How many years an aluminium frame lasts in a touring bike?

Question

How long does an aluminium frame lasts in a touring bike?

[Removed extra questions to be clear.]

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Background

So far I preferred aluminium vs. steel for many reasons, but if steel lasts significantly longer, for my next touring bike I will go for steel.

My Cannondale Badboy 2004 has a crack in the alu-frame. I was surprised by this, I thought my bike will last 20+ years easily. The workshop they said this is a high quality, strong frame, but after 10 years alu frames can get tired. Especially if I use my bike both in winter and summer, as the heat change wear alu faster. They say it can be welded, which will cost significantly less vs. a new frame (if it is available), but I should be prepared for other cracks to appear. The workshop contracts a welder specialized in bike frame welding and repair.

I also found a scientific research article on this topic. If someone has access to ScienceDirect (Cicero et al. (2011): Analysis of the cracking causes in an aluminium alloy bike frame), I'd be interested in the conclusions.

I'm interested in touring bikes, not road bikes, city bikes, etc.

I'm happy to update/clarify my question if needed, make a comment.

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Topics I have researched:

2. Maintenance on an Aluminium frame
3. Which type of frame is better for a touring bike, steel or aluminium?
4. Is it possible to repair a dent on an aluminium frame?
5. What are the pros and cons between an aluminium and carbon frame?
6. Is torque relevant for steel/aluminium? Where do I find torque specs?
7. non-steel frames and longevity
8. http://forums.mtbr.com/frame-building/aluminum-welding-cracked-frame-134600.html
9. http://singletrackworld.com/forum/topic/repairing-a-cracked-frame

Crack in the alu frame near the rear axe (the bike is upside down):

Answer 1

There are a lot of question so I will settle on the one in the title.

How many years will an current aluminum frame last of a touring bike?

Depends:

• Don't know what aluminum frame
  Construction is a larger factor than material
• Don't know the use
  Use is a larger factor than material
• Don't know how you are going to care for the bike
  Care/maintenance is larger factor than material

Aluminum has not changed in the 10 years

All we know is your last aluminum, high quality, strong frame bike lasted about 10 years

The best guess is your next aluminum, high quality, strong frame will also last 10 years
Really that is the best guess

That is as vague as how long will a current pair of sneakers last me?
And the best guess for how long my next pair of sneakers will last is how long did my last pair last.

Aluminum fatigues and steel does not fatigue. As stated in a comment steel does fatigue - well not always. Mild steel will not normally admit fatigue crack growth if the applied stresses are below about 10% of the strength of the material. Materials, such as aluminium alloys, do not have any such fatigue limit. If a cyclic load is applied, aluminium alloys will always fatigue. For the same strength a steel bike is typically going to be heavier than aluminum. But you get a bike that is much much less susceptible to fatigue. With steel you also get a bike that will take a ding (dent) and not compromise structural strength to the extent of aluminum. Not exactly the same thing but at the molecular level they are related. Frame Materials

Found a quoted number. Just because it was on the Internet does not make it right but here is a 5-10 year quote.
Bike Frame: Aluminum Vs. Steel

Aluminum frames possess the shortest fatigue life of any material used to manufacture bicycle frames. The typical aluminum frame possesses a life expectancy of five to 10 years. The fatigue life of steel is much longer, but the material requires more maintenance. To prevent rust formation steel frames must be cleaned and polished regularly and periodically coated with rust stop on the interior of the frame.

If you are discounting steel because it will rust then you are not caring for the bike properly. A properly maintained and stored steel bike should not rust. And for sure it should not rust out in your life time. You stated bikes from you fathers era lasted 40-50 years - pretty sure they were steel bikes.

If you want fatigue free and rust free then get titanium.

Answer 2

I researched more on this topic.

The short answer is that an aluminium frame can last from a couple of years to 50 years/lifetime.

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The long answer is:

• The main factor is fatigue (not counting accidents): "The tendency of a material (metal) to break under repeated cyclic loading at a stress considerably less then the tensile strength in a static test."
• The sign of the end of life of an alu structure is a fatigue crack, when the first crack appears, probably more will come. A few years can be gained by welding but it will fail probably at another place. Regular inspection is needed to avoid a total failure.

Main factors in aluminium frame fatigue:

1. Design, manufacturing, welding, material: determining factor for 90% of bike owners, as they don't use the bike that much that they would fatigue it with use. We, on this forum, are probably in the other 10%.
2. Environmental conditions: saline, humid, big temperature changes increase.
3. Use (rider weight, terrain): heavier riders fatigue more, and more use over time increases the chance to fail significantly. For heavy users, who buy good frames anyway, and take care of the bike, probably this is the limiting factor. Counting how many km someone can practically tour per year, this limits the frame lifespan to 5-10 years or max ~200 000 km.

Recommendations to extend the life of the aluminium frame:

• High quality design-manufacturing-welding can significantly last longer under same conditions, spend money on good frame.
• Protect from environmental conditions, don't leave outside in winter, protect from moisture when not in use.
• Ride with less weight.

A practical consequence for me that a second hand aluminium frame bike is risky, needs careful inspection of the frame for signs, and information how much the bike was used, how it was kept.

Some more interesting resources:

1. Fatigue design of welded bicycle frames using a multiaxial criterion (Procedia Engineering, 2012)
2. Fabrication and Fatigue Failure in Aluminum (Professional Boat Builder, 06 2012)
3. The formation of fatigue cracks in aluminum single crystals (Acta Metallurgica, 1961)
4. Fatigue Design of Aluminum Components and Structures (Hardcover, 1996)
5. Sporting Materials: Bicycle Frames (Encyclopedia of Materials: Science and Technology, 2001)
6. Parametric Finite Element Analysis of Bicycle Frame Geometries (Procedia Engineering, 20114)
7. What is fatigue failure and how can it be avoided?

Answer 3

There is an ISO standard test for bicycle frame fatigue testing, which manufacturers have to pass. Simply put it is 200,000 cycles of pedalling with a force of 1200N.

1200N at a typical 80rpm is a monstrous 2000W power.

Sprinting power is usually around 1000W, which is probably 60kph. At half the power, the cycles actually multiply by 10, due to the logarithmic relationship of the fatigue curve.

At that power, the frame will last 200,000 x 10 cycles. At 80rpm cadence and 60kph, it is equivalent to 25000km.

Realistically, a rider puts out closer to 400W, except for short sprints. Much of the time is spent even less than 200W.

As the fatigue stress vs cycles relationship is logarithmic, the frame lasts not just 5 times longer, but actually 10^4 = 10000 times.

A frame that has passed the iso test will be able to survive 200,000 * 10000 cycles of pedalling at 400W. At 80rpm cadence and 30kph, that equates to 12.5million km!

So yes, this is why manufacturers are happy to provide lifetime warranties on their frames.

Answer 4

The critical factor about aluminum frames is that virtually all aluminum alloys which are any good for building things are subject to "work hardening".

What this means is that, as a piece of aluminum is "cycled" in stress-release cycles, the aluminum tends to get more and more brittle. Steel does not exhibit this characteristic to anything near the same degree.

Example: Several years back I was camping on a tour. As I was assembling my tent one of the multi-segment aluminum poles developed a crack at end where the next pole "plugs in". Shifting around I got the tent assembled OK, but the next evening several more poles developed similar cracks, and by the end of the trip I needed to replace the entire set. The next year another camper in the group had the exact same problem.

It wasn't extreme stress that caused these cracks, but simply the "cycling" of putting the tent up and taking it down 50-60 times. Aluminum bike frames are made of better alloys and are more heavily built, but the same mechanism is at work, and even a frame which is not subjected to any extreme stress will get more and more brittle as it is used.

Answer 5

Having owned a 6061 alu frame ( marin larkspur hybrid bike ) with a lifetime warranty, and received no less than three warranty replacement frames ( each time after approx. 15k road miles ) all due to tubes that snap in half due to fatigue failure, i would strongly recommend against attempting repair on an alu frame. If one part of the frame is at the end of its life, so is the rest of the frame. There is a reason that every critical alu part of an aeroplane is replaced after a fixed number of flying hours, irrespective of whether it is showing any signs of wear and tear, and the reason is fatigue.

Answer 6

Data points:

• Cannondale Optimo: cracked downtube in under 2 years/12,000 km
• Trek 2.3: still okay after 10 years/70,000 km.
• Trek 1500: cracked drive side chainstay (age/distance not stated)

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Today my Optimo 63cm ( a Cannondale , pioneers of Aluminium bicycle frame... ) develop a crack around the diameter of the downtube, only 3 cm remaining holding the tube in one piece. Tired of the mis-shifting of the rear derailleur in danseuse mode, I stopped to check. And that’s when I see this huge crack... I just had to look at the right place. It’s a little scary , cause I just went down several hills at 65 km/h (40 mph).

Really didn’t think this would happen on a less than 2-year-old frame , with less than 12,000km.

At 6'4'' (193cm) , I'm only 180 lbs (82 kg). I also have an aluminum Trek 2.3 that is 10 years old and with at least 70,000km that has no frame problems. Its end is probably near but I was much more satisfied for its durability .

I must say that I had got it for replacing a series 1500 model ( entry level trek ) which had cracked its drive side chainstay. Yes the Trek 2.3 gives a rough ride and the Optimo is really comfortable in comparison. But I was close to finding hospital beds very uncomfortable for long term . I guess not all aluminum frames are born equal. I just hope that Cannondale have a warranty equal to Trek, I am waiting for the result of their investigation on my frame .

Answer 7

So far I preferred aluminium vs. steel for many reasons, but if steel lasts significantly longer, for my next touring bike I will go for steel.

Steel typically is slightly heavier but the increased durability is a great advantage. Also, steel is repairable. The problems of aluminum are its low fatigue life and the problem that aluminum needs to be heat treated after welding and that requires stripping all your components, stripping the paint, heat treat, reinstalling components and repainting, which is so expensive it's usually cheapest to just buy a new frame.

However, whether steel lasts longer than aluminum for you is a different question. If you buy a bike that has quickly obsoleted technology like e-bike technology, it may be that the electrics will be obsolete long before the aluminum frame has fatigued. Thus, not such a big problem to use aluminum on e-bikes. Also to cause fatigue failure, you need to not only use the frame for a large amount of kilometers, but also cause high forces on those kilometers such as being heavyweight, riding fast on narrow slick high pressure tires over curbs, and carrying heavy loads. Most cyclists may not use their aluminum frames long and hard, and thus it may appear they are durable enough but not for the heaviest uses.

For touring use the ability of steel to be repaired might be a genuine consideration.

Also consider safety: if a fork fatigues, you will crash. If a frame fatigues, you can usually limp home riding it carefully. So, for fork it is more important to use steel (or carbon fiber if you aren't afraid of the possibility of being damaged in a crash and then subsequently fail "just riding along", as carbon fiber doesn't have aluminum's fatigue problem but tends to be invisibly damaged in crashes) than for frame.

Especially if I use my bike both in winter and summer, as the heat change wear alu faster

I'm not convinced heat changes cause any problems for aluminum.

They say it can be welded, which will cost significantly less vs. a new frame (if it is available), but I should be prepared for other cracks to appear. The workshop contracts a welder specialized in bike frame welding and repair.

If the welding doesn't involve re-heat-treating which requires stripping all components away and repainting, then it's most likely a poor repair. Without heat treat, it will subsequently fail in a short time.

Answer 8

I worked with someone who was a bike designer at cannondale a few years ago. He had told me the frames were designed to be cycle loaded 1,000,000 times before failure. So that means the frame could be loaded to the full design stress one million times before failure.

Also welding a cracked frame is a VERY bad idea. The aluminum is heat treated. Welding it removes the heat treat and severely reduces the strength of the material. For 7005 aluminum that means going from 41,000psi tensile to 28,000psi. That is about a 30% reduction in strength.

Answer 9

So, so many variables with this, so it's hard to give a definitive answer. My Specialized Sequoia is 20 years old and has been ridden for tens of thousands of miles on generally good roads, though some of the roads around here are pretty 'rugged', so lots of bumps and potholes. There are oxidisation 'white veins' around the chain stays near the bottom bracket, and also around the insert holes on the seat stays. I'm guessing it's time I looked at a replacement. But just to reiterate: 20 years, tens of thousands of miles. Oh, and I live by the sea.

Answer 10

Frame of this bike is Cannondale's "Optimo" alloy. This tend to be lighter and stiffer, which provided thinner and more compliant frame build possible. I have heard many people with Optimo fractures, willing to go back to same again, since such a nice lightweight ride.... I didn't see any Furio frame cracking for instance... Its beefy and heavy 6061-T6 tubes don't make a race bike, but hell of stiff and lasting frame. These are just my 2c for consideration....