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

[Removed extra questions to be clear.]


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.


Topics I have researched:

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

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

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How long an aluminum bike will last depends on many many factors. There is already a question on steel versus aluminum for touring. Why does there need to be a significant difference? What are the many reason you prefer aluminum over steel in a touring bike? –  Blam Jul 10 at 13:29
3  
Depends on the quality of the frame's construction. Depends on the exact alloys and thicknesses and construction practices. Depends on how roughly you ride the bike, over what kinds of terrain and obstacles. I doubt there's a solid answer other than trying to do a large-scale statistical survey. Personally, I refuse to worry about it. –  keshlam Jul 10 at 13:31
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Your aluminum bike cracked but you still prefer aluminum because is corrosion free and no worries to paint. If corrosion and paint are your priority then by all means you should get an aluminum bike. –  Blam Jul 10 at 16:02
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Regarding the research article you found, there was general corrosion all over the inside of the frame, blamed on the humid, saline environment it was used in (somewhere in Spain presumably). There's also stress corrosion cracking (en.wikipedia.org/wiki/Stress_corrosion_cracking) and clear evidence of fatigue. The Al alloy is AA7005, and has been over-aged. –  blochwave Jul 11 at 11:11
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@mattnz No aluminum does not rust just a much as steel. Have you ever seen rust on an aluminum can? Aluminum corrodes but it does not rust. Rust refers only to iron and steel corrosion. Aluminum corrodes but it does not rust. However, aluminum corrosion is aluminum oxide, a very hard material that actually protects the aluminum from further corrosion. Aluminum oxide corrosion also looks a lot more like aluminum (dull gray to powdery white in color), so it isn't as easy to notice as rusted iron. –  Blam Jul 11 at 15:57

2 Answers 2

up vote 11 down vote accepted

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.

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Thanks a lot for the points! I removed the extra questions to be clear. Of course the old bikes from my father were from steel. –  olee22 Jul 11 at 5:02
    
+1 for titanium! If it weren't so expensive and hence unsuited for commuting (because of the need to leave it out in public)... –  arne Jul 11 at 5:15
    
Steel does fatigue eventually, it just takes much longer. There is always a tradeoff in weight/durability regardless of the material. –  Fred the Magic Wonder Dog Jul 11 at 14:48
    
@FredtheMagicWonderDog Well.... mild steel will not normally admit fatigue crack growth if the applied stresses are below about 10% of the strength of the material. –  Blam Jul 11 at 14:57
1  
High end "steel" bike tubesets don't really have much in common with typical steel alloys. Back in the old days when steel was the only option, cracked frames on high end racing bikes was common after 50-60K miles. –  Fred the Magic Wonder Dog Jul 11 at 15:08

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.


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?
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