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The YT Jeffsy 29 Core 3 is a very capable all-mountain bike which can handle the rough stuff but is equally at home on flow trails and jumps. While the specification list is solid for the money, it's worth paying extra attention to frame sizing and geometry to get the ride you want. With a longer dropper and some tougher tyres this bike has what it takes to be a real challenger when it comes to the best mountain bikes. 

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YT Industries Jeffsy 29 Core 3 - Technical details

The Jeffsy is YT's all mountain offering. With a 150mm of front and rear suspension travel, it sits between the enduro-orientated Capra and the short-travel Izzo. This is offered with a full carbon frame except for the Core 2 model. 

YT has nailed the set-up experience to get you rolling as quickly as possible and with the YT Mill there is even UK support when needed. The Jeffsy proves to be a fun and playful affair at a price point which is hard to ignore. 

The Jeffsy is available in the base model alloy framed Core 2 retailing at £3,000 from the UK YT website. The Core 3 and Core 4 variants are carbon framed and better specced but jump up to £4,200 and £5,200, respectively. The Uncaged variants represent the “best of the best” and are specced with Cane Creek suspension for the Uncaged 8 (£5,200) and the Uncaged 6 (£8,800), currently equipped with RockShox flight attendant suspension.

YT Industries Jeffsy 29 Core 3 - Frame details

The Jeffsy frame comes with a host of neat features. Internal cable routing gives a clean look, using internal tubes to make cable fitting easy and stop unwanted noise from rattling cables. A bolt-on plastic shield protects the down-tube from rock strikes and rubber guards in the rear triangle quieten chain slap. A flip-chip down in the shock mount gives a high and low setting which changes the head- and seat angle by 0.5-degrees, the BB is also affected by 6mm.

YT use its virtual four-link (V4L) suspension layout on the Jeffsy to deliver 150mm of travel. YT says there is a “high amount” of anti-squat which keeps the rear suspension neutral and improves pedal efficiency but more on this later…

With water bottles being a major requirement for most riders, YT’s suspension design has caused problems in the past. This has been addressed with YT’s proprietary Thirstmaster bottles using a Fidlock connection. As an optional extra, the Jeffsy will hold the Thirstmaster 4000 which can be purchased for £45 from the YT Mill (in person or via email/phone) and holds 600ml.

YT Industries Jeffsy 29 Core 3 - Sizing and geometry

YT offers the Jeffsy in five sizes from small up to extra extra large, using a size guide this caters for riders from 154cm through to 202cm. At 183cm (6ft) I fit slap-bang in the middle of the L and XL size which presents a tough decision. The L is on the small side and therefore will be more of a fun, playful and nimble ride whereas sizing up to the XL will give a more stable ride. Based on the Jeffsy’s trail orientation, I went for the more playful size L.

The reach is my usual go-to number to determine how a bike will fit me, with the Jeffsy measuring 430mm for the S and increasing in 20mm increments up to 510mm for the XXL. The Large pictured here sits at 470mm, which is a little on the conservative side compared to other brands.

The 66-degree head angle (in low) is also fairly steep compared to the latest numbers seen on other bikes, this will add to a nimble feeling of the bike but will most likely feel less stable on the steep sections. The short chainstays also add to this with S-L getting 435mm and 440mm for XL-XXL.

The seat angle is reassuringly up to date, 77-degrees (in low), which gives a comfortable climbing position.

YT Industries Jeffsy 29 Core 3 - Specification

The Core 3 on test represents solid spec for the money. Drivetrain duties are handled with the staple SRAM GX 12-speed setup, which gives plenty of range to climb and descend.

SRAM also has the brakes covered with a set of G2R, sporting 200mm discs front and rear. YT has kitted its own branded dropper, the “Postman” which offers 150mm of drop in the Large size. The XL and XXL get 170mm, while the S and M get 125mm.

The 150mm Fox 36 fork is burly enough to handle some serious abuse and thanks to the Performance Elite flavouring, there is more than enough adjustment to get it working exactly as needed. The matching Fox DPX2 shock also comes in the Performance Elite guise with a lock-out lever for the climbs.

The DT Swiss M1900 wheels are not the lightest but they're sturdy and shod with Maxxis DHRII front and rear, complete with EXO casings. The wheels are tubed from the factory but YT has the wheels already taped and include tubeless valves so going tubeless is mega-simple.

YT Industries Jeffsy 29 Core 3 - Setup

The bike comes mostly assembled out of the box and includes a tool pack to get you going. The tool pack features a shock pump, an 8mm Allen key for the pedals and a torque wrench with attachments. Basically, all you need is a track pump for the tyres and you’ll be ready to shred.  

YT has provided an online guide for setting up your suspension. After entering bike and weight details you’ll get a step-by-step guide on air pressures and dial settings which serves as a baseline. Of course, this is only a guide but it’s a brilliant place to start when you’re on a fresh bike.

For my setup, I raised the stem and fitted some fatter grips based on personal preference. The suspension setup was close but I added some more air in the rear and more low-speed compression to keep the front a little higher on the climbs. After just two rides, my setup was dialled.

YT Industries Jeffsy 29 Core 3 - Performance

I have to admit I pre-judged the Jeffsy before looking at the geo numbers. I figured its short chainstays and a slack seat angle would make it a handful to climb but I was pleasantly surprised. The 77-degree seat angle (in the low setting) is by no means slack and gives a stable seated position. Although the chainstays are short at 435mm, they do not seem to hinder the climbing ability. I’ve been amazed at how comfortably I've been able to pedal up steep climbs. With the head angle being on the steeper side, I’ve had no issues with slow-speed manoeuvring and can place the front wheel confidently while on the ups.

The rear shock is fitted with a lock-out lever which I have used on occasion. The V4L suspension layout gives a stable platform once into the sag but is quite active in the first ~30% of travel. This is handy while descending but we’ll get to that. Setting up with the recommended compression settings, the rear end felt well controlled while climbing.  

If you imagine a sliding scale between long/stable bike and a nimble/playful bike, the Jeffsy falls towards the latter. The steeper head angle, short chainstays and shorter reach result in a bike that wants to pop and jive down a trail. This results in a fun bike that can be placed anywhere on the trail and really make the most of ripping round tight corners and float jumps.

When it gets steep or fast the head angle does let the Jeffsy down - a degree or more slacker would add to the stability and handling confidence. That's not to say the bike lacks confidence - oh no. The 36 fork is more than capable enough to handle some real hits. I’ve been impressed at how much abuse a stout 150mm fork can handle. The Jeffsy frame is plenty stiff enough to keep up with the fork, and the V4L suspension gives traction and support as required.

The spec held up well, even when on the charge. If you regularly ride steep trails with big compressions or sharp rocks I’d recommend upgrading the EXO tyres to something with thicker casings. Less likely but some heavier riders may also want to upgrade the brakes. The SRAM G2s have sensible power but some Codes would really help scrub off speed with ease. 

I was pleasantly surprised at how quiet the bike is. There's no cable rattle or chain slap. The only noise comes from the Thirstmaster bottle when it's full. I guess 600ml of water is a fair amount to restrain but the rattle stops after a couple of mouthfuls have been consumed.

My biggest gripe with the descending comes from the dropper post. The 150mm of drop simply is not enough. I found myself loosening the seat clamp and physically pushing the post further into the frame when I knew trails were getting rowdy for fear of being rear ended by my seat. Fortunately, this is easily fixed with an upgrade but annoying that YT didn’t spec a longer dropper. For riders who are on the shorter end of the large sizing spectrum, it might be worth upsizing to a longer dropper. At 6ft tall, I had approx 90mm stick out of the seat tube.

YT Industries Jeffsy 29 Core 3 - Verdict

The YT Jeffsy Core 3 comes in at £4,200 from the UK YT website. It's no doubt that with a carbon frame, high-level suspension and GX drivetrain this is a good deal although perhaps not as outrageously good value as YT bikes of yesteryear. If you’re in this market we can’t ignore the Canyon Spectral, the closest direct-sell comparison to the Jeffsy. Liam reviewed the Spectral CF8. The Canyon wins marginally on spec with a slightly improved wheelset and uses a Shimano drivetrain rather than SRAM. I’d argue the geometry is a little more up to date on the Canyon as well with a longer reach and slacker head angle. The seat angle is noticeably steeper on the Jeffsy so it’ll climb better and the YT presence in the UK will put riders' minds at ease should there be any issues. There's not much to tell them apart really.

Another option, which is perhaps a bit left field is the Focus Jam 6.0 LTD. At off.road.cc we haven’t had the chance to swing a leg over one of these but, on paper, it looks like it's worth a look-in The geometry is similar to the Spectral and the spec is killer. At £4,200 for RockShox Ultimate suspension and SRAM GX AXS drivetrain, this could be an absolute steal. The downside is the frame is alloy rather than carbon and therefore is quite a bit heavier.

The YT Jeffsy Core 3 represents a solid bike for the money. The carbon frame, decent spec and sensible price tag make this a strong contender in the best trail bike category. The fun-and-nimble nature of this bike makes it a real joy to take down a twisty and undulating trail while the up-to-date seat angle means it has no problem getting back to the top.

The YT support to get you up and running is impressive, everything bar a track pump is provided and the suspension set-up guide is as good as it gets. There are, of course, a couple of gripes - the biggest being the seat post length and tyres, the latter of which could have thicker casings depending on the terrain you ride. I’d argue some of the geometry is a little out of date but it very much depends on what you’re looking for in a bike – the Jeffsy certainly is a firm favourite in my opinion.

• www.yt-industries.com

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