Off topic again for a minute...
@Golgo13 you might be just the guy to clear up a misconception I have had for years. In the high end custom mountain bike world there has been this belief that after 10 years an aluminum mountain bike has reached its max useable life, even if it was never ridden. I can’t tell you how many times I have seen guys say, “nope don’t buy that frame it only has a few years left”. But I always thought it was just marketing mumbojumbo to get people to buy new. Does aluminum like our wheels or mountain bike frames have a service life if the max impact/deflection/load is kept at a % under max?
The concern is that the aluminum is "aging," which depending on who you talk to you will get a different answer. For thin materials, a certain amount of atmospheric oxygen is diffused into the material causing brittleness. This is observed in thin panels used for stamped parts pretty frequently. With "fresh material" if you try to make a 180degree bend with a tight radius, usually it will be OK. With aged material, it is susceptible to cracking instead of deforming/bending like you want.
The idea with the bike frame is(even with paint/powdercoating) this still happens. In general, aluminum doesn't fatigue very well. Its not quite as elastic as steel can be. So when you combine that with the aging, yeah, a bike frame would have a useful life.
I did read many moons back that, Japanese alloys (OEM and aftermarket) have to sustain some pretty serious testing before being allowed to be sold, mine are 23+years old and no issues to date. The lacquer peeled off and I had them refinished, during the sandblasting they were checked for any hairline cracks but all good.
I do get the occasional porous alloy (insert brand here) but generally most are pretty good, Land Rover alloys on the other hand do crack, even without any off road use, ask me how I know!
In the event of serious damage an alloy loses out to steel wheels which can be beaten back to shape, something an alloy will not tolerate .
Regards
Dave
Back on this topic, Japanese alloy wheels, in order to be sold in Japan, have to pass the JWL testing standards (thats the weird little logo on the wheel face). Their strength/durability targets are a little more severe than US-DOT requirements, but not much. There IS a special off-set impact test done for JWL-T, when required for a "truck".
In regards to porosity, all cast wheels have a certain degree of porosity in different areas. It is the wheel manufacturers responsibility to manage where the porosity forms during casting and to keep the size of the pores limited within certain material standards. As long as the design of the wheel allows for it, the porosity doesn't necessarily cause any harm. It just results in areas where strength is lower and more material is needed to make up for it.
In regards to the strength/durability of the wheel, a good design balances the expected life of the wheel with mass to prevent using too much material for something where it isn't necessary. The engineer decides this based on vehicle mass, handling limits, etc. Then he creates a template for a stylist to ignore and has to spend months fighting for styling surfaces to change until his targets are met for strength and durability. For those of you who think a good wheel should last forever, keep in mind, if you apply that philosophy to its extreme, you would just have a solid chunk of aluminum bolted to your vehicle and that would be boring. Plus the added mass feeds back into suspension loads on the vehicle and then the suspension needs to be beefed up. The cycle of adding mass where needed to achieve infinite life would only end when the vehicle has so much steel in it there is no place for an engine or room to sit inside. This is an exaggeration, of course, but you get the idea.
Finally,
@Dave 2000 makes an excellent point that a steel wheel can be bent back into shape with a hammer. I don't care what the repair guy tells you or what your personal experience is, a bent or cracked aluminum wheel cannot be repaired. That is why the owner's manual of nearly every vehicle tells you not to repair them. It isn't to sell wheels, its to prevent a later, more catastrophic failure.
Side benefit of being in the biz, left over magnesium makes for epic camp fires.
