State of the Art

State of the Art

When I think back on some of the products I used to use and just how colossally, phenomenally slow they were from an aero standpoint, I’m amazed that I was able to ride at the speeds I did. One helmet I used to wear—no names mentioned, but it was very popular in the late 1990s—an engineer once described to me as a foam wind sock. Well, those are my words, but that’s a fair characterization of how he dismissed it. Those gigantic, tubular, carbon fiber spokes found on some wheels? The least aerodynamic wheels since … well, since the invention of the steel, J-bend spoke, which is almost like saying since pretty much ever. Some of those allegedly aero-shaped aluminum frames were actually slower than regular round-tube steel.

Freeing up money for engineers to visit wind tunnels made a big difference in the aero products the bike industry produced. However, the time was so expensive that initially companies rarely made a trip to the wind tunnel until they actually had not just a working prototype, but often a production sample. In other words, the trip to the wind tunnel was often just a matter of find out how fast a product was—or was not. The vagaries of the English language accommodated bad news at the wind tunnel. You could honestly say, “wind tunnel tested” in your marketing copy, and that was technically true. It didn’t mean the company in question had actually used the wind tunnel for development, as in changing a design based on feedback from the results of a series of blows. And because of the locations of most of the wind tunnels available to the bike industry through the 1990s, development didn’t permit multiple trips. So they’d do one at the end. Boom. Tested.


Things didn’t really begin to change until companies started to invest in computational fluid dynamics analysis. Initially, most companies outsourced the analysis to engineering consultancies. Later, they spent the big bucks on high-powered work stations running the software. Better known as CFD for short, this software allows engineers to break down a bicycle into tiny components, like a fork or a down tube, and play with shapes and then see just what is faster. It’s an infinitely better system of learning just what’s going on with a shape than adding clay to a fork to see if that makes the air less turbulent.

Zipp was the first company I encountered to actually purchase a license for any CFD software. Since then, plenty of companies have stepped up to use the software. While most manufacturers I’ve talked to are a bit reticent to talk about how they choose to work, I’ve been able to find out that CD-adapco’s Star CCM+ is probably the most commonly used software. The software is crazy expensive—an annual license runs what a low-end Beemer does—and requires multicore processing to the tune of at least eight processors, but preferably 16 or 32.

Once an engineer has defined a shape, say for a down tube, they’ll write a script that asks the software to simulate a series of blows, such as at 0, 5, 10, 15 and 20 degrees. And then they hit “run” and leave for the night. If the workstation is powerful enough, they’ll have results the next morning. If they are running a portion of a frame, say the front triangle, a three-day weekend is handy.

As aerodynamic shapes have improved to better Judo the wind, engineers have begun to address a competing requirement. While you can make a bike that is narrower than a butcher knife, it’ll be as pleasant to ride as the Northridge earthquake. So the smart companies have begun to address a rider’s need for comfort, not to mention the larger need for control; if a bike is too stiff vertically, the rear wheel will bounce into the air over even moderate pavement cracks. Any time a wheel isn’t in contact with the road, that’s a loss in control. There’s also the need for a bike to retain enough torsional stiffness to allow a rider to sprint without having to temper that effort due to a vague-handling front end.

IMG_6838This frame’s front derailleur mount was drilled twice, once incorrectly, and then once in the right place. Note how uneven the wall thicknesses can be at the edges. 


Wrap it
For all the noise bike companies make about the carbon fiber they use, they tend to keep close counsel on just how they lay that carbon fiber up. Based on what I’ve learned, I’d rather ride a bike that used all 30 ton fiber and was laid up using the latest technology than one in which a sophisticated mix of 30, 60 and 120-ton fibers available were wrapped around a bladder and stuffed into a mold, circa 2005.

And at last, for the most part, we have the industry talking the same language when it comes to fibers. When they used to refer to intermediate modulus, they were talking about 30-ton fiber. High modulus was 60-ton fiber and ultra-high modulus was 120-ton fiber.

To make a great carbon fiber frame, a manufacturer must do three things. They must first create a blend of 30, 60 and 120-ton fibers to create a frame that will be stiff, lively and yet strong enough to survive hitting a speed bump at 25 mph without shattering like a frozen carnation. Second, they must create a layup schedule that utilizes these fibers in exactly the right places so that the frame can accomplish the aforementioned goals and still weigh less than a kilogram—which remains an issue for many manufacturers. Finally, they need to provide a structure on which to lay up these fibers so that they are placed in the precise locations specified in the layup schedule. A little twist in a bladder could see those 9-o’clock and 3-o’clock ribs shifted to 6 o’clock and 12 o’clock, suddenly stealing lateral stiffness and making a frame more vertically stiff.

Oh joy.

Bike companies really don’t like to talk too much about this part of their operation, but this is the part of carbon fiber technology use in bike frames that has been transformed most radically over the last 10 years. The first layup schedules I saw in 2005 were four or five pages. Four dozen steps or so, and those were wildly sophisticated relative to the mandril-wrapped tubes of the 1990s. You get ten to twelve steps per page and while today each step is an individual piece of carbon fiber laid down, back then, a layup schedule could specify multiple sheets oriented the same way in the same position. The layup step will detail what the size and shape of the piece of carbon is, where it is to be placed and in what orientation. Imagine a three-dimensional jigsaw puzzle that can only be put together if you do it in the right order. Without the layup schedule, you’d need to be a Mensa member just to produce a result that looked like a bike but was unrideable.

The layup schedule for one current, super-coveted (and super-expensive) road bike is a bit more than 250 steps, by my rough estimate. By comparison, Felt’s top-of-the-line aero road bike, the AR FRD, has a layup schedule detailing more than 300 individual layup steps.

IMG_6839Not only are the wall thicknesses wildly variable on this frame, you can see where the work was performed hastily and material got bunched up in places. 

Let’s talk about steel for a second. Large-scale production of lugged steel frames demanded that builders braze with brass. The tubes could be heated up on a carousel by large torches and workers could simply feed brass rod like pushing cotton candy into your mouth. Because of the high temperatures used in brass brazing, the joint didn’t need to be particularly clean; any imperfections would burn up in the brazing. You didn’t need an especially skilled workforce to produce brass-brazed frames by the bushel, just some guys to make sure they were straight upon completion. However, because they were heated until the tubes and lugs glowed red (framebuilders like to call them “rose buds”), the heat treating was compromised, which is why every guy I knew in the ’80s and ’90s who rode a Colnago had it break at either the drive-side dropout or the drive-side chainstay at the bottom bracket.

So when a builder touted that his bikes were silver brazed, it was shorthand for a couple of details. First, it meant that he cleaned each tube and lug prior to brazing to make sure the silver joint would hold. It also meant that the frame would last longer because the heat treating hadn’t been ruined in a carousel. Finally, it meant that the extra care required in building was time-consuming and would prevent him from building 600 frames in a year.

So it is with carbon fiber.

The more steps in the layup, the more different pieces of carbon fiber used, the more care that must exercised in laying up a frame. More steps, more care means more time means fewer employees skilled enough to do the work means fewer frames laid up in a day. That drives up cost and down availability. That’s why it’s one thing to want to buy a Cervelo Rca, but another thing for your shop to locate one you can buy.

From what I’ve been able to find out from a few companies, those most coveted frames, the ones in short supply often take a full day to lay up. While that may sound really quick, given that many builders working in steel may need three days to produce a frame, try to remember, that one day is just layup. That doesn’t take into account all the finite element analysis (FEA) and CFD done on the front end, all the work done on designing the layup and then plotting the layout and cuts of each piece of carbon fiber. Put another way, layup is roughly comparable to brazing in steel terms. A fair comparison would be to equate it to a builder being handed a complete set of tubes that have been coped, lugs that have been prepped and filed and a jig set up. With all that in place, many builders could produce a frame in a day.

IMG_9044At the upper end of the market, some manufacturers have begun to move to sophisticated shapes to help form the carbon fiber instead of a loose bladder. Compaction—and frame strength—has improved dramatically.



I’m seeing two basic approaches to tooling in the bigger companies. The first is to take the tooling that was formerly used for the priciest bikes and move it down line so that those molds are used to produce the less expensive frames. The layup schedule gets simplified and more sheets of 30 ton fiber get used to produce a frame that’s roughly as stiff as the top-shelf bike, but at a greater weight and with a less lively ride.

The other approach is to purchase boatloads of tooling—enough to produce all of your frames for a model year—when you come out with a new frame and then just change the layup schedule depending on which price point is being built.

I’ve heard arguments for both approaches, but I have my suspicions that this is one of those decisions that may sometimes be made by the CFO and not the head of engineering. I can totally see number crunchers saying, “But see how much we save if we can get two more seasons out of this tooling.”

That covers what happens outside of the frame. And for the most part, frames are still being laid up without the aid of any significant internal structure. The big change is at the high end, of course. We’re starting to see structures that provide exact tolerances for internal shapes. This does two things: first, it helps eliminate any problems in compaction in difficult shapes and it also gives the person performing layup a better structure on which to place the carbon, for greater precision in layup. The increasing use of inner molds on which to set the carbon is what’s leading the way in the arms race decrease frame weight by companies like Guru, Cervelo, BH and others.

In your garage
It’s fair to observe that in the early days of carbon fiber manufacturers chased weight savings before they really knew what they were doing. Most of the ’90s and aughts were marked by frames that were more likely to be sent back under warranty conditions than not. The exceptions were produced by companies that talked more about stiffness and less about weight. As companies have increased their spend on both engineers and resources for them, the frames have gotten markedly better, and are much less likely to suffer a non-catastrophic failure that will result in a warranty return.

Ultimately, the question riders face is what they want hanging in the garage. There are plenty of riders who either never moved to carbon fiber or haven’t purchased a new bike in the last three or more years. The landscape has changed radically. Even if you’re not in the market for a new bike, if your local shop sponsors a demo day with one of their lines, it’s worth you time just to go give one of the new generation of bikes a try. The experience will remind you of why you started liking bikes in the first place.


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  1. Andrew

    Oddly enough, as all this great work is being done in carbon, I’m replacing my carbon frame with a Hampsten La Dolce Vita steel frame.

    1. Author

      Andrew: There’s definitely been a resurgence in steel and titanium. With good reason. Enjoy your new bike. Steve does great work.

  2. JohnK

    Great informative and even-handed piece. I ride steel myself for the feel, the craftsmanship, and the unique experience of being able to work personally with the builder. (I also hate when mom dresses us alike.) That said, I do love tech, and it is really interesting to see the progress that has been made with carbon frames and the labor and effort that goes into building one. From the personal, subjective side, I think of a bike as a major purchase, something I hope to get at least ten years out of, and my hesitancy to jump into carbon has something to do with the speed of this progress, that two years after I buy my carbon dream machine the new one comes out that makes me think I should have waited.

    1. Author

      JohnK: I think it used to be smart to replace a carbon bike after five years just for safety reasons. My suspicion is that today’s bikes are far more likely to last 10 years as serviceable machines. That said, the way the technology is improving, it will probably make sense to sell your rig after three years and put that money into a new bike. Flipping a bike the way you might flip a car doesn’t always make the best economic sense, but we’re not in cycling for financial stability, are we?

  3. Andrew

    It’s a pity that you can’t lease bikes, the way you can lease cars. I’ve always leased, because it’s a way to try new things out. I’d lease one of the sexy new aero carbon bikes in a heartbeat, even though I’m buying steel!!

  4. Some guy up in the Oregon Gorge

    I picked up a plastic fantastic carbon frame back in the mid 90’s from a notably “artful” framebuilder in Southern Oregon who was tired of seeing the carbon freak hanging around in his shop…… Apparently it had emigrated from some Asian framebuilder that was looking to get in on the carbon frame market. It’s not the lightest thing around nor is it the stiffest, but after 50 or so thousand kilometers, it hasn’t collapsed on me yet……. I’m a reliability kind of rider and like to ride my bikes into the ground. When I pick up a new frame, I’m going to look for one that is similar to the one I have that has bit more heft and a little less svelt, so that I can be assured of many miles on it……. Besides, I’m a fast old man (at least in my mind) and I don’t need no steenking feather bike to kick butt and ascend like Alberto C……..

    Oh yeah ! Good article !

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