steel vs aluminum

I know this has been done to death, and i’m not trying to start one, but i’m in the middle of a really annoying argument with someone about how steel has better dampening properties than aluminum. Everyone in the bicycle industry takes this as common sense, but when asked for factual data, I can’t come up with any. Do you guys have links to sites or test reports comparing the dampening properties of steel and aluminum?

Sorry man, I think this is mostly just folklore.

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

All I know is that geometry plays more of a role in how “smooth” a bike rides than tubing material. I have ridden VERY harsh NJS frames and very smooth aluminum frames. I think tire selection makes more difference than frame material. If you put some nice 32 hole tubulars (or even a high quality clincher like an Open Corsa) hand it will make any bike ride smooth.

Surely how you set up your bike and the geometry of the bicycle has much to do with how it will ride, but i’m talking about the material itself. I have heard from two different engineers, one that worked for American Classic, the other at Giant, they have both told me about dampening properties of carbon fiber and aluminum, and how carbon fiber as a material itself is much better at dampening than aluminum ever could. Therefore when they designing a bicycle, they design the bike with the material in mind so the design can overcome any weakness that the material has. So yes, i agree to a certain extent what Sheldon is saying, but on the same note the materials still have properties of its own. The idea that all materials are equal just isnt’ true. You just can’t form steel and aluminum into space age flying machines like you can carbon. Therefore the potential for aerodynamics on a carbon frame is always going to be much higher than steel or aluminum.
I’m not questioning so much about ride quality (tho ultimately that is what is important) but more about the material’s property .

as far as the aerodynamics of carbon compared to aluminum frames:
whats it matter? everyone builds frames so similarly, any frame built out of carbon that is available to the public could just as easily be built out of aluminum

and a side note*
i was always under the impression that dampening meant to make something slightly wet
and damping was a material’s physical property to flex

[quote=GRHebard]
i was always under the impression that dampening meant to make something slightly wet
and damping was a material’s physical property to flex[/quote]

yes, thanks for that.

[quote=GRHebard]as far as the aerodynamics of carbon compared to aluminum frames:
whats it matter? everyone builds frames so similarly, any frame built out of carbon that is available to the public could just as easily be built out of aluminum.
[/quote]

Generally speaking yes, but not when you get to those 4-5 thousand dollars tt machines. Aluminum and steel still comes out as tubes you have to form while carbon is like playing with paper mache.

Steel is real, dawg.

Carbon fiber can be engineered into a shape that oscillates like a spring. In many ways, forks are like this. Carbon fiber, like steel, can be engineered to have a longer fatigue life than aluminum under these conditions. So, in this sense, carbon fiber can be said to have damping qualities where aluminum doesn’t.

another neat fact is that, unlike wood and other materials, carbon fiber doesnt become more flexy over time.

tl;dr, but:

i was under the impression that the size and shape of tubing plays a big role in how forgiving a frame was. larger tubes = stiffer frame, regardless of material.

i would like steel 42mm rims please

A round hollow tube with a large diameter will be less flexible than a round hollow tube of a smaller diameter, keeping length and even weight constant (You can thank Mr. Wizard on Nickelodeon for that bit of knowledge). Within reason obviously. Make the tube too large and the walls become too thin and you’re riding a soda can. This means that if two frames were the same weight and of the exact same design/geometry, the one with the larger diameter tubes would be stiffer. This doesn’t, however, give any information on the transference of high frequency vibrations. It seems logical that a stiffer bike would be poor at damping vibration, but I don’t think that is always the case.

my road bike is aluminum and my tarck is steel. i don’t notice a thing.

Geez… is everyone here an art student?

Alu is weaker than steel. To make alu frames strong, they used larger dimension tubes - bending resistance is proportional to the cube of the depth of a rectangular section, and I’ve forgotten what it is for a circle but it increases geometrically with the diameter. So alu bikes (except the early ones which just used thicker wall tubing of about the same diameter) are typically stiffer. BUT you can design them whatever way you want. The beauty of CF is that you can make it thick where it needs to be thick and thinner where it doesn’t and deep in section where you want stiffness. Bike makers are now hydroforming alu frames so you can get different geometry along the tube to make is stronger where it needs to be.

But in the end steel is real. Alu frames fatigue over time. No getting around it. Steel if you keep it under the limit will bounce back indefinitely. Steel is also tough and won’t fracture like carbon. The resins which bond the carbon fiber are probably good shit, but I have to believe that UV light will eventually degrade them and they will fail like the plastic patio chair I broke this weekend.

If you want a bike to last 30 years, steel is your best choice.

havent we been debating steel/alum/CF in like 3 or 4 different threads lately

Composites are commonly know as FRP or fiber-reinforced plastic, which is what people are referring to when they use the term “carbon fiber”. Plastic has a bad habit of decomposing when exposed to ultraviolet light. Thus the comparison of plastic lawn furniture to CF bits.

My response was more relevant prior to an earlier edit above.

Steel has an infinite fatigue life if the part never exceeds yield. Aluminum has a finite fatigue life. Sometimes that finite period of time is well in excess of the useful life of the part.

That’s great, but it’s also orthogonal to the point of the OP which specifically asks about the damping characteristics of the various materials. I’m not an art student, but I’m also not a mechanical engineer. If you wouldn’t mind obliging us, I’d like to see a short dissertation on the topic.

As much as I respect what you say, this is simply not true. Yield strength is defined by the situation when the piece under load is deformed permanently. This is lowered long term if the piece is subject to cyclic load still in elastic regime i.e. under yield stress which is defining the end limit of the elastic regime, and the lifespan of the part subject to such loads expressed in the number of load cycles is called fatigue life - it is a function of the amplitude of the periodic loads.

For steel (and titanium) there exist a threshold of these cyclic loads below which the fatigue life is infinite. For aluminum, there is no such threshold and I guess this is something you are referring to.

Bikes are not designed taking this threshold as a nominal load - they would come out too heavy. For longevity it pays to use the bike built for stronger rider than you.

I probably have more art major than anyone on this board.

Say that to the bottom bracket on my '98 Trek 5200.

Also, IMO, those testing results aren’t published because they are scary and will hurt sales. I dented my Ttube when it tipped on to a soft and cushy couch. seriously wtf!!! Still, it doesn’t rust and I’m tired of rusted out bb shells.