I was just curious about what are the advantages and disadvantages of the different frame materials on the market. I.E. Chromoly, 6061, 7005 Aluminium, Titanium and Carbon are at the top of my mind. Two points of my interest also would be how Titanium caompare to aluminium and also the differences between 6061 and 7005 aluminium. many prople say that 6061 aluminium is better but then again alot of the top end, exotic frames seem to be made of 7005 series aluminium. This confuses me!!!!

don't forget bamboo

Chromoly is strong yet flexible, allowing it to take rough riding while actually taking a little bit of the edge out of the bumps (some road riders really like that feature). Unlike aluminum or carbon fiber, it is typically not susceptible to fatigue failure. It is heavier than the other options and slightly susceptible to corrosion on exposed metal. Can be welded.

AL 6061 is a general purpose structural aluminum used for it's low cost. It can theoretically save weight over steel for the same strength frame, but is susceptible to fatigue, and usually used in lower quality frames.

7000 series aluminums (7005, 7051, 7075, etc) are high strength aluminum alloys that can save decent amounts of weight over steel for a reasonable cost. Must be heat treated to achieve maximum strength, so it shouldn't be welded after leaving the factory. Probably the most common material of choice due a good balance of properties. More expensive frames may also use 8000 or 9000 series.

Titanium is very strong and lighter than steel, does not corrode, and typically does not fatigue. It is very expensive, both due to the cost of producing it and of forming, machining, and welding it. Can absorb minor bumps like steel, but some riders have complained about the frames being too "flexy."

Carbon fiber is extremely light for its strength and can be formed into unique shapes, but is also expensive. It is somewhat susceptible to fatigue, but becomes drastically more so when scratched, so it's used more in road bikes than mountain bikes. Carbon fiber frames can not effectively repaired.

Thanx, Iamlucky13, very informative. I also did a search on frame materials and found this link in the singlespeed forum.

https://www.sheldonbrown.com/frame-materials.html

Wow... very informative. Thanks. I learned a lot today. Didn't know about the 8 and 9 series.....

Yea, I've been on the eternal search for the strongest frame material for some time now and it just frustrates me, lol. I've come to realize there is no "perfect, never ever worry again" frame out there that I've yet heard of. To each it's own, they all have some flaw.

But I've recently seen in one of my mtb magz that independant fabrication is coming out with "Mar-aging Reynolds 953 Ultra High Strength Steel" frame on a new bmx/dirtjump style bike. Says it's supposed to be as tough as titanium and somewhat less corrosive than recent steels.

Can anyone shed a little more light on the 953?

The more i read about aluminium, the more im thinking that chromoly is a superior material to make frames out of as long as weight isnt a huge factor.

Would i be correct in assuming that a chromoly frame is better than a 6061 frame? Even if it is a little heavier?

A question if i may?

This is what Iron Horse said about the 2006 Warrior Expert frame -

DOUBLE BUTTED ALLOY HARDTAIL FRAME

Am i correct in assuming that thats a chromoly frame? Or is that aluminium? I would have thought they would have specifically said aluminium if it was?

It's aluminum. Somehow "alloy" has become short for "aluminum alloy" in cycling and sports equipment. Yes, steel is by definition an alloy and titanium usually is alloyed, but ignore that . Also, from Iron Horse's website about the Warrior Expert (probably the 2005 though, I have no idea if they've updated their website yet):

The "6061" designation is a specific aluminum alloy (see here for more information).

You'll also see nomenclature with aluminium relating to the hardness. "6061-T6" where the "T6" indicates hardness on (I believe) the Rockwell B scale

And the engineers here can speak to this more clearly than I, but the myriad of aluminium "blends" often relate to tradeoffs in strength vs. workability. I remember reading one of the 70** series alloys is pretty strong but doesn't weld easily or well, hence it's used a lot for chainrings and other parts that can be stamped, etc.

Carbon Fibre always fascinates me in that it's so strong and light yet so vulnerable to catastrophic failure resulting from a relatively minor ding or scratch. Auto racing fans might remember some spectacular wrecks, especially in the late 80's early 90's when engineers were still figuring out the best way to align the sheets for impact protection. I'm still haunted by those pictures from F1 driver Martin Donnelly's 1990 career-ending shunt during practice for the Spanish Grand Prix at Jerez.

Thanks for the info guys.

OS titanium is your friend.

I think you're confusing fatigue for notch-sensitivity. Most CF in fact have very high fatigue strength and fatigue life and some like steel do not exhibit a fatigue limit. There are various forms of CF. Some can be repaired (thermoplastics) and some cannot. Still, it's generally accepted that CF repair is not a viable option on a bike frame. I know of some people who have repaired their thermo-CF frames but it's really not for the faint-of-heart and you should definately know what you're doing. I should also add that the use of thermoplastics in bike frames is pretty rare. I believe only three manufacturers ever did it (GT, K2 and Mantis) and I do not know of any current thermoplastic CF frames in production.

The "T" designation in aluminum deals with the way that the alloy was tempered. Gobs of Aluminum Info This site just about tells you anything you want to know about aluminum.

Carbon Fibre frames are as strong as the lay of the threads. Carbon fibre is laid in well..... layers Between each layer is a resin, by changin gthe angle of the layers and the direction the threads run you can, quite easily make a tube stronger and much lighter than the equivalent Aluminium tube. It is also possible to build in certain flex characteristics, but CF is not known for its ability to flex much...... it will flex a tiny bit, but unlike AL or Chromo it won't bend, it will shatter. Also by adjusting the lay pattern you could make a tube super strong on the X axis but weaker on the Y axis, etc etc etc.

Be careful with generalisations. CF can be engineered to flex. The beampost on this Softride has quite a bit of flex in it...

Interesting, I didn't know that anyone had made frames with thermoplastic binder, because hard-setting polymers can make (as far as I know) the strongest composites. Currently, repairing a CF frame is not feasible and it's doubtful that it ever would be as feasible as say, fixing a steel frame, especially if the weave gets messed up.

Notch-sensitivity has a significant effect on fatigue life because notches create a stress concentration and because fatigue life is logarithmic with stress, deep scratches in the wrong palce can exponentially decrease life.


I hadn't heard of it, but that doesn't mean it doesn't exist. It's probably not terribly different from Reynolds 853 (or maybe you mistook the number). 853 is a steel alloy made by Reynolds that I believe is nearly identical to AISI 4130 (a common chromoly): very high strength, hard, good corrosion resitance, decent weldability.


To add to what Khuon said, there's a few soft tail mountain bikes that have 1-2" of rear travel by flexing the carbon fiber chain-stays.

Here is the scoop on the 953 tubing. Reynolds 953 It turns out that is is a stainless steel, which would lead me to believe that it is actually not as strong as a chromoly steel.

Iamlucky13.

Next time you're in the bookstore (assuming you frequently visit one) check out the new Mountain Biking Magazine January 2006 Volume 20/Number 1 Page 31. It very clearly prints reynolds 953.

Check it out if you get the chance.

Mmmkay?!

Most materials have fatigue/yield strengths specified in both notched and unnotched. Yes, it's true that notches/scratches in CF can affect fatigue strength and fatigue life but it's not right to say that CF has a lower fatigue strength because of it. To give a similar analogy to metals, it would be like saying that steel has a low fatigue strength due to hydrogen embrittlement. The downside to CF is in fact notch-sensitivity and not low fatigue strength.

Thermoplastics have a lower strength to weight ratio. They have a lower compactness. They however are less succeptable to abrasion and notch-failures than thermosets. They are also more ductile and can be "recycled", patched and repaired. But as you say (and as I've said before), it's not an easy task. Richard Cunningham (Mantis) teamed together with GT back in the mid-1990s to produce a thermoplastic bike. Not all of the bike was CF however... only the main triangle. GT later went on to make a full thermoplastic frame. Mantis also produced a full thermoplastic frame called the Screaming V. A year later, K2/Pro-Flex introduced the 4500C/5500C/Oz frames which were also full thermoplastic. And I forgot one company in my initial post on the subject. Cannondale also produced the thermoplastic Raven. The Screaming V, K2 Oz and Cannondale Raven shared some common features... primarily in construction where the main frame was produced using two shell halves bonded to a central spine. In the Mantis and K2 bikes, this spine was made of CF. In the Cannondale bike, this was initially made of aluminum and then later on magnesium. Both K2 and Cannondale had been playing thermoplastics before releasing a full frame. In the case of K2, they used thermoplastic construction for some of their forks (Girvin).

Good point. Thanks for clarifying and for info on the thermoplastic frames. I admit I don't work with CF a lot, so there's a lot of remembering back to materials science sophomore year.

Agree, disagree? Anyone?

What an informative thread this is turning out to be...wow!

Wouldn't Reynolds have recommendations for the application(s) that it would be appropriate for? That's one company (of only a handful) whose word I would be willing to trust.

The tensile strength of steel can vary depending on the grade of material and the heat treatment. Most comparisons with titanium only look at the cheap versions of chromoly but heat-treated versions can have 2-3x the strength so can be fabricated into thinner-walled tubesets. The desnity of steel is all the same so high end tubesets are lighter.
953 is a close relation to Airmet100, the strongest metal ever to be made into a tube. It was developed for the undercarriage of carrier-landing aircraft. A few bikes were made on Airmet100 but it was a very tough material to work with.