McBTC

Yeah but... an alloy fatigue limit of 500 million cycles? That's a lot of pedaling.

DrIsotope

I have no idea what they're using in their materials fatigue testing. Rod, bar, plate, Test Piece #7 , it wasn't specified. Though frames tend to fail at or near joints, not surprisingly-- and I doubt any aluminum frame would last even a hundred million cycles.

Though a few million starts to become a smaller number when blasting down a washboarded fire road at 25mph, with the frame absorbing multiple hits per second.

A buddy of mine races downhill MTB-- he chooses aluminum frames on purpose. Because he knows the frames will only last a couple of years (or crashes, whichever comes first) and the aluminum is much cheaper to replace than carbon.

Lazyass

The early aluminum frames like Vitus with small diameter tubes were well known for being too flexy. Some said that their bike would ghost shift when standing and climbing. Cannondale changed that and went with large tubes and reviews in the 80's said they were as smooth riding as steel if not more so. They even advertised that in their catalogs. I remember in 1988 or 89 a guy in the group I rode with bought a new Cannondale. He said on the first ride he had to pull over and see if he was losing air in the tires. I've had many aluminum bikes and I just never understood the whole deal with people saying they're too stiff. Tires and pressure have more to do with it than frame material. In the 90's I had a CAAD3 and all you hear about is those were the stiffest riding bikes of all time but that wasn't my experience. As long as you aren't running 20c tires at 120psi (like many of us were haha), then they're fine riding bikes.

If you rode a steel frame with fat tubes like aluminum bikes then your opinion of steel would change. There's a reason aluminum bikes don't look like the Vitus anymore.

McBTC

Probably most problems can be accounted for by having simply replaced steel tubing with alloy tubes but sticking with the traditional steel bike design instead of utilizing a frame design that maximizes the strengths and minimizes the weaknesses of the material used. For example, carrying the aluminum seat tube up above the top tube and stays, strengthened even more by an inner alloy seat post it seems to me would make sturdy enough junction to easily withstand 400 lbs.

McBTC

Many offroad bikes have been fabricated with 6061 that have been subjected without fatigue issues to far more abuse than any road bike will ever receive. Even with a steel frame, when you consider that most of such bikes are using alloy handlebars, seat posts, stems, steerer tubes, saddle rails, wheel rims, brake handles and calipers... it's hard to give much credibility to fatigue concerns.

McBTC

Concerning fatigue issues, to better optimize the use of the material, some reliable testing method was required--e.g.,

So, to get real world feedback, the testing is looking at frequencies of 1 /sec instead of 1,000 cycles per second.

https://web.wpi.edu/Pubs/E-project/A...Bike_Frame.pdf

While fatigue is an issue, it can be addressed and must be if we also wish to enjoy the benefits that the material's advantages can provide.

The research concluded as follows:

DrIsotope

Once again, you're trying to introduce your opinion as fact. I'm not talking about failure rate, I'm talking about (and here it is again) the fact that the failure point of aluminum is indistinct. At some impossible to determine point, an aluminum frame will fail. That is the nature of aluminum as a material. By the nature of that material, the failure stress point gets lower and lower as the part is subjected to more stress cycles-- until eventually, just a bump or bang, no matter how small, will trigger that failure point. No one can ever say when that will happen.

So to say there's no reason to give credibility to fatigue concerns... sure, fine. I don't have to ride your bike, so I'm 100% cool with your assessment. I don't ride aluminum frames because every one I've ridden has been harsh. Well, that and I broke my first one in 25 months.

Dean V

I would agree with you.
Also I would say that fatigue life shouldn't be a factor in the frame buying decision.
Any good quality frame should last a long time regardless of material.

McBTC

Just swaging it as a laymen but based on the numbers above, improving cycles from ~500k to 3.5M cycles, it seems to me you'd have an alloy frame that might not survive 10 century rides to a frame that's surviving ~4,000 century rides, especially if you consider that manufacturers did improve designs since the above testing by improving downtube shapes and sizes and frame-welding, aging and heat treating techniques.

Once talking about that kind of longevity, corrosion probably will be as big factor as fatigue when comparing the durability of steel vs. aluminum bicycle frames.

Racing Dan

Sure, but that imply your alloy handlebar, crank, stem, rims, ect will also fail at some indistinct point. > Good luck with your all steel "safety bike" ;-)

mstateglfr 

so what 'goes soft' on a steel frame? The tubes? The lugs? The silver braze? The brass braze?
all of it?

genuinely curious since i haven't seen it documented what goes 'soft'.

Racing Dan

I dont know what the mechanism is, but I do know (some) old steel frames become soft. Both I and a few friends have discarded frames for that reason.

Jack Tone 

Frame test: https://www.sheldonbrown.com/rinard/...tigue_test.htm

I've had my old Cannondale (version 1?) for about 25 years. I guess I should start worrying about it in another 25.

Trakhak

Subject: Frames "going soft" by Jobst Brandt

Racing Dan

And you can find at least 100 articles claiming carbon fibre have near limitless fatigue life as well. Does that mean all carbon fibre frames last forever? No.

Campag4life

No airplane rides for you...lol.
Flat earther? Just curious.

Don't tell Shimano, I hate it when those Al crank arms fly off and Al wheels fail precipitously. Glad it only happened to you...lol.

Don't put the wammy on us.

And guys, watch out for Al ladders. That last step is a duessy. Also start wearing a hard hat around the house. Those gutters can fall causing imminent death.

JohnDThompson 

I think that's more a rationalization for buying a new bike than an actual physical change in the frame itself.

Racing Dan

Why do you believe that? To me its weird ppl have such trouble believing a steel frame can alter properties with use. Im sure all of you are perfectly willing to acknowledge steel frames can and do crack on occasion. Do you really believe such frames are exactly the same up until the very moment they fail. Of course not.

McBTC

I smooshed the top/head tube butt in a front end collision-- that was the end of my old Panasonic cromo frame. My Trek frame was pretty corroded when I gave it away. I split the bottom of the head tube on a Scandium frame. I was worried about the seat post clamp arrangement on my CF frame the entire time I owned it. That leaves a lot of other bikes I've ridden over the years including both steel and aluminum frame MTBs that never had any kind of frame issues, including my first alloy road bike which I'm using now... tapered head tube and shaped top and down tubes and... it seems pretty bulletproof to me.

The only issues I've had over the years is a comfortable seat-- being a steel bike didn't help. I don't have that issue on my alloy road bike and that's with a 25mm rear tire.

Maelochs

Actually That is your opinion. Not every aluminum frame fails ... and given sufficient time Every frame will fail. There is no rust--proof steel.

Fact is, for Most riders, Al frames are lifetime frames. For most riders All bike frames (except maybe wood or bamboo, never looked at those much) are lifetime frames. There are always a few anecdotes about frame breaking ... steel, Al, CF, if you read enough posts here you will realize that Every frame is death waiting to grab you, and no frame material is safe. There are one or two people who have had unexpected, unexplained, catastrophic failures with Every type of frame.

Of course, there are millions of people worldwide who have never broken a frame, even during collisions. There are people (like myself) riding 35-year-old Al frames which show no signs of weakness ... and probably never will.

I realize, people who are afraid of ghosts get irritated when no one else gets afraid---they think that people are demeaning them.by refusing to fear ghosts they have never seen. This is not the case. if you have seen a ghost, and live in fear, that is fine.

I have never seen a ghost, and I cannot logically fear what I have no reason to fear.

I have steel, CF, and Al bikes and ride all of them without fear of catastrophic failure. You do what you do. Everything is fine.

But maybe, try to understand, that when you try to "prove" that riding bicycles is exceedingly dangerous, to a bunch of people who have been riding a lot, all their lives ... we haven't seen the ghost, so we cannot share your fears of it.

mstateglfr 

ok...not sure why thos was posted in response to my question to Dan, but it's been noted.

but hey- I'm also still confused as to the point of this thread too, so don't mind me.

Trakhak

From the Jobst Brandt piece that I linked to in my earlier post:

If these ideas [about steel frames softening with use] have been widely disproven, I'd appreciate knowing how. I've read all six parts of the FAQ and did not see it mentioned.

[Brandt's reply] The reason this was not in the FAQ may be that the whole subject is so preposterous to engineers, metallurgists, and physicists that they, the people who might explain it, are generally not inclined to bother discussing whether "the moon is made of green cheese" or not.

Racing Dan

But if the concept is "preposterous" then Im sure Mr Brandt can explain us why some steel frames crack without being crashed? (That even happens so Ti frames) That should be impossible if the unspoken presumption that the frame is never subjected to stresses beyond the fatigue limit, is true. Sorry, but clearly Mr Brandt failed to account for reality.

DrIsotope

The fundamental disconnect here appears that many in this thread are taking it upon themselves to argue against basic scientific fact. You're substituting random, confirmation-bias based conjecture in place of fact. The chance of failure based on material alone is higher for aluminum, based on the physical nature of the material. That is inarguable. What "you've seen yourself" is utterly meaningless.

A bicycle is not an airplane, a bicycle is not a ladder. Given enough time and enough duty cycles, everything made out of aluminum will reach a failure point. This point could come after your lifetime. It could come on Thursday. Saying "Oh, it's been same for <insert number of years> it should be fine for <insert number of years>" is wrong far beyond what is the basic logical fallacy that previous outcomes indicate future events. The physical nature of things is not subject to your opinions. "...shows no sign of weakness." Really? Are you paying any attention to the words you're putting forth?

I've also never once trended toward, or even hinted toward the idea of "fear of catastrophic failure." It makes absolutely no difference how long you've been riding, or what you do in your private time when you think about ghosts. Feel free to conflate fear and phobia. I don't care. You think that a delicate mixture of opinion and anecdotal evidence will somehow change the behavior of the physical world.

Lastly, catastrophic failure doesn't have anything to do with danger or harm to the user. If a seatstay or a chainstay or a downtube cracks/splits, the frame is ruined and the failure has been catastrophic.

McBTC

True, true... about, 'what does soft,' I didn't answer-- if anyone can but... my guess is that it's a weight-related perception. Depending on the size of the frame and the amount of butting, your steel frame can be ridden and never raise an issue but put 30 lbs. on the rear (say, going on a tour or maybe just put on a few pounds around the middle over the years), that steel frame can take on some 'whippy' characteristics that never existed before. Just a guess.