YT Jeffsy Core 3 review

The YT Jeffsy Core 3 is the German brand’s 150mm-travel all-mountain 29er, aimed at the upper end of capabilities when it comes to the trail bike genre.

Though the frame hasn’t been updated since 2019, the Jeffsy’s then fairly radical shape means it still feels contemporary. It is also a previous Trail Bike of the Year winner – high praise indeed.

The landscape has changed in recent years, and so while the German direct-sales brand no longer represents exceptional value for money in the UK, this Core 3 model still packs a punch in the spec department.

When I first rode the Jeffsy I loved its easy-riding, fun demeanour, so how does it fare now, when put against the best trail bikes?

YT Jeffsy Core 3 frame and suspension

Carbon is used for the front and rear triangles on the Core 3. To ensure longevity, YT has added plenty of protection, from the replaceable down tube pad to the chainstays, and on the inside of the dropouts, too.

Furthering the frame’s durability are extra seals on the Horst-Link suspension’s pivots to keep mud and water at bay.

Should you wish to service the frame, all the pivots can be stripped from the non-driveside of the bike, save for the rear Horst pivot on the driveside. This is thanks to feedback from YT's DH team mechanics, back when the frame was being developed.

Cables run internally, with guided runs all the way through the frame, and a single clamping point as they exit near the base of the down tube, to help keep the bike quiet.

There’s not masses of room inside the front triangle, thanks to the shock’s location and the little rocker that pushes on the shock. However, YT has developed its own bottle, collaborating with Fidlock, to ensure you can carry plenty of fluid on the trail

The Horst-link suspension gives 150mm of travel at the back. YT says it's been designed to give plenty of pop for a fun ride on the trail – this is thanks to having ample mid-stroke support to push against.

Later in the stroke, the progressivity ramps up to prevent harsh bottom-outs, while the anti-squat has been designed to aid pedalling efficiency

YT Jeffsy Core 3 geometry

The geometry, though four years old, is still up to date, with a reach of 470mm on a large bike, paired with a 66.2-degree (measured) head angle in its low setting. This gives a wheelbase figure of 1,218mm.

A flip chip in the suspension linkage enables the bike to be steepened by 0.5 degrees, with the bottom bracket raising 8mm. The effective seat angle sits at 77.3 degrees in the low setting at my 750mm saddle height, still on-par with many more recently updated trail bikes.

YT offers the bike in five sizes, from S to XXL, with the brand suggesting riders in the range of 154cm to 202cm should be able to find a bike to match.

While the frame’s architecture, with its super-low slung top tube, looks as if has a tall seat tube, it is in fact relatively short at 435mm on a size large.

For the purpose of this review, I left the bike largely in its Low setting, because there’s little on the geometry chart to suggest this would be disadvantageous in most situations.

On technical climbs, the higher bottom bracket of the High setting might help, but I’d rather keep the bike set up with descending in mind.

YT Jeffsy Core 3 specifications

The Core 3 sits in the middle of the Jeffsy range. It comes with a spec list that shouldn’t need much alteration to get the absolute best out of the bike.

Fox supplies Performance Elite level suspension. At the front, there’s a 150mm-travel 36 fork, with the GRIP2 damper. Pressure-release valves on the back of the fork legs are there to improve sensitivity when dealing with altitude and temperature changes.

In the middle of the bike is a Float X shock, which comes with a small compression switch to further pedalling efficiency on smooth surfaces.

There’s a SRAM GX Eagle mechanical groupset, paired with basic G2 R brakes and 200mm rotors front and rear.

The bike rolls on Crankbrothers Synthesis alloy wheels. The rear is stiffer for improved reactions to pedal inputs, with a softer-built front wheel to improve grip and hand comfort.

The wheels are wrapped in Maxxis Minion DHRII tyres, in a 29x2.4in width. The lighter EXO casing is supplied at both ends.

e*thirteen provides the bulk of the finishing kit, though there’s a YT-branded Postman dropper post with 150mm of travel on a size large (S/M bikes get 125mm droppers, XL/XXL get 175mm posts).

This build represents a running update to the spec list, with the shock switched from the previously found DPX2 and the wheels replacing the DT Swiss M1900 wheelset.

YT Jeffsy Core 3 ride impressions

This bike was tested as part of our 2023 Bike of the Year test. It was compared to seven other leading trail bikes.

During testing, I took all the bikes to the same locations and trails for some dedicated back-to-back testing on a wide variety of terrain.

From hand-dug tracks in the woods to trail centre laps and BikePark Wales’ rocky runs, I ensured the trail bikes were exposed to every type of trail such a bike is likely to be ridden on.

Riding the bikes back to back, usually with four in each testing session, ensured I was able to pick out the finer performance points of each bike.

YT Jeffsy Core 3 climbing performance

With a 615mm top tube length and a seat angle I measured at around 77 degrees, the Jeffsy is a perfectly comfortable place to spend your time while grinding up a hill, especially because it comes with the SDG Bel Air 3.0 saddle – one of my favourite perches.

The seat angle is steep enough to put your hips over the cranks for an efficient feel. Yet it's not so steep that on flatter ground it feels awkward, or that you’re putting too much weight through your hands – especially when the suspension has sagged a touch.

While standing up and mashing on the pedals will induce a fair bit of pedal bob, if you’re sat spinning, the rear shock remains relatively static.

On steeper drags when you’re putting a bit more effort into your climb, it starts to oscillate with your pedalling. As such, while it’s not an inefficient bike to climb on, it’s perhaps not the most peppy uphill. On smooth surfaces, I made use of the easily accessible lockout switch on the Fox Float X shock.

When surfaces got a bit more marginal, the early-stroke suppleness that gives a hint of bob helps the rear tyre dig in and grip. When you come across a root or rock step, the suspension feels free to soak up the edge and generate traction.

The pair of Minion DHRII tyres from Maxxis roll well. Thanks to their lightweight EXO casing, they don’t add as much rotating weight (and thus perceived sluggishness) as weightier tyres might.

The SRAM GX Eagle drivetrain shifts nicely under power, and the 32:52 bottom-gear ratio is more than low enough to deal with most regular climbing requirements.

YT Jeffsy Core 3 descending performance

The Jeffsy is one of those bikes that’s really easy to jump on and ride, without needing any major recalibrations of your riding style.

I was immediately in tune with how the bike felt, enabling me to rip familiar trails as soon as I swung a leg over it.

This is likely thanks to its middle-of-the-road geometry and comfortable suspension feel.

It’s the kind of bike where it feels as if you’re up to speed within just a few pedal strokes – even if, under power, the rear suspension robs a bit of juice through bobbing.

Once you are up to speed, pumping the bike down to its supportive low-mid-stroke is an effective way of maintaining or gaining pace.

The tyres zip along nicely thanks to their low weight, but their thin casing is a bit more pingy when rattling over rocks and roots than a heavier-casing tyre.

This makes the bike feel a little more unsettled over rock gardens than a better-damped tyre might. They’re also more puncture-prone than I’d like on a bike with this much travel.

The suspension units, front and rear, work really well on descents.

It’d be hard to separate the Performance Elite level kit from the pricier Factory dampers, if you couldn’t see the lack of the gold Kashima coating.

It feels as though the GRIP2 damper is a touch more forgiving than it originally was, so I ran a couple of clicks (from open) of low-speed compression damping, to help keep the front end of the bike propped up.

The shock is another top-performer, with a smooth and controlled feel, and ample adjustment to get it riding right.

The rear suspension has that lovely soft, supple feeling early in its stroke, isolating the bike from the majority of trail chatter, smoothing the way so you can concentrate on the trail ahead.

It’s also effective under braking, keeping the rear wheel glued to the ground and letting the Minion DHR II do its job as best it can. This, along with the clamped cable guides and effective chainslap protection, makes it a seriously quiet bike to ride.

There’s the previously mentioned support later in the stroke, which keeps the bike from getting overawed by repeated big hits. It enables you to pump the bike through the terrain, generating either speed or plenty of pop.

This contributes to the Jeffsy having a lively, fun attitude to the trail you’re on. It appears happy to be muscled around and thrown off lips, excelling when the rear wheel steps out of line.

Faced with the rougher, rockier tracks of BikePark Wales, or steep rooty tech, the Jeffsy didn’t quite have the same assured feel as some of the calmer, longer bikes in this Bike of the Year test.

It doesn’t quite get bucked around, and I preferred picking a smooth line or jumping over terrain, rather than straight-up ploughing through it.

These trails highlighted another area in which I feel the Jeffsy could be improved.

The 35mm-diameter bars, and the grips, which feel as if they’re the result of the bars being dipped in a bucket of liquid rubber and drip-dried, are harsh.

This is despite the best efforts of the Crankbrothers Synthesis wheels. These, in our testing, have proved to be comfortable and accurate wheels – but they can’t quite mask the rigid-feeling cockpit.

In terms of spec, the 435mm seat tube is pretty short for a large-sized bike, so I’d have liked a longer dropper post to have been fitted.

The size-large bike gets a 150mm post, while the XL and XXL get 175mm. It definitely feels as though there’d be room for this longer post to be fitted, and it was one of the few bikes in this test where I felt the dropped saddle height compromised how I felt on the bike on steep tracks.

I’d also like to see the bike with better brakes. SRAM’s G2 R brakes are pretty basic, and not the punchiest stoppers around, even with the 200mm rotors attached to both hoops.

How does the YT Jeffsy Core 3 compare to the Trek Fuel EX 8?

Both the Jeffsy and the Fuel EX are sorted trail bikes with a nod towards the gnarlier end of trail riding.

The Trek perhaps has a calmer ride over the roughest tracks – it’s pretty unflappable. While the Jeffsy doesn’t throw its toys out of the pram, the Fuel EX seemed to deal with fast, rough tracks a touch better.

Both bikes are adept at mellow terrain too, with the Fuel EX being more pert under power. Of the two, it’s the Jeffsy that likes to hussle around the trees and fling itself into the air a little more.

Both suffer from relatively harsh front ends, but the Trek is the least comfortable of the two, thanks to a seriously stout chassis – both have skinny grips and 35mm-diameter bars, though.

The Jeffsy undoubtedly wins in the value stakes.

YT Jeffsy Core 3 bottom line

Though the oldest contender in Trail Bike of the Year, YT hasn’t been left behind with the Jeffsy Core 3. Its shape is still up to date, and the quality of the suspension dampers is evident.

It’s a super-fun and easy bike to ride, and one which consistently brought a grin to my face.

I might not pick it for the gnarliest days out, but as a do-it-all bike, it ticks a lot of boxes, and is great value to boot.