YT’s JEFFSY trail MTB has received some updated build specs for 2025. The JEFFSY CORE range’s four build options have been revised and now include carbon or aluminum frame options for the mid-spec models. The highest-end model sticks with a carbon frame and the entry-level bike is available in aluminum only.
YT now equips the JEFFSYs with Hayes Dominion A4 disc brakes on all but the base model, options for SRAM T-Type drivetrains, and carbon wheels on the highest-end CORE 4 bike.
YT JEFFSY Key Specs:
The JEFFSY is a trail-focused MTB, designed to offer balanced capabilities on both climbs and descents. This mid-travel rig offers 145mms of rear travel, controlled by YT’s V4L linkage. 150mm forks are stocked on all models, but the frame can run a 160mm fork. The JEFFSY CORE bikes roll on 29” wheels, and YT makes no mention of MX compatibility for these models.
The latest JEFFSY carbon frames include STASH downtube storage, plus an accessory mount on the underside of the top tube. The compartment’s storage lid is double-sealed for water resistance and to keep things quiet. Aluminum models do not get in-frame storage, but they do include the top tube accessory mount for on-bike tools.
As for fitments the JEFFSY frame offers UDH derailleur hangers and runs Boost 148mm rear axles. Bottom brackets are PF92 on carbon frames, while the aluminum models use BSA threaded BBs.
A range of 125-230mm dropper posts are stocked between the different frame sizes (except the CORE 1 which tops out at a 200mm post). All models get YT’s Postman V2 dropper post with adjustable travel and a 31.6mm diameter.
All JEFFSY frames feature a water bottle mount on the down tube just above the BB. This mount can host YT’s 620ml Thirstmaster 6000 bottle with its side-loading cage. Both carbon and aluminum frames feature internal cable routing through the front triangle, plus chainstay and lower down tube protectors.
Geometry:
JEFFSY frames are available in five sizes from small to XXL. This range should cover riders from 5’0” to 6’8”. A flip-chip in the frame offers High and Low geometry settings… check out the chart to see the differences between the two settings and all figures not highlighted below.
In the High position, the JEFFSY has a 65.6° head angle. The seat mast angles range from 77.5 – 79.2° depending on frame size. In Low, the steering angle drops to 65° and the seat masts slack out to between 76.9 – 78.6°. Reach numbers are not pushing boundaries, with a medium frame coming in at 455mm (Low) or 462mm (High) and a large measuring 475/481mm.
YT offers two different chainstay lengths across the size range. S-M-L frames get rear ends measuring 435mm (High) or 437mm (Low). L-XXL frames get 440mm (High) or 442mm (Low) chainstays.
Model Lineup:
For complete build specs on each model check out YT’s website. Below is a quick highlight of the JEFFSY CORE lineup’s build specs.
JEFFSY CORE 4 CF: $5999
The CORE 4 CF is the highest-end JEFFSY model, and it is only offered with an ultra-modulus carbon frame. This bike gets FOX Factory suspension, with a 36 GRIP X2 fork and Float X rear shock. The CORE 4 rolls on DT Swiss’ EXC1501 Spline wheels with carbon rims and 240 hubs.
This top-end model also gets a SRAM X0 T-Type transmission, Hayes Dominion A4 brakes, and a YT-exclusive Renthal Apex stem and Fatbar handlebar. Weight for the CORE 4 model is listed at 32.18lbs. It is available in Fog Green or Black Magic Bolt colorways.
JEFFSY CORE 3: $4999 (CF) or $4499 (AL)
The JEFFSY CORE 3 is available with either a carbon (CF) or aluminum (AL) frame. Some key components on the CORE 3 include RockShox suspension, with a Lyrik Ultimate Charger 3.1 fork and Super Deluxe rear shock. This model offers a SRAM S1000 T-Type transmission.
The CORE 3s come with Crankbrothers Synthesis Enduro 2 aluminum wheelsets, Hayes Dominion A4brakes, and the same YT exclusive Renthal Apex stem and Fatbar handlebar as the CORE 4 model. Frame color options (carbon or aluminum) are Concrete Grey or Black Magic.
JEFFSY CORE 2: $3999 (CF) or $3499 (AL)
Also available with a carbon or aluminum frame, the JEFFSY CORE 2 comes equipped with a Fox Performance suspension package. Up front is a 36 Float fork, and out back is a Float X rear shock. Driving the CORE 2 is a Shimano SLX drivetrain with an XT shifter.
You still get the Hayes Dominion A4 brakes (on 200mm rotors) on this model, reeling in its DT Swiss E1900 wheelset. The cockpit includes YT’s own handlebar and a Race Face stem. Color options for carbon frames are Mud Green or Black Magic Bolt. Aluminum frames come in Frost Blue or Black Magic.
JEFFSY CORE 1 AL: $2799
The entry-level JEFFSY CORE 1 is available with an aluminum frame only. This bike gets Marzocchi suspension, with a Bomber Z1 fork and Bomber Air rear shock. Gearing is provided by a Shimano Deore drivetrain, while SRAM handles braking with their DB8 mineral oil brakes.
The CORE 1 bike also runs Sun Ringle wheels and YT cockpit components. Frame color choices for this model are Drip Yellow or Black Magic. YT lists the CORE 1’s weight at 36.37lbs.
The new JEFFSY CORE range is available for purchase now. Shipping for various models/sizes/colors is expected between March and April in most cases, with some options still TBD.
