I keep reading that aluminium has no fatigue limit and that bicycle frames made from it will fail within quite short periods of time. Is this true or just a myth. I donīt seem to remember reading any posts where someone with a decent aluminium frame has actually reported a real-life case of frame failure due to metal fatigue.

Can anyone out there report real life cases of aluminium frame failures caused by metal fatigue. I donīt mean resulting from crash damage or botched welds. If so what were the circumstances - age of the bike etc.

I have a couple of aluminium frame bikes and it would be nice to have some evidence that frame replacement is necessary before I junk the frames in a couple of years.

I'm sure it's probably happened but I'm equally sure it's happened with other frame materials too. To be honest, despite the fact that I'm not a big fan of Al frames, I have yet to see one fail during the normal life of a frame. The only times I've actually seen an Al frame fail was on MTBs that have been subjected to jumps and hucking.

BTW, here's a pretty good webpage that compares various metals used in bike frames.

I have a Trek 7000 frame that's like 9 or 10 years old. I've ridden it hard the last 6 months or so, (knock on wood) so far it's a very strong frame. No complaints.

My Klein Quantum frame's hanger snapped, NOT from a crash, but my guess is fatigue. It was about 5 years old when it happened, so I'm not surprised.

I've never had a bike frame that didn't last longer than I wanted it to. I always develope a yen for something new long before the old one gives out. I kind of think that feeling is the real basis for the aluminum fatigue limit stories because, years ago, I used to hear similar tales of steel frames losing their rigidity after a couple of years.

Very few fail,most dont so i would worry about other things. Also a difference in frame life from racing to just riding.

I have seen quite a few frame failures. Some just from age/wear, some from crashing. The only spectacular failures I have seen were on two alluminum frames, A Giant, and a Cannondale. They both snapped off the headtube. I also caught on video tape a Ti frame snapping a headtube of during a race. There have been lots of mundane failures, just a crack propogating. Just this past friday I took a steel Performance bike out on a test ride and when I went off the curb the down tube snapped in two. To be honest I would not have noticed it(It just made it a little more springy and it had a cheap fork) except it suddenly shifted front and back when the frame spread.

So I would say, get what you like,treat it like you want, and don't worry about it to much. Worrying about a frame break, is like worring about getting struck by lightening. Just check the frame over every now and then.

I've been riding aluminum since 1987 and the only frame failure I had was an older trek frame that used the bonding of tubes with some kind of glue at the bottom bracket and head tube.

The bond on the bottom bracket came apart during a downhill run.

All welded aluminum frames I've owned have been bullet proof, especially the Cannondales. And I've ridden C'dales for the past tem years except one Specialized Epic I now own.

Its true that Al is about 1/3 the strength of steel. It is also about 1/3 the density. Bike designers use more volume of Al, using thicker-walleed tubing. They also use fatter diameter tubing to build a stiff structure. Al will fail if you keep bending it, so stiff structures are used to prevent fatigue.
In practice a good Al frame will last as well as any good frame. Most failures are due to faults in manufacturing, leaving stress-raisers which concentrate stress, or giving heat-treatment during welding/brazing.
The one big weakness of Al is at the derailleur hanger. These do get mangled up more easily than steel, and cannot be bent back in shape. Even replaceable hangers have their drawbacks; the attatchent point can get bent, and you have to buy the replacement part many years after buying the frame. Will you find one that fits?

According to Grant Petersen of Rivendell, a major manufacturer recently had to recall some aluminum bikes because of 2 frame failures. One buckled while a customer was test riding and the other buckled while a customer was doing a track stand on the shop floor.

I don't know which company but my guess is probably Cannondale or Specialized. Both companies, especially C-dale, like to push the limits of Aluminum.

I believe it's more internet myth than anything. The percentage is so low that there's a lot of repetetive "I know a guy who.." goes on.

the concern about Al-alloyed frames arises from that it has lower tensile strength and also lower yield strength than Fe-C-based alloys. Al alloys are more prone to breaking without yielding than are Fe-C alloys. theoretically, if you ride hard enough, the frame will fail, though i have never known anybody whose Al frame has failed from normal use.

Myth,folklore,BS:WHATEVER!! Engineers, and metalurgists know how aluminum fails and design around it. Several 'lifetimes' worth, whatever constitutes a lifetime.

I had a friends brothers cousins girfriend that worked with a guy that knew somebody whos dog saw bigfoot once.

OK. They obviously are not exploding under riders on a regular basis. If YOUR frame failed, post up. Let's see how many there really are. Frames of any material can fail due to a myriad of reasons. Most are probably due to reasons other than material fatigue. My 7 year old Al GT MTB is holding up just fine. I have been in the air more than a few times at over, I'm ashamed to say, 200 lbs and it is fine.

This obviously was not a fatigue issue. Sounds like bad welds - really bad welds. This is a workmanship problem, not a metallurgical one.

Al has a limited number of fatigue cycles it can go through, afterwhich the frame can fail. That said the number of cycles is high enough that its very rare for a normal rider to do so. On the other hand, I've heard that racers should replace their frames after 10,000 miles

No myth, it's only a myth to those who own aluminum bikes because they don't want to think about it; kind of like saying your Hyundai is going to break more often than my Lexus...I have insulted your buying decision now your upset. It's common knowledge that AL always has some threshold in fatigue cycles beyond which it will fail. First you have folks right here on this post saying they had failures. There have been many post over the past year on the bicycle.com forum of failures. I have a friend who back in 1986 bought a Vitus AL and it failed about 7 months after buying so his LBS allowed him to move up into a Klien stating that due to his 245lb weight he stressed out the smaller tube Vitus. Over the next 12 years he broke 3 of the Kliens; then someone said Cannondale was better so he bought one and 9 months went by and it broke but it took 8 months to get Cannondale to replace it so he bought a steel Gios in 1999 to ride in while waiting. He got the Cannondale back and less then a year later it broke except this time he threw in the dump! He still rides the Gios today and so far no problems. But he likes steel so much better that he bought a Rivendell for touring last year.

By the way, glue bonded lugged AL frames are actually stronger than welded tubes. The reason the glue bonded lugged frames of days gone past failed was due to the use of the smaller diameter tubing which flexed to much causing the glue to eventially fail-which on welded tubes of the same diameter the failure rate was more than 4 times as much! The reason they stayed with the welded tube was cost.

see for more info: https://www.exploratorium.edu/cycling/frames1.html

Also a book by: Hayduk, Douglas. Bicycle Metallurgy for the Cyclist. Says this about AL frames: "Aluminum is light and cheap and always large-diameter because, like a presto log or a block of pink popcorn, it doesn’t stand up to repeated flexing. Aluminum has a short fatigue life, so the smarter makers eliminate fatigue-inducing flex by using huge diameter tubes. There are some fine aluminum frames out there—notably, the ones made by Charlie Cunningham and Gary Klein. They at least, have some flesh and blood and brains behind them. But today’s cheap-labor imitations have nothing to offer beyond their function, and if you can warm up to one of them, you can likely warm up to anything. Consider yourself lucky?"

VeloNews last summer (on page 42) had a product guide issued and made some disparging comments about AL framed bikes: "VeloNews dated 6/10/03, page 42. “As anyone familiar with beer cans can tell you, al is softer and less stiff than steel. Al is easy to draw and form into shapes, easy to machine and relatively easy to weld. Its density is about a third of steel and half of ti, so it is not hard to build a light bike with it. It will oxidize, and should be painted, powdered coated or anodized to prevent corrosion, but it does not rust away rapidly. Al has downsides too. Its tensile strength, yield strength and elongation are far less than those of high strength steel and ti alloys. Al is more vulnerable in a crash. Al has no fatigue limit, a property steel possesses, often expressed as a % of its tensile strength. Below this limit, the material can be cycled indefinitely without breaking. This means that al can be less predictable than steel as to when it will fail after long use. Back to our beer can: compare a can of beer to a metal can of olives and it’s apparent that he al container has much less stiffness than a steel can of similar thickness and diameter. Yet many al bikes feel stiff. Why? It’s because al’s density is so low; tubes can be made large and thick for stiffness and light weight. Al can be alloyed with other elements to enhance its properties. Scandium for instance is an element that can help make a very strong al alloy."

I could go on but why?

This whole issue of AL being used to construct bike came about in the early 80's when cycle manufactures where losing money on bike frames because of all the hand work it took to build a bike. So they found that with AL they can have mass production robotic machines weld the tubes saving labor cost; PLUS they can use recycled AL and save on material cost. The average AL frame made in Asian plants cost $45 (a little bet less in China and little bit more in Thailand)...that includes labor and material! Why do you think Nike builds shoes in China? So they can get the shoe for $5 and sell it to you for $120, the reason: PROFIT! And all that profit does not have to pay for insurance or lawyers for workers here in the States. No wonder 90% of the crap in WalMart is now made in China.

And steel can't be welded robotically? So those cheap xmart steel bikes are all welded up by hand?

I'm just gald that airplanes are not made from that unpredictable aluminum stuff.

My two favorite bikes are AL. One, is ALTEC2 and after 4 years and about 10,000 kms is as stiff as the day I bought it. Ditto my Ishiwata tubing double butted CrMo commute bike with 15,000 kms in the same period.

But I only weigh 66 kgs. A friend who a big powerful sprinter turned his Pinarello Paris into a wet noodle in 3 years. You could see the whole frame flex just by pulling on the handlebars.

These are just datapoints. Take the info as you will...

Ive seen a few cracked and failed aluminium frames but the only ones I've personally broken or cracked have been made of steel..
True Temper's finest too boot..

I suspect aircraft may be built of a tad higher grade aluminium and hopefully tighter quality control, but they still crack and suffer fatigue problems as well.(hopefully not while I'm in one )

Yes, aircraft do suffer from fatigue. Yet, designers can still predict the performance of aluminum and build a safe aircraft.

All materials will fail,sooner or later.Wow,i'm pretty smart.

Yes and no. New materials are appearing all the time in the aerospace world but the materials used in bikes today are actually borne out of that world. Most high quality bicycles use aerospace grade versions of their respective material (steel, aluminum, carbon fiber, titanium). The quality control can of course vary but respective bike builders have as good a quality control as Boeing. Airframes do suffer cracks and fatigue of the course of their lifetime. Sometimes these can be repaired but there are plenty of aircraft that were placed in a "degraded status" with reduced mission responsibilities due to airframe age. One example of this was the C-141 which had its mission profile reduced when the majority of the fleet began showing cracks along the dorsal spine... yet the Air Force was still flying them. Careful inspection of your frame is essential to safety. Wash your bike, go over your frame and spot problems early. All the macho mountain bikers who brag about never washing their bikes are just being foolhardy.

Well, it is nice to know from the very first sentence that this writer does not know what he is talking about. AL less stiff than steel - not in this universe. Comparing a beer can to a steel can is crazy. The thickness is about ten times different.

Don't believe everything you read.

It is true that AL can only be cycled a certain amount of times. The magic here is, what constitutes a cycle? A properly designed frame will not be clicking off a cycle with every pedal stroke like people seem to think.