Carbon Fiber is a bike material that is enjoying a coming-of-age, or it sure seems that way. While it’s not a new thing, and it’s even an expectation in the road bike arena now, carbon fiber for use in anything but the most expensive cross-country race bikes is something that we’ve just begun to readily accept as an industry in the last few years. I’ve been enjoying an Ibis Mojo SL since last fall and the introduction of the new Santa Cruz Nomad Carbon and Ibis Mojo HD got me thinking over the weekend about my interest for the material and my experiences with it.
I grew up in Northwest Arkansas, and began racing mountain bikes in 1991. At the time, there was a core group of fast guys that called themselves the Bushmen. At the helm was a perennial fast guy named Scott Carroll, and he and a few others rode Trimble Inverted 4 carbon bikes. The frames were fascinating, like no other. And since these guys rode fast, I associated their performance with the bike. Was it a miracle machine? Probably not. In fact, one of the most miraculous aspects of Trimble’s bikes was that they had a fairly reliable failure rate.
But the bikes that broke were raced often and raced hard, and Trimble wasn’t scared to make a sub 3lb frame for Scott and the boys. They raced, they went super fast, and the frames lasted a season or so. While it may not have been the best for PR purposes, the lightweight frames were what the racers wanted and Trimble didn’t hesitate to build ’em. In fact, he always repaired them when they broke. I saw one of his bikes get nearly torn in half after a nasty impact with a tree. He put that one back together and it got ridden for another year before it was sold and I lost track of it. It’s a testament to the material and its repairability. Craig Calfee knows this as well as anyone. He’s a master at carbon repair.
I loved hearing stories about Brent Trimble, how he started with Kestrel, patented the bladder molding process, and designed their 4000 road frame. I heard that he even built the disc wheels that got used by the US. National team at the ’84 Olympics. I also loved hearing about how odd he was, preferring to tinker in a barn in his backyard about 45 minutes away from my home in Rogers, Arkansas. He called Scott, Homer. And Homer used to go help Brent with some of the manufacture and finish work of the bikes. Scott was an engineering student and an excellent scammer. I assume the bike building process was intriguing as a student, but I’ll bet he was in it for the free frames.
The Trimble family was always a bit of an interest. I’ve heard so many stories about this band of brothers, geniuses one and all I’d heard. They are engineers, architects, and who knows what, but they had a reputation for creativity. I’d seen James Trimble’s aero bike. It was basically a flat sail with two wheels. If ever there was a canvas for a dragon mural on a bike frame this was it. Roo Trimble built a one-piece carbon handlebar/stem combo and at one point modified one of Brent’s mountain bike frames, creating a unified rear triangle rear suspension. The swingarm pulled a cable that attached from the bottom bracket to the down tube with a pouch in the middle that contained a football bladder or inner tube. This whole apparatus was called the ‘Gizbag’…or so I heard. I never saw it in person.
The air of mystery surrounding the Trimble clan made them the local equivalent of a bike building bigfoot. Here were these guys, enjoying the creative freedom of a material that was exclusively used in aerospace applications. It was expensive and hard to work with. Or that was the reputation. I’d find out later that it isn’t necessarily difficult to build a bike with composites. It’s just hard to build a great bike, and quite easy to make a piece of shit or worse yet, waste a ton of expensive material and end up with a hardened mess of resin and bungled fabric equivalent to a $400 booger covered spitwad.
I was a kayaker before I started racing bikes and paddled what were known as Squirt Boats. They were designed to sink at will, bearing smaller volumes than traditional whitewater kayaks. The evolution of freestyle kayaking started with these tiny boats. Anyway, the sharp edges and highly sculpted design (necessary to develop the shape literally around and over the knees and feet) couldn’t be created with rotomolded plastics, not that any of the big manufacturers wanted to invest in this niche corner of the paddling market. So if you’re a long term squirt boater, you quickly become familiar with composites or you don’t paddle. Boat repair is something that you learn as part of the deal. I even cut my boat in half once, to ‘chop’ some volume out of it. Putting it back together was simultaneously scary, infuriating, and oh-so satisfying. I learned a lot by reading books and making sloppy patches for my edges, but eventually at least learned what not to do and started repairing friend’s boats as well. Fiberglass, Kevlar, and epoxy became a normal part of my vocabulary.
My boating experiences combined with my newfound love of mountain biking to fuel this craving to learn more about composites in bike frames. This is part of why the Trimble stories were so fascinating. As far as I was concerned, those guys dreamed it, and did it!
The Trimble frames cost $1200 at the time. It was s serious sum of money back then, and with their reputation as race only frames with suspect durability, I certainly never conjured up the cash up for one. The lightweight frames cost even more, about $1600. But I rode them a few times and let me say, that besides the unmistakably unique appearance, they rode very different from my Stumpjumper. The monostay rear end was definitely more flexible than a traditional double diamond bike frame, but on the trail, it seemed to just work. The Trimble frames were supremely comfortable, for a hardtail anyway. The bikes disappeared underneath you, and seemed to be tailor-made for rocky trails.
There was a kayak-builder up in Kansas, a couple hours north of us, who began to experiment with composite bike frames as well. Paul Bishop and his son Noah, unveiled a laminated wood mockup of their soon-to-be full carbon elevated chainstay mountain frame at the Devils Den Mountain Bike Festival. It looked similar to the Kestrel MX-Z. The details of the bike are a bit fuzzy these days, but I recall that they made a few carbon frames as well. The Bishop men were crafty fabricators too and always had their hands into something interesting whether bikes or boats, but the fun stuff was all just spare time piddling, if you will. Their bread and butter was tool and pattern making, and they had to pay the bills of course. So it may have been a case of ‘Bird in hand…’ I hear that at least one of their Genesis elevated chainstay bikes is still complete and gets ridden on a regular basis up there in Frontenac.
I can’t remember the exact moment of inspiration. Maybe there wasn’t one, but I decided to put away my torch and steel tubes, as I’d been making my own traditional bike frames for a few years, for an experiment in composites. I’d gotten my hands on a two-piece Trimble Inverted Four (it started out as one piece, of course) and zip-sawed it in half along its length. So I studied the cutaway pieces, how many layers did Brent use here? And there? I did my best to imagine the bladder technique he’d used to compress the laminate in the mold. I asked Homer questions about his process every time we met on the road or out on the trails. What kind of material was the bladder made from? He didn’t know exactly. I imagined my design and how it’d be different, something to call my own.
I appreciated the simple design of Trimble’s bike. In terms of the handwork in the mold, it was about as easy as it gets for a bike frame. Though I wanted mine to be easier, being a know-nothing goob. Keep it simple stupid! That was what my brother was learning in his engineering classes, and it sure sounded like good advice. Trimble’s frames often broke at the front derailleur clamp, and his cable routing was always tricky. When I’d begun my project, Shimano’s E-Clamp was available. I decided it was the magic bullet, and I’d do away with the small diameter ‘seat tube’ section required for clamp type derailleurs of the day. It would simplify my layup and make for an easier time as I learned along the way.
To be continued…