Editor’s note: This story first appeared in Bicycle Times issue #18, published in August 2012. Words by Jeff Archer. Photos by Wes Stearns.
In the past few issues, we have looked at the pros and cons of several framebuilding materials and highlighted a vintage bike made from each material. So far, we have featured a steel Schwinn Paramount, a titanium Teledyne Titan, and a carbon fiber Graftek G1. This month, we will take a little detour and discuss a second carbon fiber bike, the 1990 Trimble Aero.
Last issue, we discussed carbon fiber’s high tensile strength, relatively low density and unique ability to be shaped. The Graftek used carbon-wrapped aluminum tubes bonded into a conventional-looking frame. This configuration didn’t take full advantage of carbon fiber’s strengths; the Trimble Aero does a much better job.
Several members of the Trimble family have designed and produced bikes and accessories from carbon fiber. Brent may be the best-known builder in the Trimble clan; his Inverse 4 mountain bike frames were among the most unusual in the 1990s. These frames used a single large-diameter composite tube that split into a pair of stays at the seat tube. The seat tube ended at the bottom bracket and a reinforcing brace between the bottom bracket and frame formed an upside-down (inverse) 4. Another brother, Richard “Roo” Trimble, designed and produced the Roobar, a one-piece composite mountain bike bar and stem combination.
Our feature Aero bike was designed by a third brother, James Trimble. James had noticed that the best RC model airplanes used monocoque construction and wondered if this construction technique could be applied to bicycles. Monocoque construction uses the outer skin to carry most, or all, of the structural load. James approached brothers Brent and Fred to help. They relied on boat-building techniques for the initial frames, with Brent doing much of the actual construction, using internal reinforcing ribs to beef up the outer skin. Since the frame wasn’t based on a conventional structure, the ribs could be placed in the optimal positions within the monocoque.
The cantilevered rear dropouts would absorb minor vibrations, and shocks from the rear wheel would be distributed along the entire frame instead of going straight up a conventional set of seatstays, resulting in a more comfortable ride.
Trimble also molded in pockets for the shifters and front derailleur to shield them from the wind. The rear wheel is also hidden from the wind, and cables are routed internally. There was the possibility of integrating a water bladder into the frame, but his bike uses a Trimble-designed behind-the-seat water bottle mount. While the frame is very aerodynamic, I suspect it would be difficult to control in a crosswind.
All of the advantages of using carbon fiber for bike frames can also be carried over to components. In 1990, there weren’t many road bike components being made from the material, but wheels were one exception. This bike has a carbon disc rear wheel and a carbon TriSpoke front wheel. These were not particularly light wheels, but complemented the Aero frame nicely.
Comparing the Trimble to the Graftek shows that bike designers have a difficult time in choosing the material, but an even tougher challenge in taking full advantage of that choice.
This bike can be seen at the Museum of Mountain Bike Art and Technology in historic downtown Statesville, North Carolina. If you can’t visit in person, check out the collection at www.mombat.org.