your maintenance and cleaning. Look for cracks. When riding, pay attention to creaks and squeeks and always find the root cause (it could be a crack).

Keep in mind that:

  • A bad weld could hold fine for years before coming apart.

  • Unchecked rust can eat through steel tubes, either from the outside-in or the inside-out. Once it starts, you have to keep on top of it or it will eventually take the frame. Rust also seems to have "good taste" in tubing by preferring the pretty Italian stuff to, say, gas-pipe schwinn.

  • Metal fatigue can form cracks that grow slowly until the frame suddenly snaps (I've seen this personally where the chainstay meets the dropout, and on crank arms).

Aluminum is the worst culprit for fatigue cracks. Aluminum seatposts and steerer tubes also have a tendency to develop aluminum oxide blooms that may permanently jam the seatube/steerer-tube in the frame.

Carbon typically won't survive a bad-enough crash. I've heard of long-term delamination issues, but never saw one personally. AFAIK every carbon frame "dies" in a crash or mishap that damages the frame to the point where the owner no longer trusts it. Anyone have stories about what happens to carbon that is not crashed?

For a concrete example, below is my own failure from a few years ago. It happened as I was cresting a very steep hill. I heard a loud "pop" and didn't realize what happened until I looked around and saw the chainstay separate from the dropout with each pedal stroke. This is a steel bike and was totally repairable, BTW. I didn't crash as a result (but neither was I going fast). Note the little bit of rust visible at the top of the crack. It indicates that the crack had been there for some time before the total failure. enter image description here

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    In the case of cracks or rust, there usually is a sign something is going wrong. Cracks take time to grow-- months or years, before catastrophic failure. The problem is that you might not know a crack is there until it causes a failure. They're hard to see. That's why it is a good idea to inspect the frame and root-cause each creaking sound. AFAIK, there is no MTBF (mean time between failure) for a bike frame. It would depend on too many factors (loading, random material imperfections, etc) and it would be statistical and thus not really useful for making individual decisions. – Angelo Oct 4 '11 at 20:03
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    That's pretty much what I was looking for (not that I thought to ask it that way): whether there were MTBF stats. But it sounds like, overall, it's not even enough of an issue that it's even discussed much. Certainly, it seems there's nothing like a recommendation to "discard after X miles", which one would expect if the issue were real (assuming the industry is properly regulated)—it's just hard to believe that something can be that durable (I change my phone every six months)! – orome Oct 4 '11 at 20:14
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    I haven't yet seen a CF delamination on a bike, but have seen it on cars and airplanes, so it's definitely something that can happen. – Brian Knoblauch Oct 5 '11 at 17:59
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    Also your point about carbon I feel is little too general, most of the DH frame manufacturers are now moving to carbon for the strength it gives. They're made in such a way that the frames don't weigh much less, but are much stronger than an equivalent weight of Al due to the fact that the properties are tunable by the way the laminates are assembled. – cmannett85 Oct 6 '11 at 10:47
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    @cbamber85, you're absolutely right. Carbon is fantastic and in usage dominates all competition bike frames for good reasons. It does what it is designed to do very well, but crashes put forces on parts of the frame in a way that no design can accommodate. – Angelo Oct 6 '11 at 16:37
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What you are referring to is sometimes known as catastrophic failure, when a frame fails under load. While this does happen from time to time, it's relatively rare. There are tales of defective carbon frames failing spontaneously while riding, but these seem to always be friend-of-a-friend stories. Most frames that do "fail" do so because of traffic accidents or other damage. And, as Gary points out, the bottom bracket (and mounting eyelets) are likely areas to wear.

Frame material also plays a part in this. Conventional wisdom in cycling circles is that steel is the most durable - it can be bent back into shape and even re-welded. Aluminum frames can't. And carbon fiber frames have a reputation for being delicate; if one of those breaks, you throw it out and get a new one, since any fixes will be unreliable.

While there is some truth to this, steel can be damaged to the point where it would be unsafe to fix and re-use. And carbon fiber is more durable than folks assume. But evaluating a damaged frame is often more trouble than simply replacing it. There are pro wrenchers who can do this kind of evaluation based on experience, but without putting the frame through an x-ray machine can you really, definitively say that a frame is safe to put your weight on after it's been bent and re-welded?

In general, yes, the frame is the most durable part of the bike. But it, too can be damaged beyond repair.

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    Just a note on the failure of carbon frames... My friend / team-mate broke his carbon framed mtn bike clean in half during a race. We were wondering why his lap was taking so long, when here he comes jogging out of the woods with his bike over his shoulders. Broken in 1/2, the 2 sides just held together by the cables. The manufacturer gave him a replacement frame in the end, but it does happen! – rally25rs Oct 4 '11 at 19:13
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    Another note on carbon frame failure: bustedcarbon.com – alxndr Jul 18 '13 at 16:23
  • Actually carbon is very repairable and unlike steel the repaired section is stronger after the repair than it was before the repair. It kills me when I see idiots in shops tossing out perfectly repairable carbon frames. Of course these are usually the same people who tell customers that aluminum is stiffer than steel when the opposite is actually true. – ChrisL Jul 13 '15 at 19:20
  • Tales of defective carbon frames are not alway "friend of a friend stories". There was a cases recently of a deadly crash when a carbon fork disintegrated (admittedly whether you see the fork as part of the frame is debatable, but it's a similar problem), see road.cc/content/news/… – Stephan Matthiesen Sep 19 '16 at 17:17
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Yes - frames are subject to wear, tear, aging and fatigue. The primary area of concern or failure on most frames is at the bottom bracket. On both metal and carbon frames this is a point of high stress and flex. But any weld or joint is subject to stress and may fail over time.

You should periodically inspect the whole frame, paying particular attention to and weld-points or joints. Look closely for signs of paint or weld cracking as well as any rust on steel frames. The best way to do this is to hand wash the frame and inspect it as you go. If you want it to last even longer apply a layer of bike or car wax your frame every six months or so. Wax makes it harder for dirt and mud to stick to your frame, and will make the next clean easier.

That said, if you make it a habit to clean and inspect your frame, are an 'average' rider (not excessively heavy or riding aggressively off jumps and drops), store the bike properly and care for it well it could conceivable outlive you.

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I have seen a few old steel frames that failed. In one case the down tube cracked in two at the point where the down-tube-mounted shifters were attached. In another case the crack was at the junction between down tube and bottom bracket. I've also seen seat stays separated at the seat tube.

But all of these failures occurred on bikes that had quite obviously been left out in the rain for years (if not decades), and all of them were still being ridden, even with the broken frame. The traditional steel "diamond" frame is extraordinarily robust.

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  • +1 for mentioning the robustness of diamond frames. Having cracked two frames myself (always downtube in my case), I never got why people would trust a Y frame: Any frame failure with such a geometry means rapid unscheduled dismount. A failed diamond, on the other hand, can usually be safely ridden to a stop after the failure happens. – cmaster - reinstate monica Dec 23 '19 at 7:48
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Just some notes on spotting cracks in metal frames:

Look for cracks in the the paint. These can be quite small even ~5mm long for instance.

Look at the stress points of the weld - that is usually just at the edge of the weld bead where the metal is most thin. Bottom brackets take the most stress of the bicycle but rarely fail because they are the most supported. Dropouts are most common areas of failure over time in my experience. Most crashes are from the front and will show up in the fork or where the head tube meets the down tube. Those are the spots to look.

Aluminium can snap suddenly. I've had this happen on handlebars. Usually steel will bend before it breaks and is much safer in that capacity. People who speak about carbon being durable are either fanboys or salespeople. Everyone knows carbon can break dramatically.

Front dropouts, fork crown and handlebars are really the ultimate safety check spots to watch. failures there can kill. Rear dropouts breaking will be bad but not super dangerous usually.

Fancy lightweight road bikes are the most susceptible. Frame failure on a steel commuter bike usually happens long after the bike has been junked for other reasons. If you are really worried about frame failure watch that front end, don't use aluminium or carbon and you will be fine riding even ancient bikes.

Sometimes slightly large or heavy individuals >200lbs will have more issues with frame fatigue than the rest of us as most bikes are designed for smaller riders.

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My Giant Explorer’s frame had a sudden catastrophic failure a couple of weeks ago. The duralumin frame split in two without warning across both tubes as I was dismounting, with the two wheels completely separating. It is a mere 9 years old, I bought it new, no-one else has ever ridden it, and it has not been mistreated in any way. Being a roadster type with a built-in carrier it should be designed to carry a load. It has had a fair amount of use, but only on roads and cycle tracks, and mainly for shopping, travel or pleasure. The tubes fractured at what is clearly a weak point, where the cables entered the tubes. This should be a warning to other owners of this model to check the frame in this area, especially the bottom tube. I was only relatively lightly injured, but it could have been far worse, even fatal, had I been in traffic or travelling at speed.

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  • In my opinion having cables enter the frame is always a weak point and a sign of poor design (except in the case of very high end bikes where there is a lot of material added inside - even then its going to be a stress point). I've seen cheap steel frames buckle at the insertion point several times. – rusl Mar 9 '16 at 5:54
  • FYI Giant warranties their frames for life. You should have got a new equivalent bike out of it for no cost, or had that retail cost subtracted from the cost of a higher-spec bike. – Criggie Apr 21 '17 at 5:23
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I managed to break a steel frame about 2 years after buying it. That did involve a crash a year after owning it and then riding it to destruction though. I noticed after the crash (into a ditch) that the geometry felt shorter and tighter. I just carried on riding it though. In hind sight that might not have been the most intelligent thing to do.

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  • That's a concern. I've ridding this thing for long enough, and treated it badly enough, that I wonder when and if it will just give up the ghost. – orome Oct 4 '11 at 20:43
  • As I say, there were some clear indications that the frame was damaged. The geometry changed, i.e. I could tell that the wheels were closer together afterwards. If I had closely inspected the frame I suspect I would have seen flaked paint and an indication of the damage too. On the day it finally did give up the ghost it felt funny, groaning and generally not feeling right too. I didn't come to any harm when it snapped in this instance although it was unrideable afterwards. Basically you have to ignore a lot of signs to actually let that happen. – Colin Newell Oct 5 '11 at 7:55
  • @2u2, my alluminum frame took about 10 days of commuting, all the time groaning and flexing, to break. A large crack was growing about 2-3 mm a day, until it went all the way around the upper tube. – Vorac Nov 22 '13 at 10:54
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I've seen three bicycles with what appear to be stress fractures at the bottom of the seat tube and top of the bottom bracket shell. A bike nut friend with more metallurgical knowledge than me tells me that this is caused by work hardening -- which is the same thing that causes a paper clip to become brittle after repeated flexing. Now that this has happened to my trusty chrome-moly Fuji Gran Touer SE frame after 20+ years of daily use, I have a suspicion that the habit of mounting and dismounting on/off the left pedal while rolling is something that probably puts lots of extra stress/flex on this joint.

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    Work hardening is much more likely with aluminum than steel. You hardly ever see it in (properly engineered) steel. – Daniel R Hicks Jul 12 '15 at 13:33
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    I'd also note that the bottom bracket is the place in a standard steel frame which is most prone to internal rust. – Daniel R Hicks Jul 12 '15 at 14:00
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Let me attempt to go just slightly further than the other answers so far. My ability to explain this well may be limited by the fact that I'm not an engineer. I'd welcome any corrections.

Fatigue-related lifetimes

This section details frame life in relation to fatigue, i.e. after repeaated normal use without crashes or damage. Conventional wisdom is that steel and titanium are the most durable frame materials, e.g. [this answer] to a related question1. This requires some unpacking. Many materials experience fatigue after repeated loadings (e.g. pedal strokes). Let's just quote Wikipedia on this bit:

In materials science, fatigue is the weakening of a material caused by cyclic loading that results in progressive and localized structural damage and the growth of cracks. Once a crack has initiated, each loading cycle will grow the crack a small amount, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure.

Steel and titanium, however, have a fatigue limit. That is, any loading below a certain critical amount will not cause fatigue at all. I'm not sure what's the critical amount for each material, however, and I'm not sure what sorts of impacts would exceed it (e.g. I suspect many vehicular impacts exceed that limit for both metals). Aluminum (link to Lennard Zinn) does not have a fatigue limit. Any amount of load will weaken the metal, and it will eventually fatigue and crack.

However, recall that they make airplanes out of aluminum, and planes can be in service for decades. So, depending on the quality of construction, we might expect aluminum frames to be able to have very long lifespans. Indeed, Sheldon Brown's site has a link to a 1997 test of 12 frames by Tour Magazine (translated from German by Damon Rinard). The test contained 4 aluminum frames (e.g. Cannondale CAAD 3), 4 steel frames (e.g. lugged De Rosa SLX, welded Fondriest), some carbon (e.g. Trek OCLV monocoque, Time Helix with carbon tubes in aluminum lugs), and some titanium (e.g. a Merlin Team Road).

These were all high-end frames, and they may have skewed towards light, thin tubing. However, one carbon and two aluminum frames (Trek OCLV, CAAD3, and Principia RSL) made it to the end of the test, while none of the selected steel frames did. So, aluminum may have a theoretical limit, but it may be difficult for amateur cyclists to exceed it in practice.

I am not sure what, specifically, I heard about carbon fiber and fatigue earlier on in my career. Carbon fiber may actually not be very susceptible to fatigue. In this Cyclingtips article, several bicycle composites engineers say that it does not fatigue in the sense discussed above. Carbon fiber frames may last your lifetime, barring damage. The aviation industry is increasingly moving to carbon parts, and again, they would not do so if carbon were fragile. Planes have to have a multi-decade service life because they are extremely expensive.

Manufacturing processes

Again, I'm not a materials engineer, but many of the frames in that 1997 test failed at joints, e.g. at lugs or at weld zones. For titanium, the welds must be done under an inert gas. If any oxygen or nitrogen gets into the weld, it can make the material there brittle, and that will crack. I am not sure what the chemical issues are for steel and aluminum, but I suspect contamination at the welds is also possible. Quoting Zinn again:

If you had a steel or titanium frame, I could make no such prediction of certain fatigue failure. That’s because, if the frame’s designer chooses steel or titanium tubes whose tensile strength and dimensions (wall thickness, diameter, and shape) are such that the stresses seen while riding will never exceed — say, 40 percent of its tensile strength in its heat-affected (i.e., weld) zones — then the frame will last indefinitely in the absence of a crash. Of course, notches or dents or poor welds (or, in the case of steel, rust) will lower that limit (as well as lower the tensile strength) and cause fatigue failure to occur at a lower stress or lower number of cycles.

Zinn also alludes to the heat affected zones in steel or titanium. I believe this means that due to the intense heat during welding, the frame is weaker at the zones affected by heat. I think this is one reason why silver brazing or lugs were a potential alternative to welded steel, as those processes are done at a lower temperature. However, the Tour test shows that lugged steel can also break at the joints. That might be due to contamination in the lugs. We obviously don't know precisely why the frames in the Tour test broke, but reading the table of failures on Brown's site, many of them seemed to be at joints. That makes me think those were failures of manufacturing processes.

To my knowledge, carbon frames are typically made out of pre-formed carbon sheets that are arranged in a mould. Then, resin is added, and they bake the frames. I believe that usually the front and rear triangles are made separately, then bonded together. Carbon frames may have different issues than heat treatment. Raoul Luescher has a Youtube channel where he cuts into crashed carbon frames that are sent to him for evaluation. He frequently finds voids (i.e. holes) in the carbon. He's an ex aeronautics engineer. He seems to indicate that these are issues, but I'm not sure I've seen a detailed explanation. I'd suspect that voids can act the same way as tiny cracks in metal frames, and that repeated loads could cause the void to propagate (i.e. expand) over time, and eventually lead to what we might perceive as a fatigue failure.

Also, carbon fiber is in fact made of many thin and very strong fibers. In one podcast regarding a recent group of carbon fork failures, he said that some forks were designed with fairly square corners in the steerer to help cables pass through the area. He reported that the sharp bends are very stressful for the carbon, and that this can be a point of failure later on. I recall (not able to find the link) to a Youtube video where he discussed handlebars with holes for internal cable routing (for electronic drivetrains), and he said those holes could be a point of failure if the carbon took loads as well. Basically, never mind manufacturing defects per se, some design choices might create points of failure that the bike company engineers weren't expecting in carbon fiber.

Damage

Back to the Zinn passage quoted, dents can be a starting failure point in steel or titanium frames despite their materials characteristics. Obviously, they'd have the same effect on aluminum frames. Many of us have the sense that carbon fiber is fragile, and that probably stems from its known lack of resistance to impact damage. So, you could damage your frame from even relatively small impacts. That might not cause an immediate failure, but it might eventually cause the frame to fail. Steel can rust as well. However, I believe carbon frames may also corrode from salt. Unpainted aluminum can as well.

TL;DR for consumers

Manufacturing process defects and damage are probably the biggest threats to your frame’s life. I would wager that all frames are possibly at risk from these issues.

Be especially careful handling any carbon frame, and any frame built of very light tubing. The conventional wisdom among the Internet forums I frequent is to be skeptical of any used carbon for this reason. Consumers might want to be skeptical of frames which are pushing the performance boundaries of the material involved, e.g. frames with ultralight tubing. Consumers might want to bias their selection towards manufacturers with lifetime warranties, although that does depend on the manufacturer surviving your lifetime, and on you maintaining sufficient records.

In theory, consumers might be able to avoid manufacturers with reputations for frame defects. The problem is, I’m not sure how you would practically assess this aside from gathering anecdotes.

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Years ago I had a steel frame (Trek 700) break at the seat stay and dropout. I think this may have been caused by flexing due to the fact that my rear axle had previously broken. The bike had been well used for at least ten years.

FWIW I also once broke a JIS crank spindle, maybe also due unusual forces from a loose crank fixing bolt.

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As student I used a step-through brazed steel frame which was >30 years old.

So, that bike had a particularly weak frame geometry. Its beginnings are unknown to me - my dad bought it used at some point. He then used it for recreational purposes, so not that much distance but forest paths plus some load (kid on back seat). At some point I inherited it as a bike sufficiently old that it could be left locked over night in a university town without too much danger of it getting stolen.

It failed in the sense that it started to twist with each pedal stroke when I pedaled hard (after about 5 years as my primary university bike). I suspect the lugs/brazing. Nothing sudden here, though.

I don't know how much longer it lasted, I gave it to someone who was looking for an old bike for occasional light use and who didn't care about the flexing as it wasn't wasn't yet that bad.

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