Donnelly MSO 650B x 50mm Tires: Getting Rolling

 Donnelly MSO 650B x 50mm Tires: Getting Rolling – by Grannygear

Many gravel bikes in this day and age are coming from the factory set up to run both 700c and 650b wheel sizes. Typically the smaller wheel allows for at least a 47mm tire to fit in there and more commonly, like the new V4 Warbird that Salsa just rolled out, they will handle up to a 2.0/2.1 27.5/650B tire.

That dual wheel option adds quite a bit of versatility to the bike. One of the reasons I swapped my older Warbird for the Lynskey GR 250 was the ability to run that smaller wheel-bigger tire combo. But I have not done that very often. After riding these new tires, the Donnelly X’Plor MSO, I am thinking I have been missing out.

The Donnelly MSO 650B X 50mm tire.

Set the WAYBAC machine to a year or so ago. I was riding a set of WTB Nanos in the 650bX2.1” size on the new-to-me Lynsey GR250 when I pointed the bike at a particularly nasty rise in the dirt road I was on. Deeply rutted from 4×4 traffic after some heavy rains, what parts of the road that were not dried, clay waves of hardened dirt, were pools of muddy water and exposed baby head rocks.

Up I went with very little drama. Well, that was fun! The extra drag of the bigger tire on the paved climb that got me here was soon forgotten as the rest of the ride was a revelation of, to quote Tigger, “bouncy, trouncy, fun”. The bigger casing of the 2.1 and the more aggressive tread allowed me to ride the bike more like a mountain bike of old with no suspension and narrow, oddly shaped bars!

Grannygear demonstrates how the folding bead 650B X 50mm MSO is a bit stiffer than some other tires.

But the Nanos were not tubeless ready in that size (what is up with that WTB?) and I never ran them again. So yes, I have dabbled with the 47mm size in 650B, but I had not revisited the 50mm (2.0/2.1) size till now. Recently I was chatting with Guitar Ted and mentioned I was thinking of revisiting a smaller diameter but poofier 50mm tire but was not sure what was out there. He mentioned the Donnelly X’plor MSO in that size and after an email or two, I had a set in the bag.

What It Is: When I got them out of that bag, I picked up one of the tires to unwrap it and thought, “Heavy critter!”. I unfolded it and noted the casing, with what felt like a good bit of rubber in it, allowed it to stand upright without collapsing, something most tires will not do. On the kitchen scale of truth and justice, I weighed them at 661g and 662g. Ouch! I had to look up the 700×42 Resolutes in my notes and realized I was adding about 200g each tire in rolling weight. The 650B wheels I would be using were about the same weight as the 700c ones, so no savings there to offset things.

Hmmmm…how to put this in perspective? Well, a bit of googling showed that the WTB Race Nanos in this size were the same weight as the X’Plor, so that was interesting. As well, when you read the ad copy for the X’Plor MSO tire, you see this:

The X’Plor MSO is an tubeless-ready adventure tire designed for the most ambitious adventures. The combination of smooth-rolling center knobs and aggressive shoulder lugs provide great traction and durability for gravel roads, trails, urban assault and even pavement.
The MSO tire is named for the airport code of Missoula, Montana, home of the Adventure Cycling Association. Donnelly’s X’Plor adventure tire series is designed to bridge the gap between pavement and blazing your own trail. Each tire within this series is designed for multiple conditions from off-road touring, to gravel racing, to just getting outta’ Dodge.

So if we keep this in mind, the burly feeling casing of the X’Plor makes sense. Light weight tires come at a cost and that cost if often played out in trail side tire repairs and costly replacements. The tread pattern is interesting with not much in the way of blocks or gaps, but rather a close pattern of mini teardrop shaped knobs set into a semi-chevron pattern and with a decent center ridge effect. It looks like a fast, smooth rolling tire.

With a slosh of Orange Seal Endurance formula, the X’Plor MSO tires set up with a floor pump on the WTB KOM 21 rims. Nice. They have not weeped one tiny bit since then, showing another good thing about a casing with more rubber in it.

I have had many rides now over varied but typical So Cal conditions. Much more on that later, but I have found that the X’Plor MSO tires have been a real blast to use and I look forward to many more rides on them. Next post we will start to unpack that as I head to the rugged jeep roads of some high mountains near me, a perfect proving ground for a “tubeless ready adventure tire”.

Grannygear with the Donnelly 650B X 50mm tires on his Lynskey GR 250

I will also be thinking out loud about the pros and cons of this wheel and tire size as compared to my normal 700X42mm set-up, as I have been flip-flopping back and forth a bit depending on the ride I am doing. Would I convert full time to 650BX50?

More on that as we go.

Editors Note: Yes, there is a 700c X 50 MSO as well which RidingGravel reviewed here.

Note: Donnelly sent over the 650B X 50mm MSO model tires for test and review at no charge to We were not bribed nor paid for this review and we will always strive to give our honest thoughts and opinions throughout.

ResoluteAbout The Author: Grannygear hails from SoCal and spent most of his cycling days as a mountain biker from the formative years of mountain biking all the way up to the present day. His day job is in the tech sector, but he has spent time writing about off road 4X4’s, 29″ mountain bikes, and cycling in general. Grannygear and Guitar Ted have worked off and on together since 2009 after a chance meeting at Interbike. With gravel cycling on the rise, Grannygear has been exploring how this genre’ works in SoCal and now does guest pieces for in his spare time.



Author: Guitar Ted

Guitar Ted hails from Iowa. Home of over 70,000 miles of gravel and back roads. An inaugural member of the Gravel Cycling Hall of Fame and Co-creator of Trans Iowa in late 2004- Guitar Ted has been at the forefront of the growth of gravel events and riding since then. Creator of Gravel Grinder News in 2008, he produced the premier calendar of gravel and back road events. GT joined forces with Riding Gravel in late 2014.

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14 thoughts on “Donnelly MSO 650B x 50mm Tires: Getting Rolling

  1. I’m curious to hear if much has changed as far as how these tires hold up over the long haul. I’ve gone through a few sets of the 700×40 version of these, and my biggest complaint has always been that the rubber is so soft that the center tread wears away to practically nothing while the rest of the tire is still looking almost new. I have been running the non tubeless versions, so losing all the tread on the center line results in lots of flats.
    My riding is definitely a mix of paved and unpaved, and I found that the soft rubber made for a sluggish feel on the road, and road riding is probably the cause of the premature wear on the center line.
    So, I’d love to hear more about your experiences with tread wear over time on these newer versions. Thanks for all the info!

  2. With Gravel tires getting ever wider, I’ve been thinking that gravel bikes should come with ~i28mm (i=inner width) rims but also have enough frame cleareance for 2.6in wide tires. Doing this would make it possible to use 650×47 tires up to 27.5×2.6 tires. That would allow for the use of mountain bike tires. Many of the XC race tires are very light and very lightly treaded. For example, there are two 27.5×2.6 Kenda Saber Pro tires with a claimed weight of 550gm and 635gm. Not much difference in weight to the MSO’s. With 2.6 tires, the tire pressure could be set very low and make for a very comfortable ride. Maybe gravel bikes haven’t gotten wide enough?

    1. @Plusbike Nerd- Or maybe we are really talking about drop bar mountain bikes like the Fargo? There is a point at which a line gets crossed, and the current trend to have swappable wheel sizes in a gravel/all road bike is blurring those lines. Furthermore, dropper post spec and short travel front suspension further blurs those lines.

      I think where we get to that line is when a road bike spec drive train no longer works due to tire/frame/crank clearances. You may point to 1X, but until rear cassette ratios are tightened up and you can add about five more cogs back on the rear wheel to do it, gear range will never approach what a double crank can do with a closer ratio cassette. I’m not saying you couldn’t get there with a 1X set up, but I am saying it would have a very limited appeal for road goers. That includes gravel roads.

      It’s an interesting thought you have, but it sounds like a mountain bike, no matter how you slice it.

      We have a bike arriving for test and review which I think might help us dissect this conundrum further. Stay tuned……

      1. @Guitar Ted
        When I look at the picture above of your Lynskey, I don’t see a mountain bike or a road bike. I see a bike with its own unique attributes and I am wondering what is the the ideal tire and rim, size and width that will make a Gravelbike the best machine it could be. I am trying to take a scientific approach and keeping an open mind about what works best. 15 years ago when we were all riding 26er mountain bikes with narrow tires, narrow rims and short travel, I didn’t imagine that I would be riding a long travel mountain bike with 29×2.8 tires on i35 rims in the present. Maybe, a 650×47 tire on an i23 rim makes the ideal Gravel wheel. But maybe, a Gravel specific 26×2.6 tire on an i28 rim is even better. Higher-volume, low-pressure tires have done amazing things for mountain bikes. Could they also improve Gravel bikes? I don’t know, but I sure hope that we don’t get close-minded before we try it out.

        I recently took a test ride on the 2019 Salsa Fargo with 29×2.6 XC-race tires on i29 rims. I found it to be suprisingly fast on pavement while being very comfortable and capable on gravel. It’s down side is that it is a heavy steel bike with lower-end components. I can easily imagine an “enlightened” 20 pound version of this bike making an excellent Gravel bike. However, while mountain bikes benefit by having taller 29 wheels, I think Gravel bikes benefit from shorter 27.5 or even 26 wheels as a way to minimize weight and keep the wheel height similar to a road wheel.

        When I look at your Lynskey, I see a bike that is part road bike and part mountain bike but which is also neither. Let’s allow the Gravel bike to evolve into the best bike possible for its intended purpose and not get stuck in either the road bike or mountain bike paradigm. Now, if some company would make Gravel bike with 26×2.6 Gravel specific tires, we could test it out!!

        1. @Plusbike Nerd- Two things- First, that is not my bike, but Grannygear’s who was the author of the piece here.

          Secondly, you said “..scientific approach”? Okay, how about looking at physics, geometry, and mathematics? In that case, the issue becomes the physical impossibility of objects occupying the same space- IE, Tires that are as big as you are saying, having road bike capable gain ratios, and how frame geometry works with both of those things. I’m not at all being “stuck in a road bike or mountain bike mentality”. I am saying that the industry has standards set which are accounting for lengths, widths, and performance intentions for the humans that integrate with the bicycles that they ride. In light of this “science”, my previous points are valid. It isn’t “either/or” because of my opinions, it is simply the reality of things.

          Could that reality be changed? Certainly. However; it would only be possible by dramatically affecting how we integrate with bicycles, and in many cases, that would be negative in nature. See fat bikes as a great example, which for many people, are an untenable option due to the physical/mathematical/geometrical constraints of having 4″+ tires and chain driven drive trains.

          I’m not talking about anything which isn’t well understood by bicycle designers. It is why, on the Fargo which you tried, the drive train is “mountain specific” and does not have the ability to have a “road type” drive train. You simply cannot put bigger chainrings on without adversely affecting other elements of the system and how humans integrate with that system.

          So, in the end, it isn’t my opinion, or anyone else’s that is “not allowing” what you are proposing here to become reality.

        2. @Plusbike Nerd…the reason you do not see one or the other is because neither of those is there to see. We certainly are in the formative years of this genre and what works and does not work. I can see rims being wider to allow for more support to the tire and more volume out of the casing, but then I would be gaining weight in the rim. On MTBs, that wide rim allows for lower PSI which pays big time off road on rough trails. But I don’t want that low PSI on the road. So while a bit wider rim might be OK, I think there is a place to where it does not make sense for the way I ride. I disagree on a smaller wheel approach unless you scale up the tire a bunch. Without suspension, that bigger wheel is a biiig bennie. I do really like the 50mm size tire in 27.5 for heavier off road use, but it can’t beat a 700cx42c as an all-rounder. You only minimize weight when shrinking the wheel if you keep the tire small. Poof that tire beyond 2.0 and you gain all that weight back at the outer edge of the wheel, along with adding all kinds of crap handling on the road. I use nothing but Plus on my MTB (27.5×2.8) and for the non-aggressive way I XC trail ride, it is great. But I don’t want the same attributes on my gravel bike for the way I use it and I bet the vast majority of users feel the same way. gg

          1. @Guitar Ted and grannygear

            Sorry I got your names mixed up. Thanks for resonding to my comments. I’ve been riding a Crossbike for 20 years but the widest tire it will take is 700×35. While it makes a great road bike, once it gets on Gravel it sucks. It’s a bone shaker that plows through Gravel. I’m interested in buying a new Gravelbike but I want to be sure that it is comfortable on Gravel and handles confidently—therefore my concern about tire width. Maybe 650×50 is wide enough?

          2. @Plusbike Nerd

            Depends on what kind of gravel do you ride. Gravel roads can be pretty damn smooth but personally I take my gravel bike everywhere. It has 622-43mm tyres, it can handle any kind of gravel pretty smoothly, I find the limits when I try to ride a slightly rougher dirt road at any kind of decent speed. All those humps and bumps and holes in the road that a tyre simply can’t absorb go straight to my neck. I can’t maintain speed and I get so beat up.
            I’ve tried some 27.5×2.25s in the front just as a test. While it helped immensley on rocky, rooty terrain, it still couldn’t absorb all the bumps on a dirt road like even a 100mm suspension fork could.

            I’d rather have a suspension fork instead of 2.6 tyres.

            While you can certainly make a plus tyre light, those things are like balloons. Although the industry doesn’t always follow what would be actually best for the end user, if you look around most companies in the MTB world started to move to 29 again with tough, more aggressive 2.5-2.6 tyres instead of fragile 27.5×2.8-3.0 tyres.

    2. Guitar Ted is right. Look at what a mountain bike frame does to achieve that kind of clearance with chainstays that are not super long.
      73mm BB, usually a boost rear end, so that also means a boost specific chainline with a boost offset chainring, and the max 1x chainring size is usually 32-34T. Most of the time no FD either.

      At this point I agree that you’re talking about drop bar MTBs.

    3. @Plusbike Nerd

      What about rim weight? Yes, those Kendas are light, but I suspect you’re not going to run them with 20-23mm ID rims. 30mm ID rims weigh a ton.

  3. I love how the MSO rides on gravel and they are damn near bulletproof. When I’m in a race it’s what I count on to get me to the end! I am thinking about the 650b for my Pro GR and it’s nice to know they’re available this size.

  4. Was thinking about this on a ride the other day and @Boni brought it to mind: When you have a smallish tire, like a 35mm or 38mm even, the tire is the limiting factor for how fast you can ride more demanding surfaces. At some point, you simply overwhelm the tire. But when you get to a 2.0 650B tire, well the bike becomes the limiting factor, or at least the rider’s ability to hang on, steer, and keep it pointed in the intended direction.

    Even though the time is big enough for pretty high speeds on tricky roads, you still have a rigid bike and drop bars to deal with, not to mention the somewhat aggressive geometry for something that is bombing a fireroad.


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