Charlie Cunningham’s 2012 Personal 29er: So Many Details – Tasshi Dennis & John Watson | The Radavist | A group of individuals who share a love of cycling and the outdoors.

The following post is a labor of love. Hours of tedious work went into not only documenting this bike but writing about it. It is by far the most ambitious story Tasshi Dennis from The Vintage MTB Workshop and John Watson have worked on. Charlie Cunningham was more important to the modern mountain and gravel bike movement than many know. His work spanned over four decades, and the bike you see here today was his personal bike.

Read on for a complete dissection of what has to be the most detailed bicycle ever to grace this humble corner of the internet. We hope you feel the love that was poured into this post…

The Mountain Bike Phenotype

Early mountain bikes trace back to a diversity of origins, from touring and BMX bikes to moto-cross and paperboy cruisers. Each had some characteristic that lent itself to riding off-road, whether it be knobby tires, stable geometry, ample suspension, or large tire volume. Or maybe it was just whatever bike was available at the moment. Of course, many of the most skilled frame builders of the time came from a background in skinny-tired road racing bikes, including Tom Ritchey, Joe Breeze, Chris Chance, and Ross Shafer.

As a result, many early mountain bikes had very refined frame construction that far exceeded the rough-and-tumble nature of their inherent use. But what about weight weenie road bikes from the 1970s with their “drillium” components, silk tubular tires, and raw titanium replacement parts? That connection seems about as far-fetched as one can get, and certainly not off-road worthy.

Aluminum Demigod

Before Charlie Cunningham built the world’s first aluminum mountain bike in 1979, he had been obsessed with shaving every-last-gram off a series of custom road bikes. This culminated in his 1974 Alan Competitzione whereby standard parts got replaced with custom-shaped bits of titanium, magnesium, exotic aluminum alloys, and plastic. The result was a sub-seventeen-pound noodle that was ill-suited to heavy use and in some situations, might see the front tire rub the downtube. Failures of weight weenie bikes were common and without warning.

However, as a superb finesse rider and one that weighed less than 140 pounds wet, Charlie made these spindly bikes continue to work for him when the fat-tire craze took off in the late 70s. A photo of him in a 1979 Repack downhill event is a testament to his riding skill and determination, riding what would appear to be his Alan. However, there is something else of significance here, and that’s the large wheel size. As a Berkeley-trained aerospace engineer, Charlie recognized early on that large-diameter wheels roll over obstacles better, while lightweight construction allows them to accelerate up to speed more quickly.

Charlie in 1979 riding Redpack and a 700c Expedition

After producing dozens of aluminum mountain bikes with smaller 26” wheels, Charlie built for himself what he called an Expedition, or Speed Racer, bike with a durable aluminum frame for bigger 700c wheels. With big aluminum tubes, it wasn’t a noodle, and in some instances, he even used slightly bigger 27” wheels. Today, we’d call it a gravel bike.

Of course, Charlie’s desire for big wheels was hampered at the time by the limited choice of tires with any significant volume. In the European 700c size he might find tires as big as 28 mm in diameter for touring bikes, while for 27” it was limited to 1-3/8” (about like today’s 32 mm cross tires) with low-quality gum-wall construction. Some relief came in the early 1990s with the Panaracer Smoke 700c and the Bruce Gordon Rock n’ Road, which were a cushy 43 to 45 mm width with small knobs.

Cunningham 26″/29″ Mullet Bike

The Push for 29er Tires

Production bikes such as the Diamond Back Overdrive and Bianchi Project 7 were built around the Smoke tire but classified more as “performance hybrids” rather than mountain bikes because the tire volume was still too small to prevent frequent pinch flats. With these larger tires in mind, Charlie would adapt one of his 26” hardtail bikes with suspension-corrected geometry to squeeze in a 700c front wheel with a special fork that had a minimal axle-to-crown distance to preserve the head angle. This mullet setup had just enough room for a 45 mm tire and was ridden extensively by Charlie for years.

A breakthrough occurred in 2001 when Wilderness Trail Bikes (WTB) was asked to develop a “29er” version of its popular Nanoraptor 2.1” tire. Finally, this was a big wheel tire with the volume required for rugged off-road use, and what Charlie had wanted to build a bike around for decades. This tire would be used by the likes of Gary Fisher, Kent Eriksen, Don Cook, and Wes Williams to pioneer modern big-wheel bikes. Unfortunately for Charlie’s efforts, it had been nearly ten years since he built his last aluminum mountain bike creation, and he would soon leave WTB.

Making matters worse, his post-weld heat treatment oven for frames had long gone into disrepair and been taken over by critters. The possibility of a 29er Cunningham would need to wait another ten years when two of his biggest devotees would motivate and fund him to rebuild his oven. The result in 2012 was the production of just three big-wheel Cunningham bikes, with the example presented here being the one Charlie built for himself. The bike would end up being his very last mountain bike, for which the word “unicorn” certainly comes to mind.

Charlie’s Last Mountain Bike

As it happened, this would not be the first 29er mountain bike Charlie would design from scratch. For racing the oldest bike at the 2008 Single Speed World Championships (a 1992 WTB Phoenix), Charlie’s wife, Jacquie Phelan, won a Mike DeSalvo custom frame. Having not been built yet, Charlie took the opportunity to think through the geometry for a custom 29er that both he and Jacquie could ride, enabling him to test out his thoughts for a big wheel bike without having to build and heat treat a frame himself.

Although he found the resulting rigid fork “horribly stiff” and the associated Shimano SLX hydraulic disc brakes grabby and “intentionally designed for peak power,” he very much liked how a modern 29er could be designed to roll. For his own bike, Charlie wanted a 29er that was nimble like a 26er with a short rear end, steep and quick handling, and light.

The frame itself follows the classic design of a late-model Cunningham, from the sloping toptube, big seatpost, rear-facing dropouts, and organically shaped gussets. Less obvious are the subtle hourglass shape of the headtube and concave center of the bottom bracket shell. Both items are internally hollowed out to save even more weight.

After heat treatment, the frames are a matte gray color, and finishing is done with Scotch Brite pads, which helps to hide irregularities and is easy to touch up. Charlie only welds the frame tubes, so all cable guides, brake bosses, and bottle mounts must be riveted and epoxied into place.

The fork is a tried-and-true Cunningham Type II, which Charlie designed in the very early 80s before unicrown fork blades first became available. Although it looks rather beefy for a steel fork, the Type II is a very compliant design. It uses very stout, bent crown tubes to which thinly butted 1-inch toptubes are socketed. While the ends of the fork blades are designed to flex a lot, the crown is not, and cleverly that’s exactly where the brakes are mounted.

The axle to crown is as short as possible at only 401 mm with just enough clearance for a 2.1” tire, so forget about the sacrilege of ever running a suspension fork. After frame construction one free parameter was the fork offset, to which Charlie built two forks. The first had an offset of 48 mm, while the one he settled on is 53 mm, to reduce the fork trail even further.

This is an indication of the fine-tuning Charlie was engaged in through real-world ride testing as he balanced the inherent stability of the bigger wheels with the desire for nimble handling. Early 29ers struggled with high trail and slow response until RockShox came out with a 51 mm offset option for the Reba fork.

Speaking of geometry, the headtube angle is road bike steep at 73.5º! The seat tube is similarly steep at 74º but on par with modern racing hardtails. Charlie was clearly aware that bigger 29er wheels would be sluggish compared to their 26er counterparts with the same frame geometry and wanted to keep the handling quick.

Although this might be too quick for most, it’s worth keeping in mind that a fully rigid bike doesn’t experience the geometry variations of a hardtail or full suspension bike during compression. As will be discussed later, Charlie went to great lengths to keep the chainstays as short as possible at 430 mm, in part by compromising the rear tire clearance; the largest that will fit is a 1.95 inch, and even that is very tight. The wheelbase comes in at 1070 mm or a touch over 42 inches, which, surprisingly, is equivalent to his late-80s Racer model 26er mountain bikes. In total, the length numbers have more in common with modern gravel bikes than mountain bikes.

As unique in appearance as the frame and fork may be, nearly all Cunninghams were outfitted with Charlie-made or -modified parts. This bike is no different. One’s eyes are immediately drawn to the scissor-style “Lever Link” brakes. As the last and best iteration of his patented Rollercam brake arm design dating back to the early 1980s, the mechanical actuation through a pair of linkages is the same as the Cane Creek eeBrake caliper.

By request, Charlie left the brake arms roughly milled rather than, in his words, “fiendishly” finishing them to look like they were made by a machine. Charlie always preferred that his bike visually say, “I was made with care by hand.” One intricate detail that sticks out is the wire hook with the brass ball soldered to it as a handle.

This is a security mechanism that keeps the threaded yoke of the upper linkage attached to the top of the arms so the brake cable tension can be run as low as possible, just enough to return the levers and arms to their fully open position. At that low tension, the brake arms could inadvertently disengage in rough conditions.

To drop a wheel out, the brake is opened at the yoke after loosening the hook. Threading the yoke in or out changes the leverage ratio and compensates for brake pad wear. Should the handlebars be turned too tightly, the top of the Lever Link brake would contact the downtube and be damaged, so Charlie developed a simple steering limiter. A parachute cord tether runs from a titanium strut attached to the back of the fork crown to an anchor point on the bottom of the downtube.

Steering is limited to about plus-and-minus 40º, which won’t allow you to perform Danny MacAskill trials moves or pull a 180 on a sidewalk but doesn’t prove to be a hindrance out on the trail. It’s for good reason that the brakes on this bike demand a lot of your attention!

The mismatched hubs are also worth examining, with a vintage Wilderness Trail Bikes Grease Guard hub in the front and a Chris King Classic tandem hub in the rear. While the bike is retro in style, the design has the modern element of “Boost” dropout spacing: 118 mm front and 145 mm rear. Charlie has long pushed the industry toward wider hub spacings to make wheels stronger, particularly 135 mm back in the late 1980s, as bikes started to add more gears and wheel dish got more severe.

The ultra-wide 118 mm spacing in the front–creating a wider spoke stance for a more laterally stiff and more vertically compliant wheel–dates far back to some of Charlie’s earliest personal bikes. The hubs are held in place with Charlie’s Slo-Release hub skewer design, which can only be loosened by inserting a separate pin to act as a lever to unscrew the conical end nuts. The wheelset can’t be stolen quickly, but even if it was it would only be fully compatible with two other bikes in the world!

The bike industry has largely settled on a couple of seat post sizes around 32 mm diameter which easily allow for telescopic dropper action. Long ago Charlie took the oversized concept much farther to a 1-3/8-inch size, or about 35 mm diameter, to provide the strength needed by his heavily sloping toptube frames with long seat post extensions.

The graceful curve of the post is fine-tuned by Charlie to create the offset needed to fit a particular rider. The saddle is essentially bolted directly to the top of the tube at a fixed angle, with tilt adjustment only possible by cutting a new angle. The design is light and strong but hardly user-friendly, although it rarely needs adjustment unless a different saddle is desired.

Charlie put in a heroic effort to have short 430 mm chainstays with a triple chainring crankset while also maintaining the narrow 154 mm Q-factor of a road bike (pedal-to-pedal spacing). Everything is tight everywhere and requires sub-millimeter modifications. Of course, the bikes of today solve this problem with single chainring drivetrains, as Charle’s first mountain bike did in 1979, but for various reasons such as chainline and durability, this bike has a triple.

The key to doing this while also maintaining the shortest possible bottom bracket spindle length was the use of Middleburn cranks. These old-school square taper cranks have a removable spider which allowed Charlie to mill down the back side interface so that the spider could sit farther out and be able to maintain the same chain line.

However, doing so caused the back of the right arm to contact the front derailleur cage, requiring the addition of more clearance to the arm. Elsewhere, Charlie modified the front derailleur to be able to swing closer to the frame. Oh, the power of a Dremel tool for these sorts of modifications. In the end there is practically no bottom bracket spindle showing, which is even more impressive since the bottom bracket shell is only 70 mm wide (not Charlie’s typical 80 mm). The front chainrings also show evidence of Charlie’s meticulous filing and Dremel work on the tooth profiles to optimize shifting. Cleverly, Charlie integrated an anti-chain suck feature into the same plate that keeps the brake bosses from flexing outward.

Other details worth mentioning include the modified Nitto bottle cage to allow for the use of a massive 1.5-liter Evian water bottle. A very minimalist tool kit is strapped under the saddle using innertube rubber bands and includes the pin for removing the wheels. Although Charlie used clipless pedals on his road bikes, his mountain bikes always used old-school clips and straps. Incidentally, his shoe of choice is the Ned Overend edition Ground Control from the mid-1990s.

The pedals started out as a pair of Shimano T-100 platform pedals designed for old-school triathlon use, to which Charlie bolted on modified Toe Flips, cage and platform extensions, guides for the straps, and various modifications to ease entry and exit. The bike weighs 23.25 pounds, which is even more impressive when you consider that there is no carbon used on the bike.

After looking at the numbers, it should come as no surprise that the bike rides like a rocket ship. It climbs technical terrain incredibly well while being a little nervous on the downhills. Charlie accomplished his goal of having the advantages of big wheels combined with low weight and the quick handling characteristics of the small wheel bikes he had ridden for decades.

If you object to some characteristic of his bikes, Charlie will simply tell you that “it’s optimized for the kind of riding I like to do.”

No one can argue with that. In the end, perhaps this is the bike Charlie really wanted to build for more than 30 years. Although Charlie no longer rides, this bike will continue to get used and put a smile on the face of the rider.

The Build: