Big and Quick: the Clement MSO X’plor 40 Tubeless

Big and Quick: the Clement MSO X’plor 40 Tubeless

The first time I rode a Clement MSO X’plor I was on singletrack hidden within the confines of suburban Boston. I wasn’t sure which impressed me more, the tire or the fact that you could find such exciting riding so close to an urban area. That ride was on a borrowed bike but when I worked with the folks at Seven to design the Airheart, we made sure to give it room for 700C x 40mm tires.

While I really liked the origninal MSO X’plor, I have to admit I did flat on my first big ride on my new Airheart. That was but a minor annoyance. Still, it was a flat, and I suspected that had the tire been tubeless, I’d never have flatted. So I was excited when the MSO X’plor was released in a tubeless version. Just one small problem. It was only 36mm wide.

A 36mm-wide 700C tire works in a great many situations. A great many. But for all the riding I do east of the 101 in Sonoma County, it’s just not enough tire. There have been too many (okay, a half dozen) occasions when I’ve hit a rock hard enough to make the rim bottom out against it.


To the tire’s credit, I’ve yet to flat due to it. Still, I’d prefer not to hit the rim on a rock if for no other reason than I tend to pinch a nerve in my shoulder when I do it, the effect of which has hurt so bad on a couple of occasions it’s caused me to see a flash of light. Which is my roundabout way of saying I’d simply prefer a bigger tire so that I can ride as fast as I want without worrying that I’ll pile-drive a rock.

Which brings us to Clement’s latest iteration of the MSO X’plor: 40mm tubeless. Or in the vernacular, one of the greatest gravel tires in history. Why? Because it’s a big, tubeless tire that grips like a cat on cashmere and rolls like like an 18-wheeler.

For all the talk of 650B I continue to be a devotee to 700C for the simple reason that the bigger the tire, the lower the angle of attack and rolling resistance. I don’t want to do anything to reduce the circumference of the tires I roll on. The larger diameter tires allow me to run rubber with more tread while reducing the rolling resistance penalty. However, that’s not even my biggest reason to love a 700C x 40mm tire. Attack angle. With all the rock that I encounter on my rides, I want the bike to roll over that stuff as readily as possible. I’ve learned that the more I get bucked around by rocks the less power I deliver to the pedals, so the slower I go. If I have to stop pedaling because my butt is in the air, that represents a serious loss of power.

While the blocks on the tire are relatively small and closely spaced, the grip in corners is consistent as a drill sergeant and when they do break away, they do so with the reluctance of my son putting his shoes on. Lifespan on a tire like this is always a question and I’m pleased to report the 70-durometer compound will outlast the some of our current politicians.

I’ve had friends observe that a 650B x 50mm tire isn’t that much smaller than a 700C x 40mm tire when inflated to 40 psi (we’ll leave the ideal inflation for each tire for a different conversation). My response is that 26-inch tires aren’t that much smaller than 27.5-inch tires and they aren’t that much smaller than 29-inch tires, but when mountain biking I crash more on 27.5 than I do on 29 and I crash way more with 26 than I do 27.5. I’ve also noticed I’m much more able to control slides on bigger tires/wheels.

The tubeless MSO ($72 suggested retail) runs a little heavier than either the 60 or 120 tpi versions of the tire. While the 120 tpi tire in the 40mm width is said to weigh 384 grams, the tubeless version weighed 566g. I’m okay with the increase as it drops rolling resistance, increases grip and reduces the chances of a flat. That going to a larger, heavier tire could offer so many compelling reasons to recommend it isn’t something I’d have thought possible 10 years ago. How times change.

One detail we need to clarify: these tires will become known as Donnelly Sports; the licensing agreement with Clement is ending, but all of the tires in the line will remain unchanged. Just the look on the hot patch will change.

Final thought: If these had been available in 1987, I might never have taken up mountain biking.


If you value independent media, please lend your support to RKP.

Subscriber Options

To learn more about our new subscription program, please read this.

, , , ,


    1. Author

      The 36 is an amazing tire and if you don’t have rock the way we do, it’s plenty. It’s great until it’s not great, hence the need for the 40.

  1. Sean

    I’m on-board with the bigger wheels and lower rolling resistance but the advantage of a larger tire volume is huge on rough roads. I observed this at Grinduro with my friend rolling away from me on the first downhill on his 20 year old 26″Hunter MTB with drop bars. I was on a Cannondale Slate with 650b x 42s plus the fork and couldn’t stay with him.

  2. Kurt

    Update, 700×50 MSO for the monster crossers. It’s RAD!!! Fits on the front of my Giant TCX, but 45 is Max on the rear.

Leave a Reply

Your email address will not be published. Required fields are marked *