Bike Frame Buying,
Building, Metallurgy and Tubing
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Frame Builders | Best frame material | Steel vs Aluminum | Check for wear | Choosing a tube set | Tubing manufacturers
Here are a couple sources of information and commentaries on bicycle frame building and metallurgy related to bicycle frame tubing.
(1) Bibiliography: Bicycle: Repair, Maintenance and Building. Several books pertaining to designing and building bikes are included. Unfortunately most are not easy to find.
(2) The page Bicycle Science, Engineering and Technology
(3) Frame builders archives:
http://www.thebicyclestory.com/category/frame-builders/
(4) What is the best material for a bike frame?
There is no absolute answer. It boils done to the engineering of the fame and the personal preference of the user. By choosing different tubing (tube diameter and wall thickness) and frame geometry, a skilled frame builder can make a soft or stiff frame out of steel, aluminum or alloy. It is not so much a matter of the material, but how it is used that determines the ride characteristics of a bicycle. It is a mystery what determines every individual riders personal preference. For articles on choosing a material search for "metallurgy" and "buying bikes" in the archives of the Adventure Cycling magazine on their web site: http://www.adv-cycling.org . Many of these articles were written by John Schubert, Technical Editor, Adventure Cyclist Magazine. Here is a sample of his insight, specifically touring bike frames:
Out of steel, aluminum, titanium and carbon fiber frames, my favorites are steel and aluminum, but intellectual honesty demands that I point out that other well-informed people will have different preferences. My reasoning: Carbon fiber needs to be babied -- cleaned after every ride, stored in a nice place, washed and waxed from time to time, and protected from even the slightest abuse, which is inconsistent with most touring. A good steel bike offers a great ride. Aluminum can be (and these days it customarily is) designed to be lighter and stiffer than steel.
However, these properties (strength and stiffness) depend on the entire bike design. The material selection is only the beginning.
Metal matrix allows some improvements in the bulk properties of aluminum that mere alloying cannot achieve. It's on the order of magnitude of 10 percent improvement in stiffness and/or strength.
Some manufacturers have embraced metal matrix. Others haven't bothered, saying it's not worth the bother to get that fairly small improvement over aluminum (which basically has terrific bulk properties for bicycle frame design).
Since I at least try to speak with scientific rigor, and not throw out slapshot opinions: Whether metal matrix in general, or "X" design in particular, translates into an improved bike frame, and how that would compare with other good bike frames of other materials, would be a good topic for a master's thesis. However, no one who is interested has the combination of time, money and skills to do the complex research required to really answer the question.
You won't find any meaningful published test data to compare different frames. The commercial magazines have all descended into the "like wow dude" level of un-sophistication in road tests, and aren't about to get serious. Adventure Cyclist has neither the money nor the inclination to try. Manufacturers' literature is usually skimpy and occasionally inaccurate, because their goal is to sell, not to write a thesis."
I'm not as enthralled with titanium because it's an expensive way to get a bike slightly lighter and not as stiff as an aluminum bike. And frankly, I haven't kept up with the latest carbon fiber designs enough to have a well informed opinion.
Getting back to various steel bikes, if all the frame dimensions were the same, the metallurgical differences would be invisible to you as a rider. Every kind of steel "feels" the same to the rider with two caveats:
Better steels are stronger (more crashworthy), and hence they allow the bike designer to use thinner-wall tubing to save weight. This also makes the bike less stiff. So yes, the most expensive steel bike will not be as rigid as a lesser-priced steel bike. However, the differences are minor.
A saying among people who write road test articles is "My favorite bike is the one I just finished riding." Whatever the differences are, they're small enough that one can fall in love with any of them.
Comfort differences among road frames are tiny, because every road frame is a rigid truss structure that has very little "give" in the vertical plane.
The best way for you to ensure your comfort is to get a bike that accepts larger tires. The air volume of good-size tires absorbs far, far more road shock than the tiny differences among frame materials. To get this kind of bike, insist on a touring bike that will accept tires at least as large as 700x32C, or preferably 700x35C. If you get such a bike, you can always put skinny tires on it -- in which case it will handle just about identically to a racing bike (which couldn't accept the more comfortable touring tires).
Not all bike shops stock touring bikes, and some would be unwilling to order them for you, but such bikes are made by Trek, Cannondale, Jamis, Raleigh, Bianchi and numerous smaller companies. Don't let someone sell you a "racing bike with three chainwheels," though -- such bikes, which are more common in the bike business, can't accept the larger-diameter tires and therefore won't have the comfort for touring."
(5) Steel vs. Aluminum for chopper bikes / art bikes: Chalo, a long time custom bike builder and friend of IBF, gives the following advice:
For amateur chopper construction, steel is a much better material than aluminum for several reasons.
Steel can be welded without significant loss of strength. Aluminum requires expensive heat treatment to restore its strength after welding.
The equipment and inert gases required to weld aluminum are much more expensive and elaborate than necessary for steel.
Steel can be brazed with brass, silver, nickel-copper, or other filler alloys. Aluminum cannot be brazed in the conventional sense. There are aluminum solders, but they are too weak to be useful for bicycles.
Steel can be drilled and bolted without unusual risk of cracks propagating from the drilled holes. Aluminum will often generate cracks starting at holes drilled in stress areas.
Steel can be formed (bent) to a greater degree before significant strength is lost, compared to aluminum which only forms well in its annealed (soft and weak) state.
When a chopper's design is insufficient to cope with the loads imposed upon it, steel is more likely to bend rather than break off completely when it fails.
Add to all these reasons the much lower cost of steel bike frames and raw materials of any given quality, and it's pretty easy to see that steel is a better material for chopper building than aluminum in most circumstances. A few exceptions to this general principle are as follows:
Parts machined from solid blocks are better made from aluminum, because it is lighter and easier to cut.
When a commercial bike frame is to be used without modification, and when the parts attached to it do not add unusual stresses above those expected from normal use, then an aluminum frame may be used.
When very fat tubes and parts are desired which would be too heavy if made from steel, aluminum may be used. The rule of thumb is that you should use at least the same weight of aluminum that you would steel, about 3 times more volume than a comparable steel part.
(6) Do frames fatigue, wear out and fail?
As you might imagine, frames vary tremendously. So many millions of frames have been built, in so many thousands of designs, that some are going to be more failure-prone than others.
To generalize, aluminum is fussier than steel. Aluminum has a finite fatigue life; steel doesn't. That's what the textbooks say. But some steel frames manage to crack too.
Similarly, titanium is supposed to be just about crack-proof, but there are exceptions to that too. And carbon fiber's structural integrity depends heavily on the quality of the design and workmanship.
An aluminum frame subject to repeated heavy loading (being bashed in hard mountain bike use) may last a few years. At the other extreme, an aluminum frame that is not stressed (ridden gently on the smooth road) may last for decades.
At appropriate intervals all frames should be inspected from nose to toes for small cracks. Small cracks grow; they never shrink. So when you see one, take it to your dealer, who will probably tell you the frame is toast.
Cannondale Bicycle Corporation has posted a discussion of this topic in their online Owner's Manuel, http://www.cannondale.com/Asset/iu_files/116376.pdf. Go to section D, "Inspection for Safety" and take particular note of "Fatigue 101," in Part II.
Gary Klein discusses some quality issues of aluminum frames starting on page 5 of the PDF document at http://www.kleinjapan.com/at_klein/garys_speech.pdf
"Aluminum Time Bomb" in the May 1995 issue of Mountain Bike Action magazine also address this issue.
(7) How do you choose an aluminum tube set?
Despite what the advertising tells you, the specific alloy of aluminum used is one of the least important factors in determining ride characteristics.
All alloys of aluminum have identical weight and stiffness. Where the various alloys differ is in their yield strength (which determines crashworthiness, not ride qualities), resistance to fatigue, and stuff that affects manufacturing processes (how to weld, how/whether to heat treat, etc.) This is largely academic for the end user because all high end bikes will be designed to have acceptable crashworthiness and fatigue qualities.
The physical dimensions of the frame -- tube diameter and wall thickness -- determine the ride quality, which is the factor I would base my buying decision on. However, there is no way to tease that information out of the sparse information the manufacturers provide. They generally don't publicize enough information to plug into the finite element analysis program that would be necessary to even try to calculate this.
So we're back to test rides. Find a shop that allows good test rides, do an A-B comparison, with the tires pumped to identical pressure. And if you find you have trouble telling the difference, don't be surprised. The differences in riding qualities among many, many, many bikes are so minute that you might as well pick the paint job you like the most.
John Schubert, Technical Editor, Adventure Cyclist Magazine
(8) Bicycle tubing manufactures:
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