YT Jeffsy Primus Junior 26-inch FS Ripper In For Test

Whether for riders with shorter inseams or kids coming up in the sport, the Jeffsy Primus Junior 26" platform from YT Industries looks like a sweet step into mountain biking.

Whether for riders with shorter inseams or kids coming up in the sport, the Jeffsy Primus Junior 26″ platform from YT Industries looks like a sweet step into mountain biking. YT recommends the single-size bike for riders who are between 145 and 160cm (57-63″) from the ground, and there’s a 24″ wheeled version for riders in the 135-150cm (53-59″) height range. The 26er has 140mm of squish front and rear, and bikes with 24″ wheels get 130mm of balanced travel. My daughter, who will be testing this sweet 26″ ride, is 159cm tall, and she’s looking forward to riding a bike that’s on the smaller side of the bikes she’s tried.

It’s been a hot minute since we’ve seen that nine fliped upside down.

The Primus Junior has a flip chip to adjust the geometry between a 65.5° and 66° head tube angle and to lean the seat tube between 76.5° and 77°. My daughter only cares about coasting downhill, so we’ll be leaving it in the slack setting. The bike’s height parameters are stretched around a short 397mm reach, an average 355mm seat tube length, and a very short 95mm head tube. On the first ride, my kiddo mentioned that the handlebar feels super low, and there is only a single 5mm spacer above the stem to adjust that height. Chainstays on this single-size bike are 415mm long, cutting the back end measurement as close to the front end length as possible for a comfortable trail balance.

These smaller aluminum frames use the same Horst link suspension design as the longer-tubed Jeffsy models, and the similar shock placement means there’s no space for a water bottle in the front triangle. All the cables and housing are run internally, with clean entry-ports on the head tube that should prevent the common rubbing and paint scratching issues around that area. To finish it off, the Jeffsy 26″ has the same chain stay and down tube protection as the larger models, and adding an aftermarket paint-protection layer to the bike might keep the flat-black paint fresh for a little while longer.

5mm of stem height adjustment above and below the stem.

Like the 29er Jeffsy I tested a while back, it would be great if YT could cut the steerer tube on this bike with a little extra adjustment space that riders could chop off later if they prefer lower bars. The only way to adjust bar height now is to mount a longer stem with a rise-angle or swap the bar for one with more rise. While bar height won’t be an issue for everyone, this could create unnecessary component expenses for folks who like steeper and more aggressive trails and riders who are at the taller end of the Jeffsy 26″ spectrum.

The Jeffsy Primus Junior 26″ comes with a build kit that’s similar to the brand’s Jeffsy Base 29″ model, including a set of Maxxis Minion DHR II tread at both ends wrapping a set of Sun Ringlé Duroc hoops. The 140mm Manitou Machete Junit fork and RockShox Deluxe Select+ shock take care of impacts with all of the adjustments most junior riders could want. The SRAM SX Eagle drivetrain brings the weight up a little, leaving the bike with a roughly 31lb total heft that’s all slowed by a set of SRAM Guide R brakes. The rest of the build is largely comprised of house-brand components, including a 100mm Postman dropper. This build retails for €/$2,299.

Click over to the YT page for more info on the Primus Junior 26″, and stay tuned for the full review in 2022.