YT JEFFSY 29 CORE 4 REVIEW

THE DIRT
YT has begun to roll out some brick-and-mortar sites in key locations worldwide (currently Germany, UK and USA), which they call the YT Mills. These feature large showrooms that allow prospective customers to have a look at the YT range up close and personal and are manned by knowledgeable staff who are enthusiastic about their bikes and make killer coffee. I visited their UK mill in the Surrey Hills to collect my Jeffsy test bike, and after a comprehensive tour of their impressive facility I was given the treatment, a typical customer would receive when picking up a YT bike of their own in-store. Suspension pressures, saddle height and cockpit setup were all performed with the help of the kind employees, so I was ready to roll in no time. This is a valuable step in the right direction to removing some of that “alien” direct sales feeling, having a much more direct line of communication than the typical delayed email response from YT HQ you may have faced when purchasing one of their bikes previously. Another significant benefit of these YT Mills are the spare parts and warranty aspect, where YT are pushing hard to ensure that customers are taken care of much more effectively and efficiently than before.

Once this initial ballpark setup was out the way, it was time to hit the trails around their UK Mill – the famed Surrey Hills that can claim to have produced some of the world’s best mountain bikers including Brendog, Bernard Kerr and Olly Wilkins to name a few. This huge area of woodlands is littered with local-built trails and provides a great location to get familiar with the handling of a bike with a bit of everything from flat out jump tracks through to steep rutted turns. I hopped on the Jeffsy and instantly felt pretty comfortable trying to keep up with the YT employees, but there were a few things most definitely amiss with the setup that I managed to resolve over the course of the testing period. Most notable were the suspension setup and tire pressures, which were certainly on the “safe” side of things. This was the first bike I’d used my Motion Instruments data acquisition system on, and as such I was able to obtain a more detailed and optimized suspension setup than ever before. Further testing led to an increase in air pressure on both ends, a significant increase in rebound speeds and a healthy drop in tire pressures once the flimsy casings were addressed. The result was 28% sag out back with the stock volume spacers paired with 20% up front, providing a good compromise of dynamic ride height. Though there were big changes required to get the most speed and grip out of the bike for me, the initial setup had proved perfectly rideable and the kind of setup anyone could hop on and ride easily, which is absolutely the correct approach.

The remainder of the test period saw the Jeffsy subjected to my typical mixed bag of riding, from downhill laps at Revolution Bike Park through to mellow mile crunching and everything in between, which the Jeffsy took in its stride. The climbing position is very comfortable, with what is now a relatively average seat angle sticking a good balance of front wheel weighting without feeling bolt-upright and too compact. Under power there’s a fine balance of support and compliance, with a subtle amount of bob that doesn’t reach the energy-sapping feeling, but enough movement allowed in the rear end to conform to the terrain below. I’d still tend to flick on that compression switch for the smoother climbs, but it wasn’t a necessity and made technical climbs a very pleasant experience. Overall bike weight is not super light but equally not too portly, falling into a happy middle ground where you’re not scared to climb or send. The “steep” head angle lets the Jeffsy maneuver well in the slower switchbacks, with the mid-length rear end maintaining a good halfway house of front wheel weighting without losing the all-important grip. Climbing the Jeffsy is damn good.

Much to my surprise, there’s a healthy amount of grip and sensitivity on offer that pushes the descending ride feel more towards the enduro side of the spectrum than I’d been expecting. This does lead to the Jeffsy feeling a touch more cumbersome when pumping through mellower terrain than other similar bikes as it is more eager to use that first half of its travel. However, it does lead to an impressively capable package when it comes to Enduro bike terrain, where both ends do a great job at suggesting there’s more than 150mm travel on offer and manage to avoid hang-up reasonably well over square edge impacts. This extends to the bigger hits, with high levels of progression requiring a serious compression before the bottom out bumper comes into play. It’s not to the extent that it’s the ultimate Enduro race machine, but it could likely handle all but the gnarliest races without too much of a complaint. This initial stroke sensitivity means it’s not the poppiest machine out there, but with a little more effort its relatively light weight will soar and let you make use of that progressive travel when it comes back down to ground.

Geometry-wise, the Jeffsy feels quite poised on faster and flatter tracks, but that steep head angle can find its limits in the steeper switchbacks, with less steering confidence and an increased tendency to “tuck”. The flip side is the impressive ability to navigate the flat and tight turns, with less rider input required and the ability to change direction on a dime. I’d suggest the Jeffsy to be a great candidate for a bit of overforking to unlock a little extra confidence in the steeps – a 10mm longer fork combined with slightly more dynamic sag on the rear in the low geometry setting would lead to a slacker head angle without compromising the BB height and pedaling position too much, and I think it could push the Jeffsy towards an all-round “light enduro” destroyer if that’s what you’re looking for. This isn’t to say it’s incapable of riding steep terrain in its stock guise, only that slacker competitors tend to offer a touch more safety and confidence. I’d place the stiffness of the Jeffsy frame in the upper half of the scale for sure, but it’s not at the extent of deflecting everywhere or becoming hard to handle, only reassuringly sturdy.

What isn’t so sturdy is the tire spec. Although they could make sense for some customers, they’d be the first item I would swap out in order to add some extra capability to the bike at the expense of a little agility. Sram’s G2 brake surprised me with its performance, however, did begin to show its lack of ultimate stopping power for my 210lb kitted mass once the going got extra steep or the braking became sustained. Otherwise, there’s little left to be desired from the parts spec on the Core 4, with the remainder performing excellently. A particular relief in the parts spec is the 36t driver in the DT Swiss rear hub, which halves the slack from the DT hubs of the past and makes for a much more pleasant experience on technical climbs. Though the pricing is still reasonable compared to some brands, YT has begun to lose their insane spec offered at each price tag, however their frame quality has come on leaps and bounds at the same time so I’d suggest it’s not a case of greed.

The Wolf’s Last Word

The YT Jeffsy Core 4 29er may not be the newest model on the scene, but still holds its own as a versatile all mountain bike that’ll happily crunch out mellower miles or tackle some tough enduro tracks. With a surprisingly sensitive and “bottomless” suspension feel, dialed parts spec (apart from flimsy tires) and good pedaling manners there’s a lot going for the Jeffsy, so long as you’re not looking for the ultimate steep terrain crusher.

Price: £4,649 /€5,199 /$5,199
Weight: 14.35kg/31.6lbs (XL, actual, no pedals)
Website: YT-Industries.com

SPECIFICATIONS

CHASSIS
Frame: Carbon | 150mm
Fork: Fox 36 Float | Factory | Grip 2 | Boost | 150mm
Shock: Fox Float DPX2 | Factory | 3-pos | 210×55

COCKPIT
Brakes: SRAM G2 RSC | 200mm
Shifter: SRAM X01 Eagle | 12s
Stem: Renthal Apex | 35 x 50mm
Handlebar: Renthal Fatbar | 30R x 800W | 35mm
Headset: Acros | ZS44/ZS56
Saddle: SDG Bel Air 3.0
Seatpost: YT Postman | 125 mm (S-M) | 150 mm (L) | 170 mm (XL-XXL)

WHEELS
Wheelset: DT Swiss XM1700 Spline | 30mm | 110/148 | XD | 36SL
Front tire: Maxxis Minion DHR2 | 29“ x 2.4 | EXO Casing | Tubeless Ready | 3C MaxxGrip
Rear tire: Maxxis Minion DHR2 | 29“ x 2.4 | EXO+ Casing | Tubeless Ready | 3C MaxxTerra

DRIVETRAIN
Bottom Bracket: SRAM Dub pressfit
Cassette: SRAM XG 1295 | 12s | 10-52T
Cranks: SRAM Descendant Carbon | DUB | 32T | 175mm
Derailleur: SRAM X01 Eagle | 12s