Jeffsy Primus 26
A 26″ aluminum frame mountain youth bike with upper mid-range components and hydraulic disc brakes.
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Manufacturer Price
$1,999Weight | 30.9 lbs |
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Frame | Aluminum |
Suspension | Full, 140 / 140mm |
Fork | RockShox Reba |
Shock | RockShox Deluxe Select |
Wheels | 26″ Aluminum |
Drivetrain | 1 × 12 |
Groupset | SX Eagle |
Brakes | Hydraulic Disc |
Seatpost | Dropper |
For This Bike
Based on build material and quality level of the frame, fork, wheelset, groupset, suspension system, and more.
Compare the full Jeffsy model range
View Comparison4'9" – 5'3"
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Mar 2024 · Ben Haworth
The YT Jeffsy Core 4 is a bike that arrives in a box that is not quite perfect out of the box. BUT... there is loads of potential here.
Oct 2023 · Jamie Darlow
YT has reworked its Jeffsy trail bike, adding more tech, more price, and better performance
Pedals better when sat down and stood up cranking
Frame is sleeker and now comes with internal storage
Bikes range from £2,500 up to £5,999 for Core 5
Amazing spec on Core 5, with Fox Factory suspension
Costs a bomb for a direct-sales bike
Frame storage door could be bigger
Oct 2023 · Dario DiGiulio
The new Jeffsy stays true to its trail bike roots, with 145mm of rear travel and 29" wheels.
Jun 2023 · Tom Marvin
A blast from the past that's still a serious contender
Fun, poppy ride quality
Excellent frame details
Good value for money
Some pedal bob when you’re trying hard
Harsh cockpit
Brakes are underwhelming
Apr 2023
The YT Jeffsy Primus 27 steps up an affordable 150mm all-mountain bike for riders 135cm to 165cm tall (or 4’5” – 5’5”); priced at $2,399
Feb 2023
Read our YT Industries Jeffsy Core 2 review and see why this versatile, affordable mountain bike is made for rippers and beginners alike. Read the review now!
Best Bang for the Buck
Solid Spec
Looks the Most Refined
Comfortable All-Day Ride
Shift Performance or lack thereof
G2 Brake Fade
Short Dropper Post
Nov 2022 · Danny Milner
Those who think the youth of today have it too easy look away now, because this Jeffsy Primus is a kids’ bike at least as cool – if not cooler – than anything you could be buying yourself. And if your youngsters look like they could get serious about their riding this will give them an incredible leg-up, opening up burly terrain and big hits for even the youngest of shredder. Be careful what you unleash…this is one of the best kids mountain bikes out there. Need to know Available in 24-inch and 26-inch wheel versions, though not switchable from one to the other Attention to detail extends to narrow grips, custom shock tunes, tubeless prep and more besides Proper tyres open up serious terrain for proper little riders Super active suspension that actually works, even for smaller kids Virtual Four Link design carried straight over from adult sized Jeffsy range No corners cut on the spec, top quality finishing kit from front to back If you started out mountain biking on a rusty Falcon Sierra or wobbly old Raleigh Activator prepare for a shock at how far kids’ bikes have come. And how quickly a quality bike like this awesome looking YT Jeffsy Primo can unleash the proper ripper in your nipper. At a price. Like anything you get what you pay for, and at first glance you know there have been no corners cut shrinking down YT’s popular all-rounder for a younger generation of riders. And the deeper you dig into the spec the more impressive it becomes, the attention to detail underlining a zero-compromise approach that makes the price actually look relatively reasonable – particularly now it’s been reduced by over £400! It starts with the foundations of a sleek looking and well-finished hydroformed aluminium frame based around YT’s Virtual Four Link design, driving a Manitou McLeod shock with 130mm of rear-wheel travel and a four-stage compression switch to configure it to the terrain you’re riding. This is paired with a burly looking, 130mm travel Manitou Machete JUNIT front end whose Expert Air springing promises a kid-optimised response that’s often lacking in the basic forks found on most 24-inch bikes. Quality SunRinglé Düroc wheels are another welcome sight and save a chunk of valuable rotating and unsprung weight compared with the hefty hoops standard on the Marin 24in Rift Zone Jr we had on test at the same time. True, the Minion DHF/DHR tyre combo is probably overkill for all but bike park riding, but points to YT’s intentions, the fact they turned up already tubeless and with Peaty’s valves another satisfying detail. The relatively small 42t top cog on the SRAM 11-speed cassette is another indicator of the Jeffsy Primo’s gravity focused ambitions, even if the stumpy 155mm SRAM SX cranks will help little legs and are acut above the kind of no-name components often found on kids’ bikes. Quality finishing kit from SDG completes the spec, the dinky saddle, 650mm bars and super skinny grips …Continue reading »
Looks fantastic. Kid-optimised attention to detail. Suspension actually works. They’ll love shredding the downhills…
…but the climbs will be a drag on those fat Minions. Not cheap. Limited gearing range. Might not last a growing kid very long.
Aug 2022
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.
Fork | ROCKSHOX REBA, 26“ | 140 mm Travel | 100 x 15 mm Axle | Offset 40 mm | Adjustable Rebound, Air Pressure Travel: 140mm Spring Type: Air |
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Shock | ROCKSHOX DELUXE SELECT, Shock Length: 190 mm | Shock Stroke: 45 mm ≙ 140 mm Travel | Adjustable Rebound, Air Pressure, Custom Tune Travel: 140mm Spring Type: Air |
Headset | ACROS AZX-576, High Cap | 2 Spacer 5 mm |
Stem | E13 BASE 35, Length 40 mm | 35 mm Clamp | Rise 0° | 6061 AL |
Handlebar | E13 BASE 35, Width 760 mm | Rise 20 mm | 9° Back Sweep | 5° Up Sweep | 6061 AL |
Saddle | SDG BEL AIR 3.0, YT Custom | Width 140 mm I Lux-Alloy Rail |
Seatpost | YT POSTMAN V2, Ø 31.6 mm | Length 100 mm | Standard-Remote | Adjustable drop 20 / 10 / 5mm Type: Dropper |
Grips | ODI ELITE MOTION V2.1, Lock On |
Rear Derailleur | SRAM SX EAGLE, 12-speed |
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Crank | SRAM SX EAGLE, Crank Arm Length 165 mm | 30T | DUB |
Shifters | SRAM SX EAGLE, 12-speed |
Cassette | SRAM PG1210 Eagle, 11-50T | 12-speed |
Brakes | SRAM G2 R, Rotor CENTERLINE Ø front 160 mm / rear 160 mm, Adjustable Reach Type: Hydraulic Disc |
Rims | SUNRINGLÉ DUROC, Aluminum Rims 26“ | Inner Width 26 mm | Front Hub 100 x 15 mm, Rear Hub 148 x 12 mm |
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Tires | MAXXIS MINION DHR II, Front: Tire Size 26“ x 2.4 I EXO Casing I 3C MaxxTerra Compound I Tubeless Ready, Rear: Tire Size 26“ x 2.3 I EXO Casing I Dual Compound I Tubeless Ready |
Last updated May 4