The Jeffsy sits in the middle of YT's three-bike range, sandwiched between their enduro sled, the Capra and their self-described 'everyday trail bike', the shorter travel Izzo. With 150mm suspension and sensibilities that are burly enough to plunge down the vast majority of descents without becoming a total drag to pedal back up again, like the very best trail bikes, the Jeffsy is an excellent jack of all-mountain trades.
For information on Bike Perfect's testing procedures and how our scoring system works, see our how we test page.
Here in its top-of-the-line Uncaged 6 guise, four other models are available, this highly capable bike comes bristling with the latest cutting-edge suspension tech from SRAM and a whole suite of electronic AXS componentry. So how does this tech-packed Jeffsy ride and is the hefty outlay for the latest trail blasting armaments worth the significant investment?
Design and geometry
Perhaps aside from the intriguing Flight Attendant modules on top of the right-hand fork stanchion and piggybacking the rear shock, the second thing that strikes you about this Uncaged 6 edition Jeffsy is how clean it looks. The only obvious cabling being the front brake hose (the rear neatly disappears into the frame behind the head tube until reappearing as close to the brake as possible). AXS and Flight Attendant wizardry means no gear or dropper clutter as all the constituent parts communicate wirelessly over the ether.
Like many other modern bikes, our large-sized test bike comes with a flip-chip that lets you adjust key geometry numbers by half a degree. The head angle can be 66 or 66.5 degrees, the seat tube angle: 77 or 77.5 degrees, and the bottom bracket height 344 or 352mm. The reach comes in a 470mm, while the chainstays are 435mm.
The current Jeffsy frame has been around for a little while now, so numbers on the head angle and reach look a tad conservative when compared to more recently released bikes in the same category, such as the Santa Cruz Hightower and the latest Canyon Spectrals, but in no way do that hold the Jeffsy back from being a proper trail ripper.
Components and build
If you're into the latest bike tech, this Jeffsy Uncaged 6 is pretty much your dream build. Electronic, auto-adjusting front and rear Flight Attendant suspension is the obvious highlight – which comes built into a top-of-line RockShox pairing of a 150mm Lyrik Ultimate fork with DebonAir + internals and SuperDeluxe Ultimate shock with an RCT 3 cartridge. As things stand, all Flight Attendant equipped bikes also come with wireless electronic SRAM AXS Eagle drivetrain and AXS Reverb dropper post too. Left hand controls let you manage saddle height and can manually select the suspension bias via the rocker shifter – the right-hand rocker shifter lets you select gears as usual. To complete the SRAM groupset, the Jeffsy comes equipped with powerful yet controlled G2 Ultimate brakes.
Somewhat overshadowed by the futuristic tech, but just as much a key part of what makes this bike special is the equally fancy 29-inch Crankbrothers Enduro Carbon wheels with an Industry 9 Hydra freehub. The freehub has 0.52-degree engagement, which in practice means an instantaneous drivetrain response – which is a great match for the ultra reactive rims. The wheels are shod with a super surefooted Maxxis pairing of the triple compound, EXO cased Minion DHF and Minion DHR II tires.
Piloting controls come courtesy of a 780mm Renthal Fat Bar Carbon 35 and 50mm Renthal Apex 35 stem. Between seat tube, shock and downtube is just enough room for a stubby Fidlock bottle to nestle in place. Despite being short and squat, the cunningly designed bottle can hold 360ml – which is pretty much the same as a standard bottle. But even on a nine-grand bike, while the Fidlock mount comes as standard, the plastic bottle is an extra purchase.
Performance
From the auto-adjusting suspension to the instantaneous drivetrain engagement, as soon as you begin turning the pedals, the ultra-responsive nature of the Uncaged 6 is hard to ignore. Everywhere I rode, the bike felt as if it was champing at the bit to go faster and hit the trails harder.
On undulating and upward facing terrain, the Flight Attendant suspension is superb but soon taken for granted – as I discovered when jumping onto a conventional MTB after several straight weeks on the Jeffsy. Essentially, the system reads the terrain you're on and auto-adjusts to give the optimum suspension setting – Open, Trail, or Lock - as you ride. You can adjust the suspension bias to toward a firmer or more open response via the SRAM AXS app or the left-hand bar-mounted rocker switch. The app also lets you adjust the low-speed compression and fine-tune the indexing on the wireless derailleur. For a deeper dive into this tech, see our full Flight Attendant review.
Flight Attendant aside, the Jeffsy is a decent climber for a mid-travel bike. The 77-degree seat tube angle (or 77.5 degrees if you switch the flip-chip around) keeps you well-positioned over the bottom bracket – unless things get really steep. The bike never felt overly long on the climbs and the front wheel didn't feel like it wanted to wander even on tight switchback turns.
Flight Attendant aside, the Jeffsy is a decent climber for a mid-travel bike. The 77-degree seat tube angle (or 77.5 degrees if you switch the flip-chip around) keeps you well-positioned over the bottom bracket – unless things get really steep. The bike never felt overly long on the climbs and the front wheel didn't feel like it wanted to wander even on tight switchback turns.
On descents the suspension tech is less useful though as it essentially stays open all of the time. But even without the faint whir of their Flight Attendant servos in action, the Rockshox Ultimate suspension with its 'buttercup' bumpers at the bottom ends of the fork damper and spring gives extra sensitivity to this well-balanced setup and the Lyrik/SuperDeluxe combo is an ideal choice for this breed of bike.
There's no noticeable freehub lag when engaging the pedals and the instant response from the excellent carbon wheels give the Jeffsy a really lively and capable character. The slick, cable-free shifts from the AXS electronic drivetrain are super rapid too.
Everywhere I rode, whatever the conditions, the Jeffsy gave me tons of capable control. Whether it was snake pits of writhing roots, blind leaps of faith, or plunges down ultra-steep faces, this confidence-inspiring ride encouraged me to hit everything as hard as I could.
Any gripes I have about the bike are very minor; I didn't really like the plastic-feeling rocker shifters at first, though they are more robust than they initially appear. The short and fairly wide back end (180mm at the widest point) caused me to occasionally clip my heel on the chainstay – YT has helpfully fitted clear frame tape to the outside face of the stay, but that has started to come away during testing. And while I did appreciate the lack of hydraulic hose, aside from a cleaner cockpit and the fact that it comes part of the electronic SRAM package, the benefits of the wireless AXS Reverb dropper are pretty minimal for me.
Verdict
While the YT Jeffsy Uncaged 6 is a fantastic riding machine on every level, whether a Flight Attendant equipped bike is worth the additional significant numbers it adds to the price will be down to you.
If you don't have the time or inclination for suspension fettling/faff and want to get a top of the line bike that's as easy to set up and ride as it gets, then you'll massively dig it. If you mostly do good old-fashioned mountain biking, i.e. big loops with just as much up and across as down, you'll dig it even more. However, if winch and plummet or bike park runs are more your type of thing, then you're unlikely to get the benefit of the subtleties of this top-notch tech.
If the latter applies, then the analog suspension of the Jeffsy Uncaged 8, will may well suit you better – as well as saving you a few thousand notes.
Test conditions
- Temperature: 10 to 30 degrees C and everything in between
- Conditions: Muddy and wet to dusty and bone dry
- Trails: Natural, steep, rooty, off-camber, trail center red loops and DH runs
Tech specs: YT Jeffsy Uncaged 6
- Price: $9,499 / £7,999 / €8,999
- Discipline: Trail/all-mountain
- Frame: YT UM carbon with flip-chip
- Head angle: 66/66.5 degrees
- Seat tube angle: 77/77.5 degrees
- BB height: 344/352mm
- Reach: 470mm (large tested)
- Fork: 150mm RockShox Lyrik Ultimate Flight Attendant, DebonAir + cartridge, AXS control
- Shock: 150mm RockShox SuperDeluxe Ultimate Flight Attendant, RCT 3 cartridge, AXS control
- Wheels: 29in Crankbrothers Enduro Carbon, front hub 110 x 15 mm, inner rim width 31.5mm, rear hub 148 x 12mm with Industry 9 Hydra freehub, inner rim width 29.5mm
- Tires: 29 x 2.5 Maxxis Minion DHF EXO 3C front, 29 x 2.4 Minion DHR II EXO 3C rear
- Drivetrain: SRAM XXI Eagle Flight Attendant crankset, XXI Eagle AXS derailleur, AXS Rocker Pedal shifter, XG 1295 Eagle 10-52 12-speed cassette
- Brakes: SRAM G2 Ultimate, 200m rotors f/r
- Seat post: RockShox Reverb AXS, 150mm travel (size large)
- Saddle: SDG Bel Air
- Bar and stem: 780mm Renthal Fat Bar Carbon 35, 50mm Renthal Apex 35
- Headset: Cane Creek Hellbender 70
- Sizes: S, M, L (tested), XL, XXL
- Weight: 30.8lb / 14kg (size large)
