I have a degree in mechanical engineering and I am amazed at the ignorance being spouted on here as if it were fact. Aluminum is a great material for mountain bike frames and is not likely to fail during the life time of most riders. That's why it is used for the vast majority of mountain bike frames. If you are afraid of aluminum, you should not ride a bike, given that the handlebars, cranks, rims, stem and other vital components are most likely made out of it. (Imagine what would happen if your stem or handlebars were to break suddenly).

There is a lot of confusion about fatigue limit. It is true that steel is better in this regard than aluminum, but it still doesn't make steel superior to aluminum in every application. Steel is not indestructible and many steel frames have broken in the past. So a picture of a broken aluminum frame proves nothing. I like steel frames (5 of my 6 bikes are steel) but I wouldn't hesitate to ride an aluminum frame if it were built by a real bike company (like Trek) and not bought from a department store.

PS - It is especially telling that the "The ARS", who is spouting so much nonsense, doesn't know that almost every airplane out there is made of aluminum. Please Mr ARS, go to an airport and find me just one steel airplane. Just one. I'm waiting...

Just because you see failed aluminum frames on the 'net doesn't mean that aluminum is significantly more prone to failure. How do the sales numbers stack up between aluminum and steel bikes nowadays? If aluminum outsells steel and has comparable failure rates, wouldn't it make sense that we'd see more failed aluminum frames?

Engineering is an art of compromises and any material can fail depending on which compromises are made. Want a bike that's impervious to frame failure? Sure, but it'll probably be a bit on the heavy side, whether it's made from aluminum or steel. Want a bike that's lightweight? Sure, we can do that, in a number of materials. But it'll probably be a bit more prone to failure since we'll push the envelope a little bit to get it juuuust that much lighter. Want that bike to be stiff, too? And without being too expensive? No wonder aluminum's so popular.

OK, but only since you asked so nicely...

Aside from the absolute newest composite designs, most modern airframes are built primarily from aluminum. A Boeing 747-400 is made of 74 tons of aluminum. The Boeing 777 is 50% aluminum. The structure of the brand-new Airbus A380, the largest airliner in the world, is 61% aluminum. 80% of an F-16 fighter's structure is aluminum. B-52 bombers are primarily aluminum and have an estimated service life of 37,500 flight hours -- about 4.25 years in the sky -- before metal fatigue becomes a concern.

Thanks for that post. There seems to be an theme that some have spread that Trek, Giant, Specialized, Jamis, Haro, Raliegh and Lapierre decided to design MTBs strictly by marketing without the help of engineers, pro riders and testing facilities. Then they disreguard the experience of multitudes of riders and customers that have successfully bought and used the machines developed by those same companies. About a month ago I was looking for a back up bike and started hunting for a more classic or vintage bike that I could at least put STI shifters on and a 130 rear spacing. I happened upon a 91 Klein pre-Trek. This bike was like new even after 22 years. Gary Klein was from MIT and should know something about frame material and the result was a classic Quantum with full Dura Ace 7403 front to rear. I was a bit worried about how the ride would be but with hand built wheels and 32 spokes it is just fine. Klein was right a quality long lasting bike not only could be built from Aluminum he built several. I still smile when I ride the Klein on weekends.

Most hardcore mountain bikers are not 240 lbs. Having said that, I said 'may be more suitable' because I'm not a frame material's expert. Perhaps an aluminum frame would last with a 240 lb rider going over obstacles???

Yes Alf, yes it would. Not that clydes aren't harder on equipment, but aluminum is a perfectly fine choice for them.

Got a mate that weighs 240 lbs and a Giant Boulder bought in 2000. Took him 9 years to break it and that was aggressive Offroad af about 2 to 3,000 miles a year.

Right on.

If the OP was asking about replacing a '70s or '80s aluminum frame I would say yes, definitely, but even then it would be less about the inherent fatigue characteristics of aluminum and more about the improvements in alloys and manufacturing processes.

I would recommend riding one of GT's classic steel triple triangle frames before buying the Trek. There's certainly nothing wrong with a steel Trek, but I've always preferred the feel of the GTs. And they look cool. I occasionally see them turn up dirt cheap on Craigslist, but rarely in my size.

Most modern aircraft have a mix of aluminum and carbon fiber structural components.

I never see any steel GTs mine is '01 and it is a triple triangle frame. That feature is one reason I think may help my bike last some time. Whenever I get another bike it will be new, since I've already done the used craigslist way with the bike I currently own.

If you want new there's nothing wrong with that, but there's also nothing wrong with riding a used (properly inspected, good condition) steel frame of any vintage you're likely to find.

Google didn't turn up a Darby CL, and I don't know Pa. geography well enough to know what's near you. Found these with a quick search of the Philly CL:
https://philadelphia.craigslist.org/bik/2988799400.html
https://philadelphia.craigslist.org/bik/2920560510.html
The posters didn't list tubing spec or provide pictures that would should the details, and since it's not near me I didn't go hunting to find out.

I've had two frames fail on me. Both were steel. But then, I've never owned an aluminum frame.

One was a Montgomery Ward 10 speed, its downtube pulled out of the bottom bracket while I was riding along a bikepath. Suddenly the bicycle felt soft like a Claes Oldenburg sculpture. The other was a Diamondback Ascent and one of the dropouts cracked.

Thanks, Upper Darby is right next to Philly.

Ive been looking on Craigslist and it seems when I find bikes that are nice and steel that they aren't my size. I bought my current bike off of Craigslist and would love to find the right bike at a discount. Frustration from looking is making me lean toward new.

Ive heard that steel can fail but only with rust, crashing or a lot of abuse. What caused your bikes to fail?

Words, you heard wrong. It's fine that you want a steel bike, but don't justify it with message board BS that aluminum is an inferior material. Any bike can fail. The vast majority (of any material) won't, under normal usage. And yes, a 250lb person rolling around on bike paths and fire roads and even single track is normal usage.

Cheap department store bike which probably failed due to a poor weld.
I have an Ascent. I generally like DiamondBack's pre buyout stuff (and I love the old Centurion road bikes). Was there any unusual stress to cause the brake?

These problems could all have been resolved by welding.

When it comes to keeping your barbecue grill clean, or wrapping food, use aluminum. When it comes to making durable bicycles, use chromoly steel

If you need a much taller frame than you normally find you may want to talk to KOBE:
https://www.bikeforums.net/member.php/77789-KOBE

While I was looking at the Philly Craigslist I saw his Centurion:
https://philadelphia.craigslist.org/bik/2966160446.html

I posted a link to it in C&V and he said he's selling some of his "smaller" bikes.

You accidentally the whole thing.

I am of mixed feelings as to aluminum frames.. I loved the ride of my Klein Quantum. It developed a crack in the top tube after about 12 years. Trek made it right by offering me a 50% warranty. ( Many offer warranties. check out that option.) I swapped a Klein Frame for a 2012 Trek 2.3. At 50% off , it cost me only $480 .
. A reason to have a second bike on hand.. It took the shop almost 3 months to process the claim . Had I not had 3 bikes, I'd been without a bike for that 3 months.

Hi there CycleZealot!

About how many miles did you have on that Klein of yours when the tube cracked?


TIA

I had a aluminum (some sort of named aluminum alloy that is skipping my memory right now) Schwinn racing bike that cracked at the top of the head tube and went down from the headset to about an 1/2 inch. I never hit anything ever with the bike, so how that happened I don't have a clue, I rode if for about 3 years, but after that I swore off aluminum bikes. I also have friends who had problems with their aluminum bikes...but to be honest I have some friends who had theirs for a long time, most notably Cannondale and Klien. Keep in mind, as of 2011 or 12 Cannondale moved their production to China, I would be extremely leery of those.

IMHO, its all about the metals density and environment its kept in... A thin ultralight aluminum product primarily stored outside over a long period of time, maybe even in cold weather... Sure there is a chance it will eventually degrade. Steel stored outside in a damp climate, especially near the ocean, it will degrade. A thin light CF component, same thing.

Everything in existence has a breaking point, and when it occurs is highly conditional. Why do you see more broken aluminum mtbs? Most likely because there are more of them in existence, making them commonplace. A lot of flaming in this chain, and a lot of trolls, but also some very smart replies.

My opinion, keep it... I rock a 97' Proflex 857... Its steel, aluminum, titanium, CF, and plastic... lol and some day it will probably kill me... Most likely when I have a heart attack getting it up a hill...

I'm pretty sure that they're made in Taiwan, not China. Huge difference.

Correct, my mistake; so many big brand bikes are made in China now I forgot that one went to Taiwan.