Mountain Biking - How 'old' of a used aluminum-framed bike would you buy?

OK, OK; I know that's a tough question and maybe boils down to 'it depends' but I'm curious as to how old of an aluminum bike you would even consider. Sure, there's going to be lots of variables like how many miles on it, what kind of use/abuse, what brand and style of bike/frame, ..... . But it seems there would be a point where a certain number of years of age are going to make an aluminum-framed bike (let's not get into vintage steel, etc right now) probably not a serious contendor for a purchase because of general frame fatigue, as well as obsolete or older frame design and components.

At what point in number of years old would you not buy an aluminum-framed FS xc or all-mtn bike in well maintained (not beat, some scratches, all original components, 'average' use and mileage) condition even if the price seemed fair because you would be concerned about general metal fatigue and outdated components?

The old rule of thumb for a race career hardtail was 5 seasons. Since then, they have developed better frames, but tougher courses and crazier people. I see frames crack in 4 yrs racing nowdays(including mine,but I fix it when that happens) and a lot less in freeriding. My friend who was a 100 lb freerider had his FS frame crack in a little over a year. Not the best frame but it wasnt junk either. Generally FS frames will last longer than HT, inasmuch as they have give. The use profile for FS anymore tends to belay that benefit though, so you should make sure what its been through.
I would say if it had a tame life, I would still buy it at 4 or so yrs. Especially a company like Giant(a few others do to) that has a lifetime warranty program. Unless you race a Giant, you can have it replaced if it cracks out.

I should also note for really anyone with aluminum frames, keep the frame thoroughly polished, especially at joints. The act of polishing is in itself an inspection means, and it has found more than a few cracks in my experience. No failure is sudden in frames, it is all a progression. For a head tube to fly off a frame it had to be cracked for a long while. It is especially important for High-timed frames. With that in mind I will run a frame until it can't be, but I am used to the inspection means as a job.

Geez you have a new pic every week haha

I would generally follow the same rules as laid out above. However I tend to not buy used. I look for closeouts before used is an option. Out here, every bike is basically wrecked with the amount of ride time put on.

Geez you have a new pic every week haha

:D

Good points! For one example, there's a 4 or 5 yr old Specialized FS at a local shop that looks really nice, a trade-in. LBS says it's hardly been ridden; 'it's almost like a new bike'. But it's obviously had some use and the design/componentry are dated. Sure, it's 1/4th the cost (or less) of a new bike and a person could walk out with it for virtually peanuts but does that really make it a good buy? I tend to say it might be fun to bang around on at this point but I'm not so sure I'd want to go flying down the trail on it.

Mythbusters: I've heard from several directions (although I tend to not believe it) that an aluminum frame will lose some of its integrity simply as a function of time; sort of an 'aging' process. Any truth to that?

over 10 yrs. i'd stay away from...

THere may have ben some element of truth to the core of the statement.
The process that makes a frame crack is not in fact a weakening but a hardening. 'Work hardening' is the techincal term. The more a metal is cycled, or pounded the harder it gets. The side effect of this of course is brittleness, the tendency to crack rather than bend. The bigger problem is that this effect concentrates at the points of highest stress, welds. This is why if it is a crack in the front triangle, I will treat it with major caution, unlike a rear brake mount or rack mount(which I reattach). When something large and uniform such as a top tube weld begins to go, it is likely that the rest of the triangle is not far off.
In aviation, where we use aluminum extensively, we will sometimes counteract this effect by 'anealing' the metal as a re-heat treatment. This process will bring the frame to a uniform strength, essentially what it was mint.

THere may have ben some element of truth to the core of the statement.
The process that makes a frame crack is not in fact a weakening but a hardening. 'Work hardening' is the techincal term. The more a metal is cycled, or pounded the harder it gets. The side effect of this of course is brittleness, the tendency to crack rather than bend. The bigger problem is that this effect concentrates at the points of highest stress, welds. This is why if it is a crack in the front triangle, I will treat it with major caution, unlike a rear brake mount or rack mount(which I reattach). When something large and uniform such as a top tube weld begins to go, it is likely that the rest of the triangle is not far off.
In aviation, where we use aluminum extensively, we will sometimes counteract this effect by 'anealing' the metal as a re-heat treatment. This process will bring the frame to a uniform strength, essentially what it was mint.


Thanks for the info! I like knowing the technical side of things. :D