A 27.5″ aluminum frame mountain youth bike with upper mid-range components and hydraulic disc brakes. Compare the full range
|Travel||150mm rear, 150mm front|
|Drivetrain||1 × 12|
For This Bike
1 × 12 — 12 speed
Jeffsy Primus 27
Based on build material and quality level of the frame, fork, wheelset, groupset, suspension system, and more. Learn more →
5'0" – 5'5"
Tom MarvinJun 2023
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
Brakes are underwhelming
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
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!
Danny MilnerNov 2022
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.
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.
Richard OwenAug 2022
Like Robocop or the Six Million Dollar Man, YT have rebuilt the Jeffsy with top notch tech to be (even) better than it was before
Matt BeerApr 2022
Following the recent release of YT's Capra and Decoy MX Uncaged 9 builds is the trail-friendly 150mm Jeffsy Uncaged 8.
Lydia TannerDec 2021
A great value with an appetite for rowdier trails. .
Pedal bob had us using the lockout on long climbs
Slightly limited water bottle space
Could use stronger brakes
ROCKSHOX LYRIK BASE, 27.5“ | 150 mm Travel | RC | 100 x 15 mm Axle | Offset 44 mm | Adjustable Rebound, Air Pressure
ROCKSHOX DELUXE SELECT, Shock Length: 230 mm | Shock Stroke: 60 mm ≙ 150 mm Travel | Adjustable Rebound, Air Pressure, Custom Tune 0L1230x60mm | R |Custom Tune 0L1| Volume Reducer
ACROS AZX-576, High Cap | 2 Spacer 5 mm
E13 BASE 35, Length 40 mm | 35 mm Clamp | Rise 0° | 6061 AL
E13 BASE 35, Width 760 mm | Rise 20 mm | 9° Back Sweep | 5° Up Sweep | 6061 AL
SDG BEL AIR 3.0, YT Custom | Width 140 mm I Lux-Alloy Rail
YT POSTMAN, Ø 31.6 mm | Length 125 mm | Standard-Remote
ODI ELITE MOTION V2.1, Lock On
SRAM SX EAGLE, 12-speed
SRAM SX EAGLE, Crank Arm Length 165 mm | 32T | DUB
SRAM SX EAGLE, 12-speed
SRAM PG1210 Eagle, 11-50T | 12-speed
SRAM G2 R, Rotor CENTERLINE Ø front 200 mm / rear 200 mm Adjustable Reach
SUNRINGLÉ DUROC 35, Aluminum Rims 27.5“ | Inner Width 31 mm | Front Hub 100 x 15 mm | Rear Hub 148 x 12 mm
FRONT: MAXXIS MINION DHF I REAR: MAXXIS MINION DHR II, Front: Tire Size 27.5“ x 2.4 I EXO Casing I 3C MaxxTerra Compound I Tubeless Ready I Rear: Tire Size 27.5“ x 2.3 I EXO Casing I Dual Compound I Tubeless Ready