My pasty forearms were feeling their first sunshine in months as we dropped in on the scrappiest, crappiest and only trails yet rideable. April in Vermont. Locals have just begun telling tall tales of dry dirt in officially closed networks. It's that time of year when we go in search of clear singletrack at informal networks that, if they weren't running unopposed, surely wouldn't be elected as the trails du jour.
Struggling through the leaf-covered spaghetti of rocks and roots, around corners intended to be walked, not ridden, and abruptly encountering occasional drops and roll-ins, it occurred to me that I couldn't have chosen a better bike for the job.
Rocky Mountain's New Thunderbolt
Like the Instinct and Altitude, the new Thunderbolt has been tidied up with an all-new frame that boasts an updated linkage, complete with hidden chainstay pivots. Cables run internally and there's room for both a bottle cage and 27.5 x 2.5-inch tires. It can also run 26 x 2.8-inch tires, which means that YES! you can finally use those wide-rimmed, Boost-spaced 26-inch wheels you have laying around. No front derailleurs, though.
Rocky Mountain categorizes the Thunderbolt as an XC bike, but you should take that about as seriously as the bike itself: not very. That's especially true of the burlier and badderer BC Edition tested here, which totes more travel and slackness than the rest of the lineup.
To get specific, this 27.5-inch-wheeled jokester gets an additional 10 millimeters of travel at both ends. Those 140 millimeters are delivered by a Fox 36 in place of the slightly more spindly forks that come standard on the non-BC models, and a longer stroke shock. The Thunderbolt's shape and attitude are determined by Rocky's Ride-9 system, adjusted by chips nested in the rocker link. Rotating the chips within their housing takes two Allen keys and just a couple minutes, and allows the rider their druthers of head angles between 65.9- and 67.1-degrees. As the head angle slackens, so does the seat tube angle. Other side-effects include increased BB drop, lengthened wheelbase, higher stack, shorter reach and a slightly longer rear center.
The frame is suspended by a Fox 36 Performance Elite fork and a Float DPS Evol Performance Elite shock. Fox also handles dropper duties with its Performance Elite Transfer post. A SRAM GX Eagle drivetrain and Guide RS brakes are paired with Stan's Arch MK3 rims, which are laced to a DT Swiss 350 rear hub and a Rocky Mountain house-brand front hub. This edition of the Thunderbolt gets burlier tires than the rest: Maxxis Minion DHF and DHR tires with 3C Maxx Terra casings indicate that it's ready to board the hein train.
Ride the Lightning
I started out with the Ride 9 chip in its stock, neutral setting. The first trait I noticed aboard the Thunderbolt was how supple the fork felt. I've been riding a lot of bikes with 34s on them, and even with the FIT4 damper, the 36 feels considerably more active and predictable over repetitive hits. It helps give the bike a stable feel, which is complemented by the frame's overall stiffness. Whether pedaling hard or thwacking into a corner, the Thunderbolt never flinched. But I'm also only 165 pounds.
That stoutness helped inspire me to try a few drops and rollers that I hadn't ridden before and probably wouldn't try for the first time on most 140-millimeter 27.5 bikes.
Like most 140-millimeter 27.5 bikes, though, the Thunderbolt is fleet-footed and intuitively controlled when jabbing through tight corners and up punchy, technical climbs. Some of the new, super-long bikes make me feel like I've shown up drunk for a jiujitsu tournament when the trail gets technical and levels out or—God forbid—goes uphill. The Thunderbolt isn't old school by any stretch, but its geo is conservative. And I think that's a good thing for a 27.5 bike in this travel range: If I'm buying a bike like the Thunderbolt, I want it to be quick and playful. A sub-1,200-millimeter wheelbase goes a long way toward that end, though it doesn’t make for the most stable-feeling ride at eye-watering speeds.
A 425-millimeter rear-center helps with its liveliness, too. Lofting the front end is no challenge, even for someone who hasn't learned to sustain a manual on a mountain bike. At first though, I couldn't get the rear suspension to match the geometry's bubbly disposition without sacrificing small-bump compliance. I was near the fast end of the rebound range on the shock at 29-percent sag, so I wound up running the Open-mode low-speed compression in the middle position. This provided the support and pop I was looking for without too much consequence when the going got rough. After a month of riding with plenty of hard, flat landings, G-outs and cased jumps, I have yet to feel any harsh bottom-outs.
Given how capable it is, I think the Thunderbolt would benefit from a more sophisticated shock. Something like Fox's DPX2 would keep pace with the 36, and allow riders to get the most out of the frame's 140 millimeters of travel.
Despite the limitations of the shock, the Thunderbolt feels well-suited to its slacker settings. In fact, the change was hardly noticeable except for while pedaling over high roots or rocks, where pedal strikes became more difficult to avoid due to the increased bottom-bracket drop.
It's a confident-feeling bike in ‘Neutral,’ but the slacker setting allows the rider to take advantage of the frame's stoutness and push the bike closer to its limit. I frequently adjusted the Ride 9 setting between Neutral and Slack to suit the day's terrain, but never spent more than 20 minutes in the steeper settings because they didn't seem to suit the bike, or my intentions for it.
In its slacker settings, the Thunderbolt's intentions approach those of Norco's Sight and Cannondale's Trigger. Both of those have plusher rear suspension, but the Thunderbolt gives the rider a level of adjustability that neither of those offer. Another worthy comparison is Spot's Rollik 557, which is a more efficient pedaler. The Thunderbolt is calmer in hairy, high-speed situations, and less apt to break traction when under power, helping it to excel on technical climbs.
Ride it in Neutral and you've got a playful, quick-witted and stout trail bike. Switch to Slack when you're ready to smash. But I wouldn’t bother with the steeper settings. This is not an XC bike.