Cycling Science

Co-Motion's Co-Pilot

By: Chris Rutkowski

A great bike travels well with S&S Machine's Couplers

The idea of brazing a threaded coupler into a perfectly good piece of frame tubing sounds like blasphemy. According to the illuminati, variables like metallurgy, wall thicknesses, butting proportions and welding techniques (to name a few) are critical in creating a ride-worthy frame. Add a coupling in the middle of a tube? Sure. Any why not switch to rebar while we're at it?

Having been exposed to this litany for years, I had misgivings when I first swung a leg over Co-Motion's Co-Pilot. Thirty minutes earlier, the bike had been in a suitcase. Most of the intervening time was spent labeling the twenty-odd pieces of velcro'd frame padding for ease of future repacking. The frame, which started as two pieces joined at the top and down tubes by S&S Machine's Bicycle Torque Couplers (BTC), assembled in minutes into what looked like a fairly normal road bike. But how would it ride?

To make the long story short, about 5 miles into my first ride I forgot the BTCs were there; they didn't squeak, they didn't flex, they didn't draw attention to themselves in any way. Nada. Hmmmm. Later that day I talked a 190 lb. racer buddy into doing a few sprints; he came back reporting "no chain rub, no squeaks, plenty stiff". This was clearly a case where no news was good news. The couplings deliver exactly what they should: they assemble and disassemble easily but are otherwise unnoticed.

Which is not to say that the Co-pilot went unnoticed. Its sparkling blue metallic paint and flawless welds drew favorable comments from many riders in my club; this is a well-crafted bike. Interestingly, only one rider noticed the couplings before I pointed them out. Which makes an important point: the couplings are jewel-like in their own right and do not detract from t he aesthetics of a fine bike.


Forgetting the couplings for a moment, the Co-Pilot is a fine bike, period. Ridden aggressively on the rough pre-revolutionary farm roads of western NJ, the Co-pilot soaks up bumps as though suspended. High frequency road irregularities are felt, but with no harshness. At the same time, 45+ MPH descents were rock stable, no-hands riding is easy, and the steering at both high and low speeds is precise. This is a bike with a very wide performance and comfort envelope.

The frame is made of double-butted Tange tubes with a slightly oversized top tube. The couplings are silver brazed into the top and down tubes before they are cut and mitered, so alignment is perfect. The 56cm Co-Pilot had a roomy 56 cm top tube, with a 73 degree seat tube angle. This classic road geometry is coupled with longish 42 cm chain stays complete with rack-mount eyelets. Up front, a Kinesis aluminum fork and a 73.5 deg. head tube keep the handling precise while contributing to the smooth ride. There is a bit of toe-clip overlap, even with my size 9 shoes, which might be disconcerting to a rider who hadn't experienced it before.

According to Dwan Shepard of Co-Motion, standard equipment for the Co-Pilot is the Shimano 105 gruppo, and the buyer can choose from any of eight standard colors.

The down-tube shifters seemed under-spec'd on a $2000 bike, but since each bike is painted and built up to order, custom colors and component choices are easily accommodated. The test bike came equipped with an RX100 triple and 8-speed 105 components. Without pedals, the test bike weighed only 21.87 lbs.; very respectable for a 'travel bike' with a triple crank!


Because the bike packs into a 26"x26"x10" hardshell case with wheels and a handle (or the standard nylon case which transforms into a backpack!), it can be checked as luggage without special handling charges. But more importantly, the case fits into the back seat of my Honda Accord; so taxis, trains, boats and elevators, which present a gauntlet of problems when lugging a standard bike box, are quite manageable.

This convenience does not come cheap. The couplings add something between $200-$500 to the price of a new frame. But as always, price must be compared with value. Frequent-flyers who currently take their road bike along would recoup this after only five round-trips.

But the real market may consist of the many riders who, like me, don't consider taking their bike on trips because of the hassle factor. For example, last year I went to Switzerland on a three week business trip - the bike stayed home; likewise on a trip to northern California last summer; and to Interbike just a few weeks ago.....I didn't even consider taking a bike. Not, if my bike had been equipped with BTCs.... I probably would have considered it - and maybe I'd have learned to yodel and climb at the same time.


From my viewpoint, a coupling designed to join bicycle frame tubes has to meet three criteria: it must withstand a wide variety of loads, it must not introduce slop into the structure, and it must look good. S&S's BTCs score high on all three counts.

The BTCs are made from 17-4 (Chromium-Nickel) Stainless steel, described by various makers as suitable in "a variety of critical applications" such as "jet engine parts", and "nuclear reactor components". Certified test reports show that the lugs have an average yield strength of 141.5 KSI (thousand lbs. per sq. in.). Point is, the BTCs are tough. And not just on paper. Steve Smilanick, president of S&S Machine, demonstrated a few delightful torture machines at the Anaheim Interbike show which applied torsional, tensile and bending loads to pieces of bicycle tubing with couplings silver brazed in place. When stressed, the tubing portions show dramatically greater distortion than the couplings.

Fig. 1 shows what happened when a 32.4" piece of tubing with a coupling installed 3.5 inches from one end (approximately the same as in top and downtube installations) was stressed to failure; the tubing gave out first.


On the Co-Motion bike, the BTCs gave no evidence of play. The reason is evident in the design. Look at the photo of the coupling: the interlocking teeth have beveled sides that match opposing bevels on the opposite piece. The net effect is of a trapezoidal peg in a trapezoidal hole. The degree that the surfaces are parallel, the coupler is self-aligning and self-adjusting.

To achieve the required degree of parallelism and perpendicularity (the design is spec'd to .001") machining to high standards is required. Never one to do anything halfway, Steve brought in a Mazak Multiplex CNC machine (in effect dual CNC lathes with full milling capability at each position) which enables the lugs to be made without changing fixtures! With accuracy and repeatability to .0001" (1/25 of a human hair), 100% of the pieces made easily meet the specification. (oh, in case you want one for yourself, the price tag was in excess of $400,000.....)


The BTC's have an aerospace gleam that would look at home piping anti-matter around the Starship Enterprise. The test bike looked great; one bike on display at the S&S booth at Interbike (sporting a two-tone paint job split at the couplers) was a visual knockout.


I started off thinking of the Co-Pilot as a travel bike because that's what Co-Motion called it. But I ended up thinking of it as a great bike that travels well. All you Product Managers out there would do well to consider this distinction carefully. There is a potential market for bikes equipped with BTCs (as opposed to a kinetic market) which is being largely ignored.

For most riders, a travel bike is perceived as a luxury, sitting somewhere after road, MTB and beater bikes on our budgets. But the Co-Pilot is worth considering as a primary ride; the BTCs add to the bike rather than compromise it.

Aside from price, the only perceived downside is weight. But two BTCs add only 8 ozs. to the finished bike, which amounts to a fraction of a water bottle. Gram-shavers will be happy to know that a new Ti version cuts the weight "penalty" to more like 5 oz. - and will soon be available from Co-Motion, Merlin, and others who build Ti frames.

The bottom line is this: due to S&S Machine's BTCs, travel-worthiness should now be thought of as a value-added option on any good bike, not a raison d'etre for a niche product. Twenty seven frame makers now offer BTCs; but very few riders know of the BTC's existence, let alone appreciate what it can do for them. Spread the word.

(Figure 1 and Photo of coupling were not included in this reproduction)

Winter "95
Copied with permission from
Cycling Science/Penner Publishing Inc.
P.O. Box 926
Highstown, NJ 08520
Telephone (609) 443-0038
Fax. (609) 443-4471

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