The Donnelly GJT Tire, a Predictable All-Rounder [Review]

Donnelly GJT tire

It’s rare to find a mountain bike tire that corners predictably right out of the box, but that’s exactly what I experienced with the new Donnelly GJT. I’ve been testing the 29×2.5″ GJT at the front end of a short-travel trail bike this spring and have been impressed with how well the tire performs.

Donnelly GJT tire specs

The Donnelly GJT tire features a 120tpi construction with sidewall protection. The high thread-per-inch count promises a more supple ride feel, while the sidewall protection is designed to reduce the chance of pinch flats and tears.

Donnelly markets the GJT as a 2.5-inch tire, and I found they measure almost spot on with 32mm rims at 63mm (2.48in) wide. On a narrower, 30.5mm rim the tires only spread to 60mm (2.36in). Rims in the 30mm range are not uncommon so riders should be aware they may not get the full width they’re hoping for with rims narrower than 32mm. Nevertheless, the tire doesn’t look much narrower than 2.5in on a 30.5mm rim, and if I hadn’t measured I probably wouldn’t have noticed.

Subjectively I would say the GJT tire compound feels sticky-ish; that is, not very firm but also not so soft that it’s going to leave a mark on the gym floor. According to my durometer the rubber measures 58a which should offer a good balance between grip and longevity. This 29×2.5″ tire sample, with tan walls, weighs 960g.

Inside the tire.

Naturally the tires are tubeless-ready, and I had no issues installing and airing them up at home. The inside of the tire features an unusual orange-peel texture, though it’s not clear how of if this affects performance.

Donnelly GJT tire

Donnelly Tire – In the dirt

GJT is the airport code for Grand Junction, Colorado, and Donnelly says this tire design was inspired by the trails there and also in Fruita nearby. If you’ve never been, the trails around Grand Junction tend to offer riders two flavors to choose from: fast and flowy, or rocky and gnarly. On fast and flowy hardpack trails with just a bit of crust on top, the GJT handles like a dream, with the transition knobs predictably leading into the stiff side knobs as the tire goes horizontal in the corners. The GJT handles rocks and roots with similar confidence, grabbing onto and pinging off obstacles like a much burlier tire.

I landed more than a few jumps with my front tire awkwardly hitting the ground at an angle, and never once washed out, thanks in part to the sturdy side knobs which quickly bring the tire back on track. In spite of running just 15psi, and given the 120tpi construction, the GJT tires never felt too floppy, nor did I experience any burps or pinches.

The other thing about Grand Junction is that all of the trails tend to stay dry and dusty for most of the year, and based on my experience I wouldn’t necessarily pigeonhole the GJT as a dry conditions tire. The wide-open tread design sheds mud well and has no problem navigating the damp and at times greasy trails here in the South. (Donnelly has another mountain bike tire called AVL, which was inspired by the riding around Asheville, North Carolina, which I’ll be reviewing next.)

On true hardpack the GJT rides like a fast roller, though that’s certainly not the focus with this tire. I think it would be fine as a rear tire, though the tread doesn’t feature dedicated braking bars like the AVL or the Maxxis Minion DHR II.

Bottom line

Donnelly may not be a household name when it comes to MTB tires, but that’s likely to change as folks try the GJT for themselves. Offering a responsive ride feel, excellent transitions into the corners, and a grippy compound, most trail riders will find the Donnelly GJT makes for an excellent all ’rounder.

Party laps

  • Predictable transitions and tall, stiff side knobs
  • Supple ride feel
  • Good mud shedding and grip

Pros and cons of the Donnelly GJT mountain bike tire

Dirt naps

  • Only 29×2.5″ size currently available
  • 120tpi construction not ideal for more aggressive riding
  • Need a >=32mm-wide rim to achieve advertised tire width