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With the current state of aluminum alloys used in bike frames, is fatigue still an issue over a reasonable number of miles? Is an alu frame still as stiff after 20k miles, and is it more susceptible to failure? Or is the expected lifespan much higher than those hypothetical numbers?
 

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too many assumptions to say anything

any of the subtances used for frames today can have all or most of the properties we desire, including longeivity. depends on metallurgy and engineering, and physics.

just don't buy an 80s bonded Vitus, LOL

article by Sheldon Brown from many years ago on a bunch of different frames tested - results were the alu Dale turned out to be the longest lasting frame, out of a bunch of alu, carbon and steel frames tested. Frames of all type have only gotten better since. https://www.sheldonbrown.com/rinard/frame_fatigue_test.htm
 

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too many assumptions to say anything

any of the subtances used for frames today can have all or most of the properties we desire, including longeivity. depends on metallurgy and engineering, and physics.

just don't buy an 80s bonded Vitus, LOL

article by Sheldon Brown from many years ago on a bunch of different frames tested - results were the alu Dale turned out to be the longest lasting frame, out of a bunch of alu, carbon and steel frames tested. Frames of all type have only gotten better since. https://www.sheldonbrown.com/rinard/frame_fatigue_test.htm
Excellent info :thumbsup: !


I happen to own two early Cannondale framesets :cool: .
 

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For what it's worth, I have an aluminum '06 Fuji Newest 3.0 that I bought and started riding in early '07, my first modern-day road bike. According to my records, it has 28,774 miles on it. It's my weekday and back-up bike. So far, so good.
 

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With the current state of aluminum alloys used in bike frames, is fatigue still an issue over a reasonable number of miles? Is an alu frame still as stiff after 20k miles, and is it more susceptible to failure? Or is the expected lifespan much higher than those hypothetical numbers?
You appear to be conflating/confusing things. In order for an Al (or any other) frame to go "soft" it must have experienced serious fatigue damage. Absent a crash, a grossly heavy and strong rider, or an attempt to go well beyond the design limits of the material, no frame is going to go soft after 20K miles. Aluminum does not have a fatigue limit, so it will always be heading toward fatigue failure, unlike steel, Ti, or CF so yes it is "more susceptible to failure" but a properly designed frame used within reasonable bounds is not an issue for most riders and riding conditions.
 

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Discussion Starter · #8 ·
You appear to be conflating/confusing things. In order for an Al (or any other) frame to go "soft" it must have experienced serious fatigue damage. Absent a crash, a grossly heavy and strong rider, or an attempt to go well beyond the design limits of the material, no frame is going to go soft after 20K miles. Aluminum does not have a fatigue limit, so it will always be heading toward fatigue failure, unlike steel, Ti, or CF so yes it is "more susceptible to failure" but a properly designed frame used within reasonable bounds is not an issue for most riders and riding conditions.
Very interesting, thanks.
 

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With the current state of aluminum alloys used in bike frames, is fatigue still an issue over a reasonable number of miles? Is an alu frame still as stiff after 20k miles, and is it more susceptible to failure? Or is the expected lifespan much higher than those hypothetical numbers?
20,000? bruh. they bend over time. I think there's an assumption that aluminum frames are somehow infinitely stiff, but the truth of the matter is that "compliance," as a function of quality of the aluminum material, is built into all aluminum frames. they bend as soon as they come off the line. and the more significant use they get over time, they more they will bend over time, or the more "compliant" you will find the ride becomes. you don't have to be a physicist to understand those basic principles. aluminum bends.
 

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maybe by 200,000 miles it might become noticeable

and don't discount the alloying they do to change the metal from behaving very much unlike pure aluminum. not to mention the tube dia/shape/thicknesses used to achieve maximum longeivity and comfort
 

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they bend over time. they bend as soon as they come off the line. and the more significant use they get over time, they more they will bend over time, or the more "compliant" you will find the ride becomes. you don't have to be a physicist to understand those basic principles. aluminum bends.
Really? Got any evidence to support this claim? Because if the frame is not stressed beyond it's fatigue limit, it doesn't bend. If flexes (just like steel, Ti, or CF) but it does not bend.
 

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With the current state of aluminum alloys used in bike frames, is fatigue still an issue over a reasonable number of miles? Is an alu frame still as stiff after 20k miles, and is it more susceptible to failure? Or is the expected lifespan much higher than those hypothetical numbers?
There's something you have to remember about aluminum: it has no endurance limit. This means that there is no minimal amount of stress it can experience below which an infinite number of cycles will not cause failure. In layperson's terms, if you flex an aluminum frame just a hundredth of even a thousandth of a millimeter enough times, it will fail. The greater the stress it experiences, the fewer cycles required to cause failure.

This is not the case with steel and titanium. With these metals, there is a amount of stress below which an infinite number of cycles will not cause failure.

So what does this mean in the real world? Technically speaking, every aluminum frame will fail if you ride it enough. But how much is 'enough'? Depends, I suppose on a lot things. An aluminum frame built to flex will likely fail sooner than one built to stay maximally rigid. There are other factors, however. Defects in the tubing. Quality of the welds. Stress risers caused by machining parts and mitering the tubes, etc. All of these can make any frame fail, and in the case of aluminum, likely a lot sooner than its non-existent endurance limit would.
 

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There's something you have to remember about aluminum: it has no endurance limit. This means that there is no minimal amount of stress it can experience below which an infinite number of cycles will not cause failure. In layperson's terms, if you flex an aluminum frame just a hundredth of even a thousandth of a millimeter enough times, it will fail. The greater the stress it experiences, the fewer cycles required to cause failure.

This is not the case with steel and titanium. With these metals, there is a amount of stress below which an infinite number of cycles will not cause failure.

So what does this mean in the real world? Technically speaking, every aluminum frame will fail if you ride it enough. But how much is 'enough'? Depends, I suppose on a lot things. An aluminum frame built to flex will likely fail sooner than one built to stay maximally rigid. There are other factors, however. Defects in the tubing. Quality of the welds. Stress risers caused by machining parts and mitering the tubes, etc. All of these can make any frame fail, and in the case of aluminum, likely a lot sooner than its non-existent endurance limit would.
Here is my thought given the anecdotal evidence around us. Its been a lot of years since the heyday of Al bikes. Yet, we don't see posts on RBR saying "my AL bike broke!" or "my frame went soft". So while I agree that Al deteriorates with every stress cycle, it would appear that the number of required cycle to failure is well beyond the typical use of an Al frame
 

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Discussion Starter · #14 ·
There's something you have to remember about aluminum: it has no endurance limit. This means that there is no minimal amount of stress it can experience below which an infinite number of cycles will not cause failure. In layperson's terms, if you flex an aluminum frame just a hundredth of even a thousandth of a millimeter enough times, it will fail. The greater the stress it experiences, the fewer cycles required to cause failure.

This is not the case with steel and titanium. With these metals, there is a amount of stress below which an infinite number of cycles will not cause failure.

So what does this mean in the real world? Technically speaking, every aluminum frame will fail if you ride it enough. But how much is 'enough'? Depends, I suppose on a lot things. An aluminum frame built to flex will likely fail sooner than one built to stay maximally rigid. There are other factors, however. Defects in the tubing. Quality of the welds. Stress risers caused by machining parts and mitering the tubes, etc. All of these can make any frame fail, and in the case of aluminum, likely a lot sooner than its non-existent endurance limit would.
My instinct told me to be skeptical of "compliant" AL frames. For example, the Trek Domane ALR with its flexing Isospeed seattube always looked like a candidate for early failure. Same for the SAVE suspension built in the rear triangle of some AL Cannondale models. But I guess the manufacturers were smart enough to stress test those parts and make sure they won't fail within the useful life of the bike...

Envoyé de mon XT1563 en utilisant Tapatalk
 

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I've seen cracked aluminum frames, most of the MTB's. I've never cracked an aluminum frame and I've had a few Cannondales. I cracked an aluminum seat lug on a steel tube bonded Raleigh. I drilled a hole through the lug and post and bolted it in place so I could use it until the warranty frame arrived. If you're racking up the serious miles and racing, a lightweight aluminum racing frame will get you 2-3 seasons. A more robust aluminum frame will last for decades.

Submarine hulls are made out of steel because of the long cyclic stress life. A hull has a certain number of years/dives before it has to be recertified but that is typically around 25 years. The Soviets built submarines with titanium hulls because the metal is abundant in Russia. The hulls developed cracks and had all kinds of quality issues. You wouldn't build a submarine hull out of aluminum.
 

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I'm riding a Cannondale CAAD 7 bike that I bought new around the end of 2003. The bike is stock except for some compact gearing I put on recently. Frame now has over 70,000 miles on it including a couple gnarly crashes. I even dented the top tube on both sides from the bars swinging around and hitting it on my very first ride, and I've ridden it that way ever since. Bike is still super stiff in sprints, comfortable enough over rougher roads, and I've never had even a hint of problems.
 

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To me, you just don't get any warning with AL. I raced an AL frame for probably 10 years. One day I thought the BB lug area needed cleaning of road gunk and dried up Gatorade. On closer inspection the seat tube had actually started to "tear" away from the bottom bracket cluster. You know those guys who can sometime tear open beer and soda cans? Well the AL tubes used in these frames are not that much different.
 

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But you do. The aluminium has developed a crack, and you discovered it prior to it reaching critcal, or runaway length, and that's the warning. You won't get this with composite frames, where it usually fails catastrophically, without any warning.

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I've seen cracked aluminum frames, most of the MTB's. I've never cracked an aluminum frame and I've had a few Cannondales. I cracked an aluminum seat lug on a steel tube bonded Raleigh. I drilled a hole through the lug and post and bolted it in place so I could use it until the warranty frame arrived. If you're racking up the serious miles and racing, a lightweight aluminum racing frame will get you 2-3 seasons. A more robust aluminum frame will last for decades.

Submarine hulls are made out of steel because of the long cyclic stress life. A hull has a certain number of years/dives before it has to be recertified but that is typically around 25 years. The Soviets built submarines with titanium hulls because the metal is abundant in Russia. The hulls developed cracks and had all kinds of quality issues. You wouldn't build a submarine hull out of aluminum.
Keep in mind that it takes more skill to work with titanium than it does steel. Man has a long track-record of building large objects with steel. So a submarine is no stretch for mankind's skill with the metal. Not so for titanium. It's easy to see why they'd screw up titanium submarines.

I agree with you that a robust aluminum frame can last for decades, and that an ultralight aluminum frame ridden hard will not. But what you're forgetting is that in the real world, other things are more likely to make a frame fail than the material of the tubing, such as the items i mentioned above such as welds, machining, mitering, etc.
 

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My instinct told me to be skeptical of "compliant" AL frames. For example, the Trek Domane ALR with its flexing Isospeed seattube always looked like a candidate for early failure. Same for the SAVE suspension built in the rear triangle of some AL Cannondale models. But I guess the manufacturers were smart enough to stress test those parts and make sure they won't fail within the useful life of the bike...

Envoyé de mon XT1563 en utilisant Tapatalk
Everyone at Cannondale has s*** for brains. They have a long track record of pulling designs out of their backsides that the rest of the bike industry can see are crap. Gimmicks meant to sell bikes and nothing more. They are the epitome of a company that thinks out of the box for the purposes of thinking out of the box and separating its products from others to maximize sales. They haven't contributed anything to the industry.
 
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