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Carbon Frames

by Bill McCready

(Carbon-Rahmen für Tandems - und ein wenig Werbung. Aufbereitet aus der englischsprachigen Mailingliste, 10/2003)

Mark Livingood has posted a couple of notes about Santana's new carbon tandems.

"According to my source," Mark reports "it was pretty much built by Titus."

Bills response: The "mystery" dual suspension carbon tandem Mark refers to was spotted and photographed at Interbike while sitting in the Titus booth. Because it also had a Titus rear suspension, some confusion is understandable. The tandem itself, however, was designed and built at Santana. Like its namesake (Santana's '98-'01 Dual Moto) and unlike every other dual-suspension tandem we've tested, this bike climbs as capably as it descends. Because we're still working on a new fork, the world's first dual-suspension carbon tandem is still a few months from production. Weight: under 40 pounds.

Livingood again: "I would ... note that similar titanium & carbon [single bike] framesets from Merlin and Serotta ..."

My response: While frames from other builders may appear similar, the frame technology of Santana's carbon tandems is entirely different in a number of ways.

The following post will help to demystify carbon. Again, because the tightly-written explanations will defy a quick skim, it's best to print it now and study it at your leisure.

In order to understand some distinctions between the Beyond and frames that appear similar, here are nine salient differences

First, in the process of being pressure-cured, carbon fiber tubing gets a controlled (smooth) side formed against an impermeable mandrel or mold, and an uncontrolled (uneven) side that results when gasses and voids are flushed out. With the standard method, the carbon is cured while sandwiched between a solid mandrel and heat-shrink tape. When the tape comes off a rough exterior remains. A more expensive way to produce tubes is "inside out" or "molded" construction where carbon is wrapped around an inflatable mandrel and locked in a solid cavity. In this case the carbon is cured within a high-pressure and high-temperature mold---very similar to the method used by Reynolds to build our 500g Ouzo-Pro carbon tandem fork. Because the rough outer plies of a cheaper mandrel-wrapped tube must be partially destroyed (ground away) in order to produce a uniform exterior, a molded tube with the same weight and diameter can test 20% stronger. While many of the best framesets now include molded carbon forks and stays, Santana and Titus are, as yet, the only builders using molded frame tubes.

Second, a molded tube allows advanced geometric shapes. While Ben Serotta, for instance, clearly understands the importance of an externally-tapered downtube (a concept he pioneered 15 years ago), his carbon composite frames can't incorporate this advantage. Because of proprietary molds, Santana's Beyond not only includes a Serotta-inspired tapered downtube, it's the first carbon tandem with an oval bottom tube.

Third, the inflatable mandrel allows a carbon tube to be internally double-butted. Frames built from double butted tubing (no matter what the material) can be 25% lighter without increased risk of failure. In addition to being lighter and/or stronger, a double butted frame is also more comfortable. Double butted carbon tubes are another Santana/Titus exclusive.

Fourth, in addition to internal butting near the ends of each tube, the inflatable mandrel also allows added internal layers of unidirectional "stripes" of carbon at the right and left edges of our tubes. These thickened edges provide greater lateral stiffness while damping out vertical harshness. No other bicycle frame tubes (in any material) share this feature that is exclusive to Santana.

Fifth, the largest advantage of our molded tubing is IsoGrid --- a skeleton of Kevlar-wrapped carbon that is affixed to the mandrel before the other layers. The resulting tube with its internal lattice is not unlike an airplane's fuselage---where the thin skin is supported by an underlying network of supporting ribs. In the case of an IsoGrid tube, however, the application of heat and pressure permanently bonds the Kevlar/carbon ribs to the carbon skin.

Sixth, just as metals come in different gauges; sheets of carbon come in different ply weights. The thinnest plies, made from finer strands, can be built into tougher and lighter tubes. Further, additional layers allow a wider range of tuneability. Over 95% of the carbon sheeting used by the bicycle industry is "150" or higher FAW (Fiber Arial Weight). A very few items, including Reynolds' Ouzo Pro tandem fork, use super-premium 120 FAW carbon. Our Beyond uses ultra-exotic 90 FAW. The downside of thinner plies? Each sheet is more expensive and a higher number of plies means increased labor to produce the tube. Where else can you buy frames built with 90 FAW? Good question!

Seventh, just as "metal" includes a wide family of materials with various properties, "carbon" describes a range of complex hydrocarbons. Most carbons used in the bicycle industry are standard modulus---considerably less expensive than titanium. A few companies use intermediate modulus --- as expensive as titanium. High modulus carbons are exceptionally rare, and are too expensive for bicycle frames. But because the stiffness difference between standard and high modulus is a whopping 48%, Santana has decided to break the rules.

Eighth, just before the numerous layers of Kevlar/carbon IsoGrid ribs, unidirectional edge strands, butting plies and 90 FAW high modulus carbon are placed into the mold, a short section of thinwall titanium tubing is slid part way onto each extreme end. During the high temperature and high pressure molding process these titanium ends become permanently fused to the carbon. The resulting Bi/Fusion tube is all-carbon except for the short titanium tips.

Note: While IsoGrid and Bi/Fusion are independent technologies (that are owned, registered and patented by VyaTek, the tubes used by Santana and Titus are IsoGrid AND Bi/Fusion. In short, IsoGrid makes a carbon tube stronger and more damage resistant; Bi/Fusion makes a carbon tube weldable.

Ninth, to produce similar looking frames Merlin and Serotta glue carbon tubes into pre-welded titanium lugs. At the Santana and Titus workshops, there are no pots of glue. Instead, the Bi/Fusion tubes are mitered, and TIG-welded directly to each other. Because TIG joints are both stronger and lighter than glued joints, the process used by Titus and Santana is superior. Think of it this way: while glued-together aluminum frames were popular 15-20 years ago (Vitus, Alan, Trek, and many others), these heavier and/or weaker frames are no longer being produced.

Summary. While tandem buyers will naturally want to compare our new carbon Beyond with previous exotic frames built by Santana, Seven and Calfee, the numerous advantages of IsoGrid and Bi/Fusion technologies are undeniable.

For instance, when weighed on an accurate scale the Beyond frame is at least 15% lighter than the lightest previous carbon frames and 20% lighter than our titanium frames. When stressed on a precision testing jig the Beyond is stiffer than the stiffest frames built from steel or aluminum. And beneath our testers' delicate derrieres, the Beyond is supremely comfortable---most have rated it "twice as comfortable" as the tandem they currently own.

Mark again: "Very cool technology but I'm still waiting to see the cost..."

My reply: $9695 will get you a uniquely efficient and comfortable sub-30 pound tandem with a lifetime frame warranty and proven components. Gram shavers and competitors will be able to wring out an additional five pounds. Either way, you cannot buy a faster and lighter tandem at any price.

PS: Because tandeming is a reliable indicator of an evolved lifestyle, spending more signifies advanced intelligence.

PPS: Your neighbors already think you're crazy. Why not confirm it!

Some who responded to last weeks posts have questioned the effectiveness of the IsoGrid internal reinforcement, the strength and stiffness of the molded tubes, or the accuracy of the build process. These are the same tough questions I asked before investing in this new project.

Why did Santana jump at this opportunity? In the last post I explained that Santana had researched and rejected the three previous methods of carbon frame construction. The reason I proceeded with this project is that five months of research convinced me that this technology will allow Santana to produce tandem frames with unprecedented levels of performance.

I'll let Craig explain Carbonframes' gussetted process. With that exception builders have either glued plain gauge tubes into lugs, or molded a one-piece monocoque. (Before someone nitpicks: Yes, I realize some companies combine both methods by gluing partial monocoques). While monocoque forks have set new standards, one-piece frames have not yet lived up to their (still enormous) promise. Until monocoque frame construction comes of age, experiments are incredibly expensive (each size-specific mold for a single bike costs $8-10,000 and each immutable tandem mold will be 3x as expensive). If a builder pursues a non-monocoque direction, the problem with all other carbon fiber designs --- including Calfee's and Santana's --- is the weight of the resulting overlaps and/or joints.

With metal frames (steel, aluminum or titanium) the connection weight of a lugless TIG-welded frame is less than 1% of the weight of the frame. The connection weight of a composite frame is many times higher. In short, while carbon is supremely efficient between joints, it is woefully inefficient where connections exist. (Which explains why substituting a lightweight carbon-fiber rear triangle to an aluminum or titanium frame actually makes it heavier!) Though the shiny titanium sections of a Bi/Fusion frame may look heavy, the co-molded tips dramatically reduce connection weight by allowing carbon tubes to be welded directly to each other.

A number of people have asked to know the exact weight. The latest Beyond prototype, displayed at Interbike, weighed 5.71 pounds complete with paint and all welded fittings in a MEDIUM size (suitable for captains from 5'10" through 6'). When compared against other painted frames in the same size, the still-heavy prototype is more than a pound lighter than any carbon frame I'm aware of, two pounds lighter than a medium frame built from the lightest Easton aluminum tandem tubeset, and four pounds lighter than a Cannondale frame.

PS: When will the Beyond reach production? Now that our new frame jig and proprietary molds are finished, one final hurdle exists before production is scheduled. Next week an independent lab will pull apart some Bi/Fusion tubes with various-length overlaps to determine the correct length for the ti sections (which are currently too long). We'll also pull apart some same-diameter Easton tubes to make sure our carbon Beyond remains stronger than our current aluminum frames. While shorter ti sections won't get the weight under five pounds, I am confident that 2.50kg (5.5 pounds) is a realistic projection for a medium-size painted frame with all welded fittings.

PPS: Is weight the primary goal? Hardly. Every test rider so far has rated our current Beyond prototype both "stiffer" and "more comfortable" than any tandem frame they have previously ridden. While weight is the easiest way to compare tandem performance, I would argue that stiffness and comfort are better indicators of real world performance --- and owner satisfaction. If you are an experienced tandem team and will visit Southern California this winter, call our test-ride line at 909/ 596-7570 ext. 10 and leave a message with your names, phone number and current tandem.

A post and apology from Bill at Santana

While Craig Calfee and I would undoubtedly rather eat chocolate than quibble over definitions, he correctly noted that my claim about Serotta's Ottrot carbon/titanium frame was wrong. The Ottrot DOES include Ben's inspired conically tapered downtube design. Although our sport loves tubing with funny shapes, most of the claims about these shapes are bogus. Serotta's efficient "Colorado Concept" conically-tapered downtubes, on the other hand, are a proven way to increase a frame's efficiency. Sorry Ben.

I want to thank Calfee for his informative reply. Craig certainly has more experience with carbon than I. Additionally, while most carbon frames intro'd in the 80s are now obsolete, the gussetted design used by Carbonframes/Calfee has established an enviable track record. Incidentally, my bike shop was one of Carbonframes' first dealers, and Santana met and consulted with Craig's partner (Steve Levin) in 1992 to explore the idea of licensing their Carbonframes technology to produce a Santana carbon tandem.

I hope Craig does follow up with a closer look at the technologies offered by VyaTek --- especially IsoGrid (thinwall carbon with internal reinforcing ribs), which won the prestigious JEC Composites Innovation of the Year Award for 2002. I first met VyaTek's founder, Howard Lindsay, when he headed the sporting goods division of Simula, an NYSE-listed aerospace company. At a number of 1993-4 meetings we explored working together to produce a monocoque (one piece) carbon tandem frame. While a Santana project did not result, Simula subsequently produced the High Zoot brand of full-monocoque dual suspension mountain bikes. In 1996 Howard was recruited by True Temper and simultaneously held down two positions; V.P. of Engineering and R&D. In 1999, when Simula decided to sell the project he'd created, Lindsay left True Temper to purchase Simula's sporting goods division and its intellectual properties; which he renamed VyaTek.

While I am neither a research engineer (like Howard Lindsay) nor a hands-on builder (like Craig Calfee), my love of carbon for bike frames has a long history. In 1974, two years before founding Santana, I worked with Frank Appel (a toolmaker) and Dick Kantner (owner of Composites Development Corp.) to market the first-ever carbon fiber bike frames. That product --- named GRAPHITE/USA --- beat Exxon's GRAFTEK into production by a few months. Unfortunately, both brands had severe reliability issues. Our small team threw in the towel after a few dozen frames and then watched as Exxon poured hundreds of thousands of dollars down the drain. I subsequently spent two years as a consultant to AVCO Aerospace, who built a series of Boron-fiber frames that never reached production.

These early experiences, though, hardly soured me on composites. After my second GRAPHITE/USA frame became unglued (a pothole killed the first frame and a minor bump into the side of a turning car took out the second), I bought a Trek carbon frame that I still ride. In addition to hundreds of carbon frames from Look and Trek, my bike shop was the largest dealer for Kestrel from its founding until Kestrel was purchased by Schwinn (who canceled the dealership because I also owned Santana).

Santana also worked with our ex-employee Mike Melton when he built the world's first carbon fiber tandems while working at Huffy. Earlier Melton had been recruited from Santana to design the 1984 Olympic bikes for the medal-winning U.S. Team. In 1987 he built the two "Raleigh" carbon road tandems in Ohio for the Lon Haldeman / Pete Penseyres Transcontinental Record Ride while Santana produced a "Raleigh" track tandem in California for the U.S. Team to take to the World Championships. As for the world's first carbon tandems, one came unglued during the record crossing and the other is still being used (and was ridden at Santana's 2001 tour in Hawaii). Due to hefty weight and a 50% failure rate, no one at Huffy, Raleigh or Santana wanted to continue the carbon tandem project.

Summary: While I cannot claim Craig's experience, my involvement with carbon bicycle frames (and more recently forks) dates back to 1974. I have worked with numerous composites specialists and toured a number of facilities. And while I am hardly an expert in C-F construction, in 1987, 1992, and 1994, after consulting with leading specialists, I decided that Santana would not adopt one of the three older C-F technologies (glued together, gussetted, and monocoque) to build tandems.

What happened to change my mind? The next installment compares the different methods.

P.S. How important is weight? At Interbike I not only saw the gorgeous 68 pound Miyata tandem, I also saw a sub-10 pound single. Which famous builder got their racing bike below 10 pounds? Actually the used and privately-owned single was hidden in an out-of-the-way corner. I suspect there are numerous reasons that the lightest new bikes in famous builder's booths were many pounds heavier. For instance, would any 10-pound bike be stiff enough to win a sprint? Or ev en stable enough to be ridden in a crowded peleton? Looking at the components, I wondered if the bike would survive a century ride, or even a short section of cobblestones. While weight and dollars are the easiest factors to compare, my next post will detail three tougher-to-measure parameters that are arguably more important.

PPS: In addition to the Craig's excellent White Paper on carbon, another classic article you can find on the 'net is Scot Nicole's 6-chapter primer on frame materials. Chapter 5, written with the help of Steve Levin (the MIT-educated engineer who co-founded Carbonframes), is a great introduction to composites.

Carbon Tandem History

I'm glad to have a corrected version of the history of the first carbon tandems. I did talk with Mike Melton about this project both before and after the record ride, and assumed from those discussions that the first pair of carbon tandems had been built in Ohio. At that time Huffy owned all American rights to the Raleigh brand, Mike was head of Huffy's Bicycle Tech Center in Ohio, and Raleigh's "Technium" factory in Kent, WA was under the Huffy umbrella.

It makes perfect sense to me now that Mike Melton would have sub-contracted these glued frames to Dennis Bushnell (another talented ex-Santana employee) within the Kent facility where frames were being glued together on a production basis.

I also didn't know the story of the third C-F tandem that Dennis later built for himself. It was this tandem, now owned by Maurice King, that attended our Hawaii Tandem Tour in 2001. Maurice (the son of the man who bought the tandem from Dennis) thought his (repainted) C-F tandem was one of the transcon Raleighs.

In any case Dennis has confirmed reports I received from Melton, Haldemann and Penseyres---that the first pair of carbon fiber tandems were heavy, awkward and unreliable. And while Melton offered to assist Santana to produce a "glued" carbon tandem, he was hardly encouraging.

P.S. Do either of those first two carbon tandems still exist?

PPS: For the following summer's Race Across AMerica Pete and Lon rode a "Burley" titanium tandem that was actually designed and built in California by Gary Helfricht. After being overtaken by a team riding a Santana tandem (that went on to win the RAAM mens' tandem division), Pete and Lon dropped out. That year the winning RAAM mixed team also rode a Santana tandem, and posted a record time that still stands.

D. Bettge; letzte Änderung: 31.10.2003