Do you remember two years ago, when this column reviewed the "29er," which had come to dominate the mountain bike world with super-fast, roll-over-anything, monster-truck 29-inch wheels that made traditional 26-inch bikes look like children's toys? Well, forget about that. Big tires still rule, only they're not as big. The new king is 27.5 inches, a size virtually unknown two years ago. Almost overnight, the 27.5 has become the de facto standard of the mountain bike world for several reasons: Compared with 29ers, 27.5s have quicker handling on trickier trails, easier acceleration and pedal turnover on steep climbs, fit shorter people better with less pedal-tire overlap and have less of a steroid-freak look. The 27.5s roll over bumps and drop-offs faster than 26ers and have greater rolling momentum and raw speed, just slightly slower than 29ers. With most of the benefits of the 29ers and none of their drawbacks, 27.5s are now acclaimed by mountain bikers as the best of both worlds. That is, until the next new size comes along.
Cannondale Trigger 27.5 Carbon 2: The adjustable-suspension 20-speed carbon-framed cross-country bike has a rear shock that can change from 140 millimeters of travel (5.5 inches) to 85 mm (3.4 inches). It also includes a 140 mm adjustable-rebound Lefty fork that can be functionally locked out. Top-end models run from the Carbon 2 at $6,170 to the Carbon Black at $10,000; aluminum Triggers with a conventional Fox fork run $3,500 and $2,900.
Likes: It has 2-in-1 versatility. The DYAD two-section shock, activated by a simple handlebar control, lets you switch the rear shock between long travel and short travel, depending on the trail condition and your riding style. You can customize your travel and geometry for climbing or descending. The oversized Lefty SuperMax fork (found on the carbon models but not the aluminum-framed models) has a near lockout/limited mode that is fine for climbing. The frame is rock solid, using through-axles at the key pivots to stiffen the swing arm. The Carbon 2 model includes SRAM X7 front and Shimano XT rear derailleurs and a dropper seat post.
Price: $6,170. www.cannondale.com
Pivot Mach 4 27.5: This lightweight cross-country race and endurance bike has 115 mm (about 5 inches) of suspension travel and a "DW" suspension design that claims to eliminate pedal-induced bobbing. It also claims to be the first Shimano electronic-shifting-compatible frame, featuring an internal battery mount inside the down tube.
Likes: Fast, with great handling and climbing. Brand new and beautiful, the design is built around DW suspension (named for inventor Dave Weagle), which delivers a plush, forgiving ride that pedals like a less-suspended race bike and delivers the holy grail of dual suspension: no up-and-down bobbing as you push the pedals. That lack of "squat" (as it is technically known) also translates to better handling by allowing a lower-center-of-gravity design with bottom bracket/cranks positioned a half-inch lower than similar bikes. Despite that, my pedals didn't smack the ground more than normal. Full bikes can weight as little 22 pounds. It keeps a clean look with ports for internal cable routing.
Price: $4,499 (Shimano XT/SLX) to $8,999 (Shimano Di2 XTR). Frame with top-end Fox fork is $2,899. pivotcycles.com
Back in the saddle
Mongoose Teocali Expert: It's an affordable, aluminum, big-travel suspension "Enduro" trail bike with 30-speed Shimano XT/SLX drivetrain and 150 mm rear and 160 mm front suspension travel. The suspension design uses popular and proven four-bar "Horst-Link" rear suspension.
Likes: It rides great. With 6 inches of travel front and rear, it can handle big hits, all-day rides and endless rocky descents. I threw everything I had at this bike in a four-hour ride in the Wasatch Mountains and had no sense that the Mongoose brand had been out of the high-end bike business for several years. This is a good comeback bike, very well appointed for the prices, with good parts all around. The Horst-Link suspension is the same used by top brands like Specialized.
Dislikes: Bottle cage mount on the down tube was too high; I could barely squeeze a small bottle in there (it might have been an early production model). It is being sold only consumer-direct; I like to have a dealer to go back to.
Price: $2,800 (Expert); $2,300 (lower-end Comp model). www.mongoose.com
Sensitive to bumps
GT Helion Comp 27.5: The aluminum-framed, 27-speed cross-country dual-suspension marathon bike has a long wheelbase, 110 mm of travel and a suspension design that specializes in sucking up small bumps.
Likes: Fast, light and smooth. The smoothness is due to its novel AOS design — angle optimized suspension — which reduces pedal-induced bobbing feedback, stops the chain from flopping around and seems to eat the relentless small bumps that can leave you fatigued the last half of the ride. AOS utilizes a high-pivot swing arm and movable bottom bracket/crank set that is not conventionally fixed in place, resulting in a gentle back-and-up rear-wheel path when encountering a bump. This "small-bump sensitivity" constantly reduces vibration and takes the edge off. The long wheelbase, balanced by a short stem, adds to the smoothness. At the same time, massive seat stays provide good power transfer and feedback. Includes 27-speed Shimano SLX and Alivio drivetrain and a handy remote fork lockout level on the handlebar.
Price: $2,300 (models at $1,500, rising to $7,000 for the carbon Elite model). www.gtbicycles.com
Wallack is co-author of "Bike for Life: How to Ride to 100." firstname.lastname@example.org