Need to know

• Latest Jeffsy Core 5 has 145mm travel and a 150mm fork, with Fox Factory suspension
• Core 5 model is top of the range, comes with SRAM XO AXS T-Type drivetrain and a £5,999 pricetag
• Downtube internal storage now as standard on the Ultra Modulus carbon fibre bike
• Steeper 78º seat tube angle and a better pedalling response tweak the bike’s attitude
• YT has added more progression to the shock, and added more anti-squat to help Jeffsy climb

YT has distanced the new Jeffsy Core 5 from the Capra enduro bike, but it still rips the descents far better than a trail bike has any right to

The Jeffsy Core 5 is easily the most high-tech bike YT has ever made (e-bikes aside). From the High Modulus carbon fibre frame now with downtube storage, to the latest SRAM T-type electronic shifting, the brand has spared no expense.

And therein lies the problem, has YT stepped beyond its mantle as a sensibly priced provider of excellent bikes? Can it still lay claim to being one of the best trail bikes on the market today?

The silhouette may barely have changed from the old bike, but the latest Jeffsy gets a host of updates, including a gear mount under the top tube

YT Jeffsy third generation

Enough questions for now, the details are that the new third generation Jeffsy now comes with 145mm travel, making it 5mm shorter in travel than the outgoing bike. Didn’t see that coming. This applies to all bikes in the range, which you can check out in full on our full news story and Jeffsy range breakdown.

The seat stays drive the shock directly, with a geo adjust flip chip mounted on the lower shock mount, and there’s still space for a 620ml bottle

Why take 5mm off the bike’s travel? One answer is to better differentiate the Jeffsy from its big brother the Capra, an enduro bike with 165mm travel in its full 29er build. This fits in nicely with the new frame design too, YT hasn’t tried to make the bike burlier, stiffer and heavier as so many trail bikes seem to have become over the years. The temptation to add the brand’s Side Wing – an asymmetrical strut between the downtube and seat stay – must have been hard to resist.

Instead YT has put its efforts into making the Jeffsy a better climber, at least on paper. The brand’s suspension engineers have “adjusted” the anti squat characteristics for better climbing traction and acceleration, which can only really mean that they’ve increased it. YT has also added more progression to the shock tune, which should be handy when you’re really hauling, sending the bike off drops or thundering down enduro tracks. That means not only is there less suspension to play with, it’s also harder to access and in theory you’ll spend less time way down at the bottom of the stroke.

Beneath the mud the frame is sleeker and better looking, while in practical terms the bike puts you in a better position to pedal

Jeffsy frame 

The new Jeffsy doesn’t look remarkably different in silhouette from the old generation bike, there’s still a four-bar linkage design, with the shock driven directly by the seatstays, rather than connected with a yoke (as on the Capra). In fact the only discernible difference is the missing bridge between seat tube and top tube, in its place you get a chunky section of carbon that looks more modern. Aesthetically it’s cleaner, simpler, and the new lines around the head tube somehow slicker.

YT’s in-frame storage is well designed, but the 110x50mm door could do with being longer to more easily access the contents therein

Breaking into a crucial piece of frame architecture, like the downtube, and leaving a hole there for storage is not an easy thing to do. It needs careful CAD to work out how to manage the stresses a bike undergoes and where to add extra material. The bigger the door, the easier it is to stash stuff inside, but the harder it is to make the bike strong. YT’s isn’t as useful in size as those from Specialized or Trek, but the door catch is very cool and the whole thing is watertight, rattle free and inside it comes with two tool wraps to stash your adjustable spanners and so forth.

Semi-proportional geometry: YT makes two differently sized back ends, a long version for XL and XXL bikes, and a 5mm shorter one for smaller sizes

Bigger sizing and geometry

It had to happen really, YT’s bikes haven’t been the most generous in terms of sizing in recent iterations. But the Jeffsy looks set to change that. I rode a size XL at the launch, with a claimed reach measurement of 495mm, meaning YT has added around 20mm to the bike’s length. That’s a good size order change there, while the low slung top tube, good standover height and shortish headtube mean you could easily choose between two sizes.

YT has also steepened up the seat tube angle, and in fact each size gets a specific angle to maintain an effective 78º across all sizes, at the correct proper saddle height. YT has also kept two different chainstay lengths across the sizes, the XL and XXL bikes benefitting from 5mm more room.

The Jeffsy comes with plenty of protection, on the downtube and driveside chainstay, and a double bashguard on the crankset

How the YT Jeffsy Core 5 rides

The Core 5 Jeffsy is top of the range and as such you get the best components. SRAM’s latest T-type drivetrain in XO format powers the bike, which is reportedly excellent in every way, from reliability to shifting performance. This isn’t my experience though, I found it noisy in muddy conditions and by the end of my first day riding the Jeffsy I’d snapped the chain. Perhaps there was a factory fault on my drivetrain, as we’ve previously tested SRAM Transmission and rated it as outstandingly reliable. 

YT’s tyre choice is smart, the Maxxis Minion with MaxxTerra compound up front can’t match an Assegai for out and out grip but it’s predictable and there’s good edge bite. Besides, this is a trail bike and compromises have to be made, this time it’s for rolling speed over traction. 

We’ve long bemoaned the cheaper dual compound tyres and thin casing tyres YT seems to favour, so it’s great to see the new bike equipped with the latest EXO+ casing tyres too. Offering more protection than the old EXO, Maxxis has reduced the TPI count down to 60 from 120, and added a butyl insert at the bead. Maxxis says this gives it twice the tread and sidewall puncture protection, and a 20% protection increase from pinch flats. 

The Jeffsy feels well balanced, and with supple suspension you pick your line

There’s a suppleness to the Jeffsy suspension, it dips into its travel with ease and you definitely access all 145mm of available travel. YT’s advice is to set your sag at 30%, which is deeper into the travel than most trail bikes I’ve ridden, but it’s probably one of the reasons for the pillowy feel. If you’re setting up the bike at the YT Mill in Surrey you’ll get help with that, but if you’re receiving the bike by post that 30% sag equates to 16mm on the shock shaft.

Yet despite the soft suspension setup it doesn’t bounce off the bottom out bumper, and I wasn’t wallowing about at the bottom of the stroke. I didn’t bottom out the bike, even on the roughest Cwmcarn off-piste tracks, and my new pedals managed to keep all their pins. No pedal bonking for me then. And while you can definitely reach the limits of the Jeffsy’s travel it still feels closer in character to an enduro bike, despite all the changes. How much of this is down to the brilliant Fox Factory shock and fork is hard to say, but what I can report is that YT has the tune and the fore and aft balance of the bike spot on.

The Jeffsy proved a playful bike, as well as having composure in techie sections

Does it pedal better than the old bike then? In a word, yes, the Jeffsy is better to sit down and pedal up the hills and this could be as simple as the steeper seat angle putting me into a more effective position. I think there’s more going on though, out of the saddle the bike feels more urgent and cranks up to speed more quickly than I remember. That makes it more effective as a trail bike then, which needs to work just as well on mellow flowy trails as it does on the rowdy descents. 

Dropping the bar height by 5mm with a headset spacer made a huge difference to finding front wheel grip

We do need to talk about price because YT made its reputation delivering amazing value bikes. I believe the Core 5 continues that trend, and while nearly £6,000 for a bike is still crazy money for plenty of us, when you compare it to the competition it’s actually great value. Where else can you get a carbon fibre bike with internal storage, adjustable geometry, SRAM’s XO T-type drivetrain, Fox Factory suspension, and size-specific chainstays? Let us know on the socials if you think we’ve missed something.

I’ve only one gripe with the pricing, it’s that YT charges £5,999 for the bike in the UK, and €5,999 on the continent. The exchange rate is not 1:1 and that means it’s either overpriced here or underpriced there.