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  1. #1
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    Aluminium frame fatigue

    Hey. I'm looking at an older mtb from around 95 or 96. Now I've heard that aluminium does fatigue over time and I'm quite a heavy person, around 280 pounds and I'm worried I'll just end damaging the frame. Anyone know anything? I only really drive on road, forest paths with some larger stones and roots and gravel roads.

  2. #2
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    true fatigue on alu bikes is super rare. typically when they fail it's because of a defect, even if it took awhile for it to manifest.

    One major concern with an aluminum mtb from the mid 90s has nothing to do with fatigue, though, is the fact that that was the weight weenie drillium era. LOTS of substandard bikes and parts were manufactured then (often drilled full of holes to make them lighter), and LOTS of stuff broke because it was simply too light and not durable enough. If it was a high quality lightweight bike for that era, I'd stay away.

    If it was a cheap, heavy aluminum bike, it'd probably be less risky from a durability standpoint, but the other issue with something of that age is its need for maintenance. If it had suspension, that's probably just trash at this point, and you're unlikely to find anything that will fit the bike now. So you'd have to install a rigid fork. It probably has other maintenance needs, too, and the costs will mount quickly.

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    A bike 10 years newer would be questionable. Thats a lot of years of someone doing god knows what to it.

    Definitely find a newer bike, thats far, far too old.

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    Quote Originally Posted by Harold View Post
    true fatigue on alu bikes is super rare. typically when they fail it's because of a defect, even if it took awhile for it to manifest.

    One major concern with an aluminum mtb from the mid 90s has nothing to do with fatigue, though, is the fact that that was the weight weenie drillium era. LOTS of substandard bikes and parts were manufactured then (often drilled full of holes to make them lighter), and LOTS of stuff broke because it was simply too light and not durable enough. If it was a high quality lightweight bike for that era, I'd stay away.

    If it was a cheap, heavy aluminum bike, it'd probably be less risky from a durability standpoint, but the other issue with something of that age is its need for maintenance. If it had suspension, that's probably just trash at this point, and you're unlikely to find anything that will fit the bike now. So you'd have to install a rigid fork. It probably has other maintenance needs, too, and the costs will mount quickly.
    It's a gt avalanche 96

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    Aluminum doesn't fatigue with time, but rather riding or the stress cycles that come from riding (loading and unloading). And Harold is right that aluminum is more susceptible to defect fractures induced by fatigue than steel.

    So, an old bike doesn't pose a problem in and of itself (other than the bad designs Harold also noted), but rather the amount of riding that occurred in it's long life. If you had any reliable way of knowing that it wasn't ridden much, it would be ok. Of course, you can't really know that.

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    Just stay away from the cannondales from that era.

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    Thanks everyone. I think I might have to reconsider. I just love the look of that old bike.

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    Quote Originally Posted by thesmokingman View Post
    Just stay away from the cannondales from that era.
    Was that the early-mid 90s? Besides being horribly stiff, did those break a lot? Assuming we're talking the first aluminum frames that Cannondale was mostly pushing.

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    Quote Originally Posted by TwiceHorn View Post
    Was that the early-mid 90s? Besides being horribly stiff, did those break a lot? Assuming we're talking the first aluminum frames that Cannondale was mostly pushing.
    Cannondale was notoriously bad early on with aluminum, hence all the joke names about them.

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    Quote Originally Posted by TwiceHorn View Post
    Was that the early-mid 90s? Besides being horribly stiff, did those break a lot? Assuming we're talking the first aluminum frames that Cannondale was mostly pushing.
    Their big thing was grinding down the welds for a "smooth look", it turned out to be counter productive and actually decreased the strength, probably because welds are not perfectly consistent, so if you grind them down to a consistent looking finish, the actual thickness would differ drastically in places.
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    I've seen quite a few cracked al rear triangles, down tubes, and seat tubes on mtbs ridden by fit experienced riders. These all happened after quite a bit of use.
    Do the math.

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    I agree with everyone else here about a bike that old for you considering your stated weight. I would also say that you should look for a bike that will give you more of an upright riding position, bars and saddle height being about the same height. The bikes of that era, in addition to the aforementioned, will have a more aggressive geometry with the bars lower than the saddle that may be uncomfortable for you. The end result being that you may not enjoy the hobby if you are uncomfortable on the bike. I would suggest looking for something newer. Have you considered any plus/ fat bikes?
    I don't know why,... it's just MUSS easier to pedal than the other ones.

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    I'd look at something from the last 5 years. An aluminum 27.5+ bike would probably work well for you.

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    Quote Originally Posted by thesmokingman View Post
    Cannondale was notoriously bad early on with aluminum, hence all the joke names about them.
    Yeah, I remember that pretty well in the context of road bikes. I just couldn't place the timeframe exactly, would have guessed late 80s, maybe earlier. Maybe it took them that long to get right with Al.

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    Quote Originally Posted by ChrisHoffmann View Post
    It's a gt avalanche 96
    GT from that era made very good bikes. I am still riding one. Just saying.

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    Quote Originally Posted by Jayem View Post
    Their big thing was grinding down the welds for a "smooth look", it turned out to be counter productive and actually decreased the strength, probably because welds are not perfectly consistent, so if you grind them down to a consistent looking finish, the actual thickness would differ drastically in places.
    I'm surprised at that because my engineering text says that a better surface finish improves fatigue life, the weld reinforcement does nothing to improve weld strength, and the step edge at the toe of the weld is a stress riser.

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    Quote Originally Posted by MikeDee View Post
    I'm surprised at that because my engineering text says that a better surface finish improves fatigue life, the weld reinforcement does nothing to improve weld strength, and the step edge at the toe of the weld is a stress riser.
    A good weld shouldn’t have a step edge at all; that’s a heat problem. Fillet welds should join the base material smoothly. I don’t ever grind my welds...

    But I’m also not an engineer.
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    Quote Originally Posted by MikeDee View Post
    I'm surprised at that because my engineering text says that a better surface finish improves fatigue life, the weld reinforcement does nothing to improve weld strength, and the step edge at the toe of the weld is a stress riser.
    A good weld shouldn’t have a step edge at all; that’s a heat problem. Fillet welds should join the base material smoothly. I don’t ever grind my welds...

    But I’m also not an engineer.

    Aluminium frame fatigue-f5df92e9-913e-4597-a323-f9be35ed14ac.jpg
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    Quote Originally Posted by Sage of the Sage View Post
    A good weld shouldn’t have a step edge at all; that’s a heat problem. Fillet welds should join the base material smoothly. I don’t ever grind my welds...

    But I’m also not an engineer.

    Click image for larger version. 

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    Do your fillets have a concave profile?

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    Quote Originally Posted by MikeDee View Post
    I'm surprised at that because my engineering text says that a better surface finish improves fatigue life, the weld reinforcement does nothing to improve weld strength, and the step edge at the toe of the weld is a stress riser.
    But it's not fatigue life that is in question, it's the limit, lower thickness or drastically differing thickness (because you ground it down) will create localized areas where the limit is significantly less. I'm guessing that maintaining constant weld thickness is very difficult to impossible when ground down like C-dale used to do. They may be able to handle stress up to that limit all day long, but if the limit is lower, it'll start a crack and that will progress with each subsequent cycle.

    Not only that, but grinding the weld to smooth it will introduce heat back into the metal and may change the properties of the weld, even if it "looks" all smooth. Control over that process would be critical.

    Assuming everything else is equal, I would agree that a smooth consistent surface finish when the wall thickness is constant and the heat and weld material are distributed evenly is the best outcome, but that's probably extremely hard to control given how thin the aluminum that is being welded is, which is also likely why a lot of manufacturers moved on to hydroforming to come up with more radical tube-shapes. I can't think of many applications where the welds are ground down and if one was doing so, I'm not sure how you would adequately control the thickness of the resulting material that is left.

    Bikes generally don't break from fatigue cycles, they break due to a flaw, under-designed part, or massive over-load. In the case of an under-designed part, it's a local over-load, but at or below the designed load limit for the entire bike. Again, that'll start a crack forming and eventually it'll snap one day.

    In the case of fatigue due to cycles, that'll usually take a long time, although a heavy guy on a 20+ old bike may be pushing it or at least needs to proceed with more caution.
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    Aluminium frame fatigue

    The grinding does not produce any significant heat. Cannondale used a small belt sander to grind down their welds.

    I agree on stress risers causing cracks, although I had two Gary Fisher frames that cracked and failed. I could see no reason for the cracks. The last one made by Trek is still going strong after a number of years. Go figure.

    I think the welding process is critical to preventing future cracking. What may look like a nice weld may not be. Too much heat damaging the tubing in the HAZ, subsurface defects, lack of fusion or penetration, etc.

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    Quote Originally Posted by MikeDee View Post
    The grinding does not produce any significant heat. Cannondale used a small belt sander to grind down their welds.

    I agree on stress risers causing cracks, although I had two Gary Fisher frames that cracked and failed. I could see no reason for the cracks. The last one made by Trek is still going strong after a number of years. Go figure.

    I think the welding process is critical to preventing future cracking. What may look like a nice weld may not be. Too much heat damaging the tubing in the HAZ, subsurface defects, lack of fusion or penetration, etc.
    Yeah, there's too much going on in a weld to apply the rule of thumb that "better surface finish increases fatigue life." That applies to a wrought or milled structure, not to a weld. Although, I suppose between two otherwise identical welds (ha), the one with better surface finish might have a longer fatigue life.

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    Quote Originally Posted by MikeDee View Post
    Do your fillets have a concave profile?

    Either slightly concave or flat.

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    Here's a timely article on the subject.

    https://www.velonews.com/2018/11/bik...fatigue_481150
    Do the math.

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    Quote Originally Posted by Lone Rager View Post
    Here's a timely article on the subject.

    https://www.velonews.com/2018/11/bik...fatigue_481150
    Yep, but IMO way too many people bought into the titanium thing back in the 90s, and the frames cracked as much as, or more than, anything else. It was because of the same basic idea above, frames don't generally fail from fatigue, it's very very rare, it's an under-designed part or flaw, which is overloaded and starts a crack, which many Ti frames succumbed to. The other failure is an overload above the designed limit, which starts the same process. The "theoretical" part of the material properties never really materialized IME. Not that there is no reason to get these, just that people made them out to be something they were not and lightspeed, merlin, lnysky and everyone else dealt with lots of cracked Ti frames.
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    So much facepalm in this thread. I don't even know where to start with some of you people.

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    Fatigue doesn't have to take 20 years, it all depends on the load cycles, geometry and material. You always have microscopic cracks at the welds, which could grow over time. Typically the strength is also significantly less at the HAZ. Basically I would just check the welds thoroughly each year. Actually found a couple of cracks on my last Canyon, so the frame was swapped on warranty.

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    I have an Easton Elite ProGram aluminum hardtail Kona from 96 that's seen thousands of miles. I've been around 220-240lbs for most of that time, currently at 260lbs. When it was new it was a pretty stiff ride. I noticed over the years that the frame became kind of a wet noodle during hard XC rides. Nowadays it seems like it's just too flexy to do any serious rides on so it's relegated to commuter status. I read alot of articles about aluminum frames fatiguing over years of flexing and I believe it.

    I would only buy that frame if you don't plan to do serious riding with it. I buy old bikes like that for nostalgic reasons and to ride around town or to a friend's place or the breweries.
    Last edited by Rodmunch; 4 Weeks Ago at 11:01 AM.

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    Quote Originally Posted by sonjaneufeld View Post
    have a look at best of steel https://www.bestofsteel.co.uk, there are great steel frames
    ...Door frames.
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    Last edited by D Bone; 4 Weeks Ago at 12:31 AM.
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    Spec sheet from flag pole manufacturer. The info give me confidence hopefully not false confidence. I ride a first generation 30 year old Cove Stiffee with a quarter size part where the paint flaked away so have a grey ashen look-


    6013 Aluminum

    Apparently my Cove spec with 6013 alloy with higher tensile strength than stainless steel. So hope to ride for forseeable future??

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    Quote Originally Posted by #1fan View Post
    Spec sheet from flag pole manufacturer. The info give me confidence hopefully not false confidence. I ride a first generation 30 year old Cove Stiffee with a quarter size part where the paint flaked away so have a grey ashen look-


    6013 Aluminum

    Apparently my Cove spec with 6013 alloy with higher tensile strength than stainless steel. So hope to ride for forseeable future??
    Dude, it's a 30 year old bike. Frames either fail in their first 1000 miles because they're not suited to the application (and that might be you) or there's a manufacturing problem... or the fail at >5,000 miles because lifespan. If they failed in the middle it's cuz you fuct up. Double bonus for carbon in this regard.

    TBH there's no reason to ride ANY 30 year old frame aside from commuter duty, so having it fail is a win. If you're riding it for its performance potential.
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    More info- my Cove been in storage for 20 years and just started riding again so probly hasn't seen 1000 miles. And according to the spec sheet 6013 "is virtually immune to exfoliation and stress corrosion cracking." So if I stop posting you can guess that Tele pole overpromised???

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    Airplanes have enjoyed decades upon decades of dependable aluminum dependability and successful operation.
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    Quote Originally Posted by Cleared2land View Post
    Airplanes have enjoyed decades upon decades of dependable aluminum dependability and successful operation.
    Shhhhhh, don't state such facts or you might ruin the new year for the plastic crowd.
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    Quote Originally Posted by Cleared2land View Post
    Airplanes have enjoyed decades upon decades of dependable aluminum dependability and successful operation.
    Wrong! They are routinely maintained and fatigued parts are replaced regularly. They even are super careful to isolate alu parts from carbon fiber parts to prevent galvanic corrosion from dissimilar materials.

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    Quote Originally Posted by thesmokingman View Post
    Wrong! They are routinely maintained and fatigued parts are replaced regularly. They even are super careful to isolate alu parts from carbon fiber parts to prevent galvanic corrosion from dissimilar materials.
    The topic of this thread is about the frame, not the components.

    Sorry, but your incorrect reply is only applicable only to rotable and replaceable components, not the core structural airframe that does not have the design ability that you have referenced of being replaced when is has exceeded its service life. Components typically do not endure the operational and structural stresses like the airframe encounters on a continual basis. The fuselage, empennage, stabilizers and wings are not replaceable components. These are the core of the airframe that must endure the ongoing stress of daily designed operations much like the intended design of a high-quality bicycle frame.

    And what does this topic of Aluminum Frame Fatigue have to do with galvanic corrosion?
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    Quote Originally Posted by Cleared2land View Post
    The topic of this thread is about the frame, not the components.

    Sorry, but your incorrect reply is only applicable only to rotable and replaceable components, not the core structural airframe that does not have the design ability that you have referenced of being replaced when is has exceeded its service life. Components typically do not endure the operational and structural stresses like the airframe encounters on a continual basis. The fuselage, empennage, stabilizers and wings are not replaceable components. These are the core of the airframe that must endure the ongoing stress of daily designed operations much like the intended design of a high-quality bicycle frame.

    And what does this topic of Aluminum Frame Fatigue have to do with galvanic corrosion?
    You are flat out making shit up. Alu fatigue is a serious issue with airplanes and there are serious regulations and measurements in this area. It's ludicrous that you imply that the aerospace industry just keeps jetting along with 30 year old aluminum as if they have some secret sustaining their alu for 3 decades.

    For ex.

    One of the most well-known aircraft accidents to occur due to widespread metal fatigue happened in 1988. The flight became so legendary that it was picked up by producers and turned into a TV film in the 1990’s called Miracle Landing.

    The inter-island flight, Aloha Airlines Flight 243, took a roundtrip course from Hilo to Honolulu, Hawaii. Everything about the trip began as normal, but along the way, the rapid growth of widespread metal fatigue cracks caused a portion of the roof to come completely off the aircraft.
    https://brightworkpolish.com/aviatio...ould-know-now/

    According to the Federal Aviation Administration, the LOV can be defined as “the period of time (in flight cycles, flight hours, or both) up to which it has been demonstrated by test evidence, analysis and, if available, service experience and teardown inspections, that widespread fatigue damage will not occur in the airplane structure.”

    Basically, the LOV is a measure of the amount of time a particular aircraft has before widespread metal fatigue becomes an issue. It’s a pretty important measure for several reasons.

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    You are diverting the topic.

    You're speaking out of your element.
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    Let's add more facts instead BS.

    A world-wide survey published in the International Journal of Fatigue in 1981, that that between the years of 1934 to 1981, a total of 306 aircraft accidents could be attributed to aircraft metal fatigue which resulted in 1803 deaths.

    Metal Fatigue and the FAA

    These types of crashes are much less frequent in modern times due to the FAA’s vigilance in determining accurate aviation limitations using the LOV parameters.

    In fact, the FAA requires both manufacturers and operators of aircraft to submit information about LOV levels according to a set schedule. These FAA rules have been in place since 2011 and operate to ensure that aircraft approaching maximum levels of cyclical loading and unloading can be retired well ahead of accidents and crashes.

    The FAA’s Aging Aircraft Program also plays a significant role in preventing accidents due to metal fatigue. The program began in March 2006 due to several concerns, including those brought on by the 1988 Aloha Airlines crash.

    Mainly, the Administration was concerned that many aircraft were being operated beyond their design limits and that a number of inspection criteria did not cover age-related issues for aircraft.

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    Quote Originally Posted by D Bone View Post
    Shhhhhh, don't state such facts or you might ruin the new year for the plastic crowd.
    ........ too late.
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    ^^^ That's funny!
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    I’ll go on record here as saying that core airframe components ARE serviced and ARE replaced during scheduled heavy overhauls. I participated in the removal and replacement of outer skins, inner structure, longerons and stringers on many aging commercial aircraft made by Boeing and by Douglas.

    Stress corrosion as well as dissimilar metal corrosion both accelerate fatigue failure of aircraft structures—aluminum, steel, magnesiumc—none are immune to it. The inspections mandated after the Hawaiian Airways plane crash revealed a pattern of structural failure that instigated new inspections, corrosion treatment and repair/overhaul procedures that gave work to many A&P mechanics like me.

    Any machine using these materials is susceptible to the same failures, including bicycles.

    Quote Originally Posted by Cleared2land View Post
    ...the core structural airframe that does not have the design ability that you have referenced of being replaced when is has exceeded its service life. Components typically do not endure the operational and structural stresses like the airframe encounters on a continual basis. The fuselage, empennage, stabilizers and wings are not replaceable components. These are the core of the airframe that must endure the ongoing stress of daily designed operations much like the intended design of a high-quality bicycle frame.

    And what does this topic of Aluminum Frame Fatigue have to do with galvanic corrosion?

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    Quote Originally Posted by Cleared2land View Post
    Airplanes have enjoyed decades upon decades of dependable aluminum dependability and successful operation.
    Quote Originally Posted by thesmokingman View Post
    Wrong! They are routinely maintained and fatigued parts are replaced regularly. They even are super careful to isolate alu parts from carbon fiber parts to prevent galvanic corrosion from dissimilar materials.
    My original post got completely turned around. My original statement is correct. Airplanes have enjoyed decades upon decades of dependable aluminum dependability and successful operation. This a fact.
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    Quote Originally Posted by Cleared2land View Post
    My original post got completely turned around. My original statement is correct. Airplanes have enjoyed decades upon decades of dependable aluminum dependability and successful operation. This a fact.
    Planes have not enjoyed dependability and success with aluminum. Stop making shit up.

    A world-wide survey published in the International Journal of Fatigue in 1981, that that between the years of 1934 to 1981, a total of 306 aircraft accidents could be attributed to aircraft metal fatigue which resulted in 1803 deaths.
    Other notable crashes due to metal fatigue include the Comet jet crashes of the 1950’s. Comet jets, as many aircraft enthusiasts may already know, are the famous British precursors to the era of U.S. Boeing 700’s which began cornering the market in the late 1960’s.

  46. #46
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    The comet jet was a flaw, stress riser created a crack that propagated with cycles. That's an under-stress failure. That's not because they went and flew the plane a bunch or because aluminum sucks, that was a design flaw.

    The Hawaiian issue was because they flew the plane and loaded the airframe it in a way that was not intended, so it "aged" the aircraft much quicker to do all those short turns, that was much less on the "design flaw" side of things. So that would be like riding your bike hard several times a day every single day, which most people don't do, a 20 year old thin-wall aluminum hardtail might reach it's fatigue life much quicker doing this, but it's not really relevant.

    The issue remains that an aluminum bike just sitting there in a controlled environment is going to be fine, the number of cycles you'd have to put on it usually make it highly unlikely it'd fail due to fatigue life and unless you overload it or there was a design flaw, it should give years of good service. Just because it was from 1996 doesn't mean it's at risk of imploding. In the case of airplanes, maintenance and inspections are required to ensure the airplane remains airworthy as fatigue is concerned. In the case of a bicycle, it's that there wasn't an underlying flaw to start with and it wasn't over-stressed as far as the big concerns.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  47. #47
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    A thick aluminum frame would have what basically amounts to an infinite fatigue life... But no one makes big thick frames, it's too heavy. We're looking at 4-7lb of aluminum.

    Sure, we mostly see overload failures, but that changes nothing. I wouldn't want to ride an old aluminum frame. They absolutely do break!

    The 90's saw poor quality paper thin frames that broke. The early 2000's was the bender era where hucking to flat was cool, and those broke too. Fatigue, abuse, or just design flaw all played roles, but still, pass on that.

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