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Gravel Tires Tubeless

Donnelly XPlor MSO Tubeless Gravel Tire

The Donnelly X'Plor MSO tire design is a shout out to the Adventure Cycling Association, headquartered in Missoula, Montana. Hence the airport code, MSO, for the tire designation. Developed with the needs and requirements of adventure cycling, the X'Plor MSO Tubeless Tire is a large volume, highly versatile option for adventure, all-road/gravel, commuting, and specific cyclocross riding. The fast rolling design has surprising hook-up in mixed surface riding, and the 700x36mm version will fit just about any cyclocross or gravel-type frame and fork, making it an ideal size. The MSO is also offered in 32mm, 40mm, and 50mm options, but the former is just a little to narrow for true adventure riding and the latter two are limited to disc brake framesets that offer enough clearance to handle the larger size. The development of the tubeless version no doubt had MSO riders cheering, as the the ability to take advantage of high and low pressures without pinch flats, as well limiting puncture flats through sealant use makes the X'Plor a perfect tire for most riders.

The tread pattern is the first reason the MSO jumps out at you. While it looks fast rolling and somewhat solid in the center, a closer look reveals directional vector knob clusters and shapes that do roll fast and pretty smoothly on pavement, but have slight separations and incuts that ensure grip on hard, slick surfaces, such as dusty or wet rocks. Just off the center on both sides are a one-one series of small and larger hexagonal knobs that pitched front to rear. These knobs carry your grip and consistent feel off the center when cornering, offering stability on pavement and grip off-pavement. The top of the shoulder/edge features a combination of the same larger hexagon of the inner line, but is offset with a small triangular knob, that points to the centerline. Again, here is your cornering transition, but with slightly more open space, also a source of traction in softer terrain, especially at lower pressures.

The pure edge tread line is a story in itself. There is a tandem knobset, with a flat edge, five sided, smaller forward tread paired with a larger, mirrored version of the same shape, but which has a beveled top surface that is higher in the rear. Between the mirrored pair, in sequence, are two smaller hexagonal knobs with more space in between. This design is for enhanced grip, stability, and traction, especially in off-road or trail riding situations where softer, or loose material can get sketchy, and despite the fact that this tire says "fast rolling" the hook-up is excellent and confidence inducing. A brilliant tread design all around.

For reference the 700x36 X'Plor MSO Tubeless runs true to it's size. While Donnelly doesn't have rim width recommendations, the narrower the internal rim profile, the narrower the tire will set-up. Of course the inverse is true. Mounted tubeless on a NoTubes 21mm internal width Crest EX rim, at 45 psi, it measured 36.9mm. Donnelly has developed a proprietary tubeless ready construction and it is clear that the walls have been reinforced with rubber, yet there is suppleness that suggests a flexible casing material. The bead is a strong, proven design of heat resistant Aramid fibers so you can run this tire with tubes or tubeless. The surface and tread rubber is a Shore 70A hardness, which offers good wear, lower rolling resistance, and overall durability. Grip is largely a function of the tread pattern and tire footprint, so the tire pressure you choose will be driven by conditions and terrain.

The listed weight for the 36mm tire is 450 grams, with Donnelly's proviso that weights are +/- 8%. This may sound off, but if you have ever weighed tires, you know how much variation there can be. An actual weight on a tested tire was 472 grams, within their parameters, but there have been other actual weights reported right around the listed 450. On the bike, you really don't notice the difference and the durability and strength are appreciated on the course or trail. You want to run an ammonia-free sealant, such as Stan's NoTubes. The tire mounts reasonably and seals exceptionally well. The durability of the sidewall is impressive. The recommended pressure range of the 36mm is 40-60psi (varies in other sizes) though several independent reviews suggest excellent viability down around 30psi, which would be dependent on rider weight, conditions and use. We suggest before setting out on an adventure or trail ride, work through a few pressure tests on a controlled route so you can evaluate what works best for you. We are impressed with the X'Plor MSO Tubeless and we suspect you will be as well. We are also thankful Donnelly took their time to develop this excellent tubeless ready system, which just improved an already great tire design.


  • Tubeless ready adventure, gravel, all-road, commuting, hardpack cyclocross tire
  • Versatile, fast rolling tire with impressive grip, traction and handling capability
  • Tubeless casing is reinforced for wear, fully sealed, features an Aramid bead
  • Rubber is Shore 70A, which has long wear, offers stiffer knobs, grip from tread pattern
  • Can be run tubeless or with tube
  • PSI range varies with size
  • Recommend current sealants like Stan's NoTubes, that are ammonia-free
  • Size: 700x32, 700x36, 700x40, 700x50
  • Colors: Black, Black w/Tan sidewall
  • Size/Weight: 700x36 / 450g (+/- 8%)