What's the actual life of an aluminum MTB frame? General answers on the internet state they last at least 6 years because the stress applied to the metal accumulates. However, every so often as I'm watching a bike check video at a bike park, I'll see a rider with a bike much older than that life expectancy. I think the oldest I saw was a fellow riding a 2008 Specialized Big Hit. I also know that Jordan Boostmaster sometimes rides a 2008 Norco A-Line. Is there a key to prolonging the longevity of an aluminum frame? Is it as simple as washing and cleaning the frame on a regular basis? Personally, I was thinking that 6 year mark might be grossly understated for full suspension bike since the shocks should absorb a signification portion of stress? I mean, that's their purpose, correct? Am I way off? Are such older bikes anomalies and not representative of mountain bikes in general? Also, if you don't mind sharing, what's the oldest bike you have that's in good working order?

1973 Masi Gran Criterium ....built under velodromo Vigorelli ....Milan

Depends. Fatigue stresses does accumulate on aluminium, but aluminum bike frames are generally so overbuilt that you can get billions of 'cycles' (one cycle = one excursion from high stress to low stress at any given point on the frame) before failure. But this is assuming the frame is made in such a way, and used in such a way, that no part sees higher stress than the designer anticipated - things like a bad weld, a void in the material, or a very heavy or strong rider, can result in stresses that will fatigue the frame earlier than you'd expect. Also, heavy jumping or crashing or other non-standard applications of stress are more likely to cause non-fatigue failure.

So the rule is, check your bike regularly for any cracks starting to develop, more often if you feel you are putting higher than normal loads on the frame by the way you use it. Especially check spots near welds and suspension pivots.

I am a big guy who rides a lot of miles and I have only ever had one aluminum frame fail, and it was a road-touring frame I did lots of thoughtless off-roading on, and I was riding it for months not knowing there was a crack before I retired it. I replaced it with an identical aluminum frame and have 10s of thousands of kms on the replacement so far, but fewer abusive 'off road' rides than I had done on the original.

My Giant is probably 15 or more years old. Still going strong. Has sat a fair amount but as Clyde stated .... it seems way overbuilt for a entry/mid level hardtail from way back. I would have to be sending jumps way bigger than my broke old self is willing to try to break it I reckon.

Depends on how hard you ride. Mine's over 40 years old and still trucking and I was told to avoid buying carbon fiber because the way I ride I'd break it

Really? Isn't carbon fiber stronger than aluminum, or was that not the case when you bought your bike?

Robbo - I'm no expert but that's what I keep being told. 1/2 the new bike I just bought is carbon fiber so we'll see.

And, a number of years before that bike was built, I raced on a Raleigh Professional, 1964 Tokyo Olympics model, designed by Cino Cinelli. Yes, you and I know what we're talking about, but only one of us believes that either of our posts has any relevance to this topic.

That said, I continue to ride a 1987 Cannondale MT-500 mountain bike, despite having once slammed it into a tree after losing control while riding downhill at speed. Bent the steel fork badly. The aluminum frame is still going strong.

The advantage to aluminum frames, and the reason that they dominate the middle price range, is that it's inexpensive to use aluminum to build a frame with a safety margin of extra material for strength and reliability while maintaining reasonably low weight. I worked in bike stores for over a decade in the '80s and into the '90s and saw .how few warranty replacements of aluminum frames were needed compared to steel frames. I gradually replaced my steel bikes with aluminum bikes, from the early 2000's on. Still own and ride every aluminum bike I've ever bought.

I have two 2008 aluminum mountain bikes in the garage, both of which are used heavily (mine moreso than my wife's). They are both fine, and I rather suspect those frames will outlive us. I'm pretty sure they have a lifetime warranty (Trek), whatever lifetime means. I'm actually kind of anti-aluminum, but I think the failure rate from a quality frame is quite low.

My 2005 Santa Cruz Superlight has been ridden an average of three times a week for almost 17 years, 25,000+ off road miles and exhibits no signs of failure, 6'1", 180 pound rider.

It's a loaded question with too many variables to have an answer.

How much do you weigh?
How many miles do you put on in a year?
How many jumps or drops do you do?
How many Rock Gardens do you ride?

I have a friend that mountain bikes over 5,000 miles per year. He doesn't do jumps or drops but rides rock gardens frequently. It took him 6 years to kill a Specialized aluminum hardtail bike.

It's like asking how long will the brakes last on my car. Guarantee the mail man is replacing brake pads and rotors on his car a few times year in less mileage than most of us put on in a few years before they need to be changed.

It is, it has a nearly infinite fatigue life, but unlike aluminum, carbon is susceptible to cracks and damage from direct impact to the frame. For example, if you crash and lay the frame down sideways and part of the frame smashes against a rock...it may end up cracking. An aluminum frame is better in this regard.

I own 2 carbon bikes and one aluminum bike. I do prefer the ride feel of the carbon plus it's lighter weight.

Say what? I pays peeps to put brakes on my rides !!!!

Yeah. So do I. My days of wrenching on cars is over. Other people need money too ya know.

The reality is that most frames will last essentially indefinitely unless there is some design flaw, in which case any material can fail. And if a frame is going to fail due to design/build flaws in a model, then most will do so less than a few years.

Try to make a frame material decisions based on predicted longevity is a fools errand, IMO.

You aren't understanding what's being inferred by that post. It's not that normal riding would cause it to break, but much more likely that poster is hard on his bikes and crashes regularly. Crash impacts are much different than normal riding stresses and not many people engineer frames that will withstand multiple hard impacts. Normal use, yes...crash damage, no.

Some of them break, some don't. I wouldn't worry about it too much.

Materials/manufacture/production methods/quality, bike use and storage conditions are prolly major factors in the expected lifespan of a bike, mtb.
Anecdotely, My '04 Spec Epic FS and '04 Spec Stumpjumper HT, were both bought by me, used (quite hard usage...) in late 2005. I replaced substantial components, wheels, but the frames were undamaged and aside from minor scrapes, had intact frame condition.
I rode them alot for about 4 yrs, rough terrain, smaller air and drops, maintained them regularly. Rode them much less 2010 thru this past summer. No major crashes, no very difficult terrain.
I've gotten back on them this past summer - very frequently. At a strong level - for a 72 yr old... LOL! I'm breaking much sooner and easier than any of these bikes might.
Because I maintained the 'mechanics', and the suspension components were at a better level, They both ride very well considering their design.
I updated both from 26" to being 27.5/26 mullets (along with some other dimensional tweaks), and found them to have a huge improvement. BUT I've also recognized that a HT is just much less fun riding for a 72 yr old. LOL! The old 26' HT will be sold.
If one maintains a bike, replaces the worn out parts, you'll have a bike at least as good as the original design level, for a long time. Prolly better if you successfully 'mullet' a 26.
I do have recent direct ownership and experience with an almost 'new', better level ALU FS 29r and a Upper Level 27.5r carbon FS - the ALu FS 29r will be sold...
The older Spec Epic Mullet will be kept - a fun bike to ride, and quite nice to have as 'backup' I expect to have both FS bikes be placed with me, in my pyramid.

A search of direct science on the specific topic of Aluminum as relates to MTB frame, did give me one reference I found worth reading.
Material and Design Optimization for an Aluminum Bike Frame

Ride On
Yuri

OP had some good questions. Not all of them are addressed by the Usenet-vintage "aluminum has a fatigue life" canard.

Taking care of things definitely helps. But think more armor than cleaning. A really good thing to do on a mountain bike is cover up the right chainstay, to protect it from the bouncing chain, and use frame protector decals. Mostly mountain bikes are made of thick enough tubing that a gouge can't start a crack but you can choose not to risk it.

The purpose of rear suspension is to keep the bike under control. It allows you to ride faster on worse trail. I don't think anyone would reasonably argue that it makes a bike more durable. It creates more locations where forces are transferred and the leverage is increased and adds moving parts.

Absolutely go with whatever any manufacturer suggests for the life of an alloy frame.

I have a book from 1981 called Bicycling Science which was published in England, it is full of all sorts of engineering data and charts etc.. It gives the characteristics of the different bicycle frame materials including aluminum and steel, and it says that for an aluminum frame to be as strong and reliable as a steel frame, it has to have enough aluminum in it so it will weigh as much as the steel frame. But even if that were the case I would still not trust aluminum because unlike steel it can not bend like steel can, then spring back into shape with no loss of life expectancy. If you bend a piece of aluminum with your hands then bend it back two or three times you can break it in half, but with carbon steel with the right heat-treatment you can bend it back and forth almost infinitely.
I bought a steel-framed mountainbike 25 years ago and still ride it hard, but I have replaced the alloy bars and stem with steel items, and the alloy seat-post is next for replacement with a steel item, or steel reinforcement.

My guess is that aluminum bicycle parts exist partly as marketing tools, and partly because aluminum is easier on the stamping and forging dies than steel is. But according to the engineering, it is 100% possible to make a bicycle out of steel that is just as light and at the same time more reliable than out of aluminum. Also, I weight over 200 pounds, so I am extra wary of the life of bike parts. A lot of things may take me out, but if I can eliminate one variable by going with steel I will do it.

In 1981 that opinion was already 70 years wrong, as proven by all the not-steel airplanes. But maybe that's why Kleins and Cannondales weren't made in England, they had to be from somewhere else so they could be a pound lighter than steel frames

No, you would be wrong still. An old friend of mine went to Yale, then worked directly under the head of the USA's air-force during WWII on many projects including the B-29 bomber, and he oversaw the missions to Japan at the end of the war carrying nukes, then continued as a pilot and advisor to the air-force into the late 50s. A few years before his death he told me he would never go up in an aircraft that had more than so many hours on it because the aluminum had a finite life. Military aircraft do not have to have a long service life, and they get billions of dollars in maintenance and parts replacement. And airliners are constantly phased out and replaced with new models, and also receive very heavy maintenance, and they still crash from failure here and there.

I agree an aluminum bike can give years of service, but depending on the weight of the rider and the severity of service, it's life will vary, and it will never be as strong as steel pound-for pound. You can look up the engineering data in hundreds of places, if you think you can understand it.....

MTBs are not airplanes.

One can armchair analize the material science and make speculative predictions….. or one can just look at the real world track records of Al frames in various MTB applications over the past few decades.

The main limitation of steel (which I prefer) vs. aluminum is that it makes it much more difficult to build a full-suspension mountain bike frame.

Here's my Trek 6000, bought in the year 2000, with many thousands of miles on it under a rider a bit over 200 pounds. Frame has held up well.

22-year-old Trek 6000