Review: Rocky Mountain Thunderbolt 770

Editor’s Note: This review originally appeared in Dirt Rag Issue #180. To make sure you never miss a bike review, order a subscription today. You’ll be helping to support your independent mountain bike forum.

The Thunderbolt is an all-new offering in Rocky Mountain’s 2014 lineup. With its 120mm of front and rear travel, this 27.5-inch platform is Rocky’s general-purpose XC bike, slotting between the company’s Element XC race and Instinct trail bikes.

There are four models in the Thunderbolt lineup made from aluminum using Rocky Mountain’s SmoothLink suspension. This fully active design positions the rear chainstay pivot above the rear axle to keep the “average” chain-torque line parallel to the line between main pivot and rear pivot. According to Rocky Mountain, this configuration provides a wide gear range where pedaling neither compresses nor stiffens the suspension.

The flagship 770 model is decked out with a FOX Float remote CTD rear shock and 32 Float 120 FIT remote CTD fork (with thru-axle). On a 120mm XC-oriented bike, a 32mm fork seems the proper blend of weight consciousness and abuse-absorbing performance. No complaints from this XC guy.

The SmoothLink suspension feels very active over small bumps, offering supple compliance with little resistance to initial movement. I like it like that. For all-around recreational riding, I set the CTD (Climb-Trail-Descend) switch in the Descend mode (the lowest level of compression damping). During seated pedaling, there was very little suspension bob. It may seem counterintuitive, but I preferred the Descend mode for in-the-saddle climbing. The active suspension kept the rear wheel planted and clawing up sketchy inclines. Climbing prowess is one of this bike’s strong suits.

The firmer-feeling Trail mode came in handy on technically challenging trails that had me frequently moving in and out of the saddle or exerting a lot of body English. The bike felt more settled with the increased compression damping. I could see riders who prefer a firmer suspension platform sacrificing some initial compliance and running Trail mode as their default. Since pedaling out of the saddle would get the party bouncing, standing climbs were best dispatched in the Climb mode (lockout).

That’s the magic of an active suspension coupled with the remote CTD control. The suspension is super responsive by nature, but it can be fine-tuned via compression damping to match conditions and/or rider preferences. At the flip of a switch, you can have it your way. You want fries with that?

For a 120mm XC bike, the Thunderbolt feels surprisingly bottomless and capable at absorbing big hits. The SmoothLink suspension’s end-of-stroke spring rate ramps up to prevent harsh bottoming out without killing the responsiveness through the rest of the travel range. Just point those 27.5-inch wheels into the rubble and crank to daylight. There’s
 no wallow in the mid-range, and with the 12x142mm thru-axle securely tying the rear end together, the tail doesn’t wag the dog. Factor in the good pedaling performance and there’s no doubt that this is a very well-behaved XC suspension design.

Rocky Mountain gave this versatile XC rig all-arounder geometry to match its multitalented character. Short-ish 16.8-inch chainstays make for an agile bike that grooves across a packed dance floor without stepping on toes. The “lengthened from traditional Rocky Mountain designs” top tube stretches the wheelbase to an appropriately stable 45.3 inches. The short rear balances the long front, and the combination creates an XC bike that reacts nimbly in technical situations, yet feels sure-footed when carving a fast corner or letting ’er rip down a steep chute. The 24.2-inch top tube on the size large also plays well with the short-ish 80mm stem and 725mm-wide handlebar (both of the Race Face Turbine flavor).

The bike’s 68.5-degree head-tube angle is a balancing act in and of itself. The Thunderbolt’s steering response feels smack dab in the middle of the XC range: snappy without crossing the line into twitchy territory. The Thunderbolt doesn’t have the “plow factor” of slacker bikes, but that’s not a complaint; rather, it’s a reminder of this bike’s XC intent.

The 13-inch-tall bottom bracket helps keep the weight low-slung. Still, it wasn’t until I replaced the stock Race Face Turbine post with
a FOX D.O.S.S. dropper that the Thunderbolt’s needle moved from
the middle of the XC range into trail-bike play land. Dropping down enhanced high-speed stability and inspired me to carry more speed through corners. Lean, carve, repeat. Appropriately, the Thunderbolt provides both internal (stealth) cable routing as well as external cable guides for a dropper seatpost. Aesthetically, two remote controls (CTD and dropper) made for handlebar spaghetti, but functionally everything was duck soup.

The rate-limiting factor in corners was the cornering traction of the Continental X-King tires (27.5×2.2 inches). I could push the Thunder- bolt hard into a turn and everything would be fine and dandy until one or both of the tires would break free and skitter sideways. I under- stand that X-Kings are all-around XC tires, and Rocky Mountain’s product manager told me that the next tire in Conti’s lineup was “too far over to the trail side of riding” for the Thunderbolt’s intent. I get those points, but personally speaking, give me a set of Mountain King IIs and call it nirvana.

The stock X-Kings are tubeless-ready and come mounted on Stan’s NoTubes ZTR Crest rims (with tubeless-ready rim tape applied). I ditched the tubes, added my own valve stems and Stan’s NoTubes sealant, and rolled tubeless during this test. The ZTR Crests are sweet XC rims that would work great on race day, should one be so inclined.

Recently we learned that Rocky Mountain will trim this 770 model from the 2015 Thunderbolt lineup. The top shelf will be occupied by the new carbon Thunderbolt MSL series, which offers even shorter chainstays, lower stand-over, RIDE-9 adjustability, and new pivot technologies.

Moving forward, the aluminum Thunderbolt range will top out at the 750 model ($3,300). If you have $4,000 in your wallet and act fast, you may still be able to score a 770 while they last. Its component highlights include a Shimano XTR Shadow rear derailleur and XT shifters/brakes/hubs/front derailleur, a Race Face Turbine crankset and Team XC Press-Fit bottom bracket, and a Cane Creek 10-series headset.

The Thunderbolt is a versatile XC whip that is equally at home flying through open flow trails, slashing through tight spots, or hunker
ing down and powering through chunk. Be forewarned: Throwing 
a leg over this well-mannered 27.5-incher may induce a Goldilocks epiphany, when enlightenment strikes and everything feels “just right.” Go ahead, I dare you.