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Jeffsy29 Core 4 CF

From$6,299

Claimed weight14.60 kg / 32.18 lb (avg for smallest size, tubeless, no pedals or bottle)Complete bike

FrameYT full-suspension frame…Fox 36 Float Factory, 29",…

GroupsetSRAM POD Ultimate Contr…SRAM X0 1295 Transmission…

WheelsDT Swiss EXC 1501 Splin…Maxxis Minion DHF, 29x2.50,…

Tire clearance61 mm

YT’s third-generation Jeffsy is a 29-inch-only all-mountain/trail bike that leans toward broad usability rather than a single discipline. Travel sits in the mid-pack at 145mm rear and a 150mm fork, and the frame sticks with YT’s V4L Horst-link layout. Carbon and aluminum frames are both offered, with carbon adding a STASH downtube compartment while both versions get accessory mounting under the top tube.

This generation is defined by practical refinement more than reinvention: easier service access and routing, more protection, and geometry updates that keep it current without chasing extremes. It’s aimed at riders who want one bike for regular trail rides that can still handle harder terrain and the occasional bike-park day, as long as you accept it isn’t an enduro-specific chassis.

YT Jeffsy

Build

Size

$6,299

02 / Specifications

Spec sheet.

Every component shipped with this build.

01Frameset

4 components

FrameYT full-suspension frame w/ YT STASH downtube storage

ForkFox 36 Float Factory, 29", 150mm, GRIP X2, 44mm offset, 15x110mm

Rear shockFox Float X Factory, 210x55mm, 2-position lever, custom tune (145mm travel)

Weight14.60 kg / 32.18 lb (avg for smallest size, tubeless, no pedals or bottle)

02Drivetrain & brakes

10 components

Shift leversSRAM POD Ultimate Controller, 12-speed

Rear derailleurSRAM X0 Eagle Transmission, 12-speed, T-Type

CassetteSRAM X0 1295 Transmission, 12-speed, 10-52T, T-Type

ChainSRAM Eagle Transmission (T-Type) 12-speed

CranksetSRAM X0 Eagle Transmission, 170mm, 32T, 2 guards, DUB

Bottom bracketSRAM DUB PressFit PF92 MTB Wide

Front brakeHayes Dominion A4 (Stealth black/grey)

Rear brakeHayes Dominion A4 (Stealth black/grey)

Front rotorSRAM HS2, 203mm

Rear rotorSRAM HS2, 203mm

03Wheels & tires

4 components

Front wheelDT Swiss EXC 1501 Spline One, 29", 30mm internal, 110x15mm, 6-bolt

Rear wheelDT Swiss EXC 1501 Spline One, 29", 30mm internal, 148x12mm, 240 Ratchet DEG 90, 6-bolt, XD

Front tireMaxxis Minion DHF, 29x2.50, EXO+ casing, 3C MaxxTerra, Tubeless Ready

Rear tireMaxxis Minion DHR II, 29x2.40, EXO+ casing, 3C MaxxTerra, Tubeless Ready

04Cockpit & contact

5 components

StemRenthal Apex 35, 50mm, 35mm clamp, +/-6°

HandlebarsRenthal Fatbar 35, 780mm width, 30mm rise, 7° backsweep, 5° upsweep

SaddleSDG Bel-Air 3.0 Overland (YT custom), 140mm, Lux-Alloy rails

SeatpostYT Postman V2, 31.6mm, MMX remote, adjustable drop (S:125mm / M:150mm / L:170mm / XL:200mm / XXL:230mm)

Grips/TapeODI Elite Motion V2.1 (lock-on)

03 / Geometry

Geometry & fit.

5 sizes published.

The Mk III’s fit is built around moderate reach numbers, a steep effective seat angle across the size run, and a front end that’s contemporary rather than ultra-slack. The seated posture is notably centered for a mid-travel bike, which is a big part of why multiple testers found it comfortable on long climbs and traverses without feeling overly upright. For riders who spend time grinding fireroads and then dropping into technical singletrack, it’s a position that keeps weight forward enough to manage front-wheel wander without forcing an aggressive, XC-like stance.

On the handling side, the geometry choices nudge the Jeffsy toward quick direction changes and strong cornering manners. Size-specific chainstay lengths aim to keep balance consistent as reach grows, though a couple of reviews still linked the shorter rear end (on S through L) to more lively behavior at higher speeds. The flip chip offers a subtle change in height and angles rather than a wholesale personality shift, so it’s more about fine-tuning pedal clearance and steering feel than transforming the bike.

Reach × Stack · size Mmm

Where the handlebar sits relative to the bottom bracket — the single most important fit pair.

01Fit geometry6 values

Stack620 mm

Reach455 mm

Top tube593 mm

Headtube length108 mm

Standover height728 mm

Seat tube length410 mm

02Component geometry5 values

Crank length170 mm

Handlebar width780 mm

Stem length50 mm

Saddle width140 mm

Dropper travel150 mm

03Handling geometry6 values

Headtube angle65°

Seat tube angle77.5°

BB height343 mm

BB drop33 mm

Wheelbase1214 mm

Chainstay length437 mm

Which size should I buy?

Slide your height to see the recommended size. GearWise's fit algorithm works from the published stack, reach, and ETT — the brand's own recommendation may differ.

Your height

5'8"173 cm

5'0"5'5"5'10"6'3"6'7"

Recommended sizeMBased on stack, reach & ETT for your height · score 95/100.

→Calculated from GearWise's own stack / reach / ETT algorithm — the brand's size chart may recommend a different size, and a proper bike fit beats any calculator.

04 / Other builds

The lineup.

6 builds, ranging $2,999 – $6,299.

The Jeffsy range is split into six completes across aluminum and carbon, with pricing running from roughly $3,000 to the mid-$6,000s in the US. Core 1 and Core 2 are aluminum, then carbon appears from Core 2 CF upward, with the carbon frame bringing the STASH downtube storage. All builds share the same wheel size and the same core travel format, so the riding differences are primarily down to suspension, drivetrain, and wheels.

At the entry point, Core 1 AL uses Marzocchi suspension, Shimano Deore shifting, and SRAM DB8 brakes with 200mm rotors, and it’s also the heaviest build listed. Core 2 (in both AL and CF) is the first big step in suspension with a Fox 36 Performance fork and Float X Performance shock, and it also brings higher-end brakes (Hayes Dominion A4) and DT Swiss wheels; it’s a meaningful jump if you care about damping quality and braking feel.

Core 3 steps into Transmission with SRAM’s T-Type drivetrain and moves to Crankbrothers Synthesis Enduro alloy wheels, while Core 4 CF goes further with Fox Factory suspension and SRAM X0 Transmission plus lighter wheels. Value calls in the reviews tend to cluster around Core 2 for riders who don’t need carbon storage, and Core 3/4 for those who want the carbon frame features and the cleaner, higher-end control from the drivetrain and suspension upgrades.

— · Currently viewing29 Core 4 CF

SRAM X0 Eagle Transmission

$6,299On this page

—29 Core 3 CF

SRAM S1000 Eagle Transmission

$5,299

—29 Core 3 AL

SRAM S1000 Eagle Transmission

Shimano Deore RD-M6100

$2,999

05 / Reviews

From the press.

21 reviews from the cycling press.

Across reviews, the Jeffsy Mk III tends to be described as easy to settle into, with a ride character that prioritizes calmness and traction over a hyperactive, ultra-pop feel. BikeRadar sums up the shift from prior versions as “calmer, faster and more composed” (BikeRadar), and Pinkbike frames the appeal around “easy and intuitive handling” (PinkBike). On mixed terrain, that translates to a bike that will do long climbs without feeling like a pure gravity tool, then carry speed and stay quiet when trails get rougher.

Suspension feel comes up repeatedly. MBR called it “pillowy” at the recommended 30% sag (Mountain Bike Rider), while The Radavist highlighted an “isolated” sensation at speed until tuning brought more feedback (Theradavist). Several testers noted that setup changes can meaningfully alter the bike’s character, and that the Jeffsy’s supportive tune helps it avoid wallowing even with a fairly active feel.

The main tradeoffs are familiar for this category. Weight is repeatedly mentioned, especially on higher-spec builds, and a few reviewers wanted more stability when pushing very steep or very fast trails. Off-road.cc found it could feel “skittish at speed” with the stock front-end numbers and short rear center (Off), and Singletrackworld fixated on the “65° head angle” as the limiter on steeper descents (Singletrackworld). Others, riding different terrain and setups, were less bothered, which is a hint that rider style and local trail speeds matter as much as the spec sheet.