The seed for this collection of superlight mountain bikes was planted when Kestrel offered us its most exotic composite monocoque frameset, the CS–X EMS, outfitted with a wish list of gossamer componentry at a weight of less than 20 pounds. I said the same thing you would: Yes, please.
  For a year I´d been riding a steel–frame KHS mountain bike whittled to 22 pounds by parts swapping, so I knew lightness wasn´t the exclusive domain of composite technology. Thus, I chose an aluminum Klein, titanium McMahon, and steel Steelman to represent the other commonly used frame materials and fill out the test.
  They have stiff competition (figuratively and literally) because the Kestrel is as impressively rigid as it is light, with reasonable comfort to boot. Up front, there´s the smooth resilience of the Ritchey Logic chrome-moly unicrown fork, which flexes visibly without feeling squirrelly. The frame´s subtle smoothness comes not from flexing tubes—the Kestrel´s don´t, to any significant degree—but from their shock´eating composite layers. Vibration is stopped, not passed to the rider.
  There are lots of ways to make a sweet–riding bike, but when minimal weight is desired it´s tough to beat the combination of composites and monocoque construction. The various "tube" shapes (technically, the frame is one piece) triangulate and reinforce each member against specific forces. This compliments composites´ strength–in–tension properties, allowing the orientation of structural fibers to subdue the stresses of each location. There´s no need for extra material, as with metals.
  So much for theory. The proof, as they say, is in the pedalin´, and the EMS saw a lot of action under me and technical editor Fred Zahradnik in Pennsylvania and Colorado. Most impressive to Dr. Z was the lack of flex at the bottom bracket, along the top tube, and at the rear brake bosses. Yet the Frame weighs just 3.25 pounds, and the bike is an incredible 19.65 pounds. Being a care–ful, smooth rider, Fred didn´t drop off a cliff or broadside any aspens while in Crested Butte, but he remembers hearing a couple large rocks whack the down tube during descents.
  Kestrel sent the EMS with 172.5–mm Ritchey cranks, the same length Fred rides on road. Although I prefer longer ones off road, Fred says they didn´t hinder his climbing ability. Not so the gearing—an optimistic 13–24T SunTour steel freewheel, which he eventually swapped for a wider range. The irony is, Kestrel chose such esoteric weight savers as squishy–feeling CLB aluminum alloy brake cable housing, and used alloy brake cable adjuster barrels in place of allen–bolt brake fixing bolts, yet missed a chance to come half a pound closer to the elusive 19–pound barrier by installing a Campagnolo alloy Cluster (not the most durable off–road cogs, but no less realistic than a 24T low). Also absent was the lighter, WCS version of the Ritchey Force tires, which, with the Campy block, would certainly have put the bike at 19 pounds (see "Lighter Than Lite," page 123). Kestrel recovered nicely, in my book, with the lightness and beauty of the polished titanium stem, handmade by Arctos Machine´s

Gary Helfrich. Fred put the bike´s Aerosports carbon fiber seatpost in the "stupid light" category because of its flex, but I rather appreciated how it muted washboard bumps when I was too lazy or too hammered to lift my butt one more time.
  But now that you´re salivating over the chance to swap your firstborn for an EMS, wipe your chin and prepare to wait. According to Kestrel´s Tom French, plans to produce the bike have been "totally shelved." He says our test frame was a "one–off... never intended for production as is." lt was made in California of "off–the–shelf" U.S. unidirectional material, not in Kestrel´s Japanese factory using special–order fibers.
  Make that "two–off" because our bike had a hand–laid–up brother that broke at the right chainstay after a week of testing by another publication. Ours must have been made of sterner stuff because it endured everything we put it through, plus some bunny hopping by man–mountain contributing editor Capt. Dondo, with nothing worse than a minor chainsuck scar on the stay.
  But take heart because a lighter version of the standard, 3.6–pound (for 19.5–inch) Kestrel CS–X may be introduced in ´92. The eventual production frame, tentatively named the CS–Xi (for its intermediate–grade carbon fiber), will weigh virtually the same as our EMS, French says, but will be tougher by virtue of more composite material. Offsetting the resulting weight will be a light aluminum alloy seat binder and tube assembly vs. the EMS´s steel pieces. It will also cost several hundred dollars less than the EMS would have, he says, but a price has yet to be set.
   Ride qualities should be the same as our EMS, French adds, which means the "i" will be a hot ride, indeed.