Life expectancy of aluminum

Understanding that aluminum frames continually degrade over time, whereas steel frames keep on rocking throughout time, what is a reasonable life expectancy for an aluminum freeride frame used on the shore? If there are no cracks, is it still worth it to upgrade components (seat, drivetrain, rear shock, brakes, stem, bar) on a 7 year old workhorse frame, and ride it into the ground? Or spend the bucks and buy a complete bike? Sometimes the frugality of your ride makes it that much more enjoyable.

I would say even if the fatigue life was still good, at 7 years old a new bike would have some advantages over an older one.

Better geo,weight and suspension are the 3 things that first come to mind.

On a safety aspect do you really want to find out how far you can push a frame till it breaks? Fine and dandy if a chainstay snaps and ends your ride, but when headtubes come off, it's rare to find a great place for it to happen.

I would say there is too many factors in trying to decide the life expectancy of a frame for anyone to come up with a solid answer.

I was told by an engineer 5 years for a bike framde

I was told by an engineer 5 years for a bike framde

curious how he came up with that number?

sooooooooo many variables(actually i think that so needs a few more o's)

It's not really a question that can be answered in absolutes. It completely depends on your frame.

Cycles in stress are what cause a fatigue failure. Think bending a paper clip back and forth. A bike will fatigue faster based on higher stress or a greater number of cycles.

So, the heavier you are, the more you ride or the harder you ride, the quicker your bike will fatigue and then break. Throw in different bike designs, different aluminum alloys, different heat treatments and it's pretty much impossible to predict when your frame is going to break.

And it is possible for steel to fatigue and break. It's just that steel has a fatigue limit. If the stresses are kept below this threshold, it will theoretically never break (due to fatigue).

Another thing to keep in mind is that fatigue failure is generally a result of the millions of small bumps and pedal strokes that you inflict on a bike over it's lifetime. The big hits contribute as well, but it's still possible to break a frame just by riding it a lot, pedalling and hitting braking bumps. It will take a long time if that's all you do, but it's still possible.

I was told by an engineer 5 years for a bike framde

LOL etc…

Just to add to Dirk's excellent response, there is a whole field of mechanical engineering focused on predicting the fatigue life of structures, mostly as applied to offshore structures, ships and aircraft. Typical analysis involves characterizing the loading distribution expected over the design lifetime of the structure in terms of the magnitudes of the loading and the occurrence frequency, then designing the structure to have some minimum "strength" at the end of that design life. So a bike frame may be designed for a 1 year life or a 10 year life, but obviously it would be easier to make a 1 year design life frame lighter… But, I doubt many bike designers can afford complete fatigue analysis of frame designs.

Interestingly, there is an effect where in certain conditions a periodic overloading can actually extend the fatigue life of structures.

Ah just LPI and eddy current your frame every year and you'll be OK. :nerd:

The engineer that designed your frame will have documented the design life of the bicycle. How accurate that is depends on how he estimated the loads and how much of a hack you are and a bunch of other things.

I would be interesting to know what design life they are shooting for, I could see that 5 year number thrown out above as being probably correct.

I would be interesting to know what design life they are shooting for, I could see that 5 year number thrown out above as being probably correct.

and that 5 year number may last one day for one rider and 15-20 years for another…..so at the end of the day it means nothing.

Periodically coat entire frame in JB weld until components don't fit anymore. Then retire it.

Good question though. After seeing those photo's of that Intense coming apart just behind the head tube, it is something that has been in the back of my mind.

Without any intentional threadjacking here, but along the same lines…..how often do you all change handlebars?

Doent the welding stress the aluminium, Planes are usualy rivited

Doent the welding stress the aluminium, Planes are usualy rivited

There are ways of relieving stress from welding. Heat treatment, etc.

Most modern aircraft will have welded aluminum structure in addition to rivets, so many rivets, stick in your shoe tread rivets.

Very true. The critical area is usually the area of highest stress (amplitute). In welded structures, (even after stress relief) the critical location is often close to the weld, and at the edge of a rivet hole in riveted structures.