When I decided to ignore conventional (26″ wheeled) international touring wisdom, and buy a 29+ Surly ECR, one of my first questions was to find out what was the narrowest tire width that could be run on Surly Rabbit Hole (50mm wide) rims. It wasn’t a selling point when Ed at Mighty Riders recommended 2.35″ as the limit. It’s not that I really think anyone should be riding tires narrower than 2.35″ if their bike has as much tire clearance as the ECR. But, down in Chile, for example, it’s easy to find a 29×2.0″ tire in any larger town, and all but impossible to find one of the few 2.4″ models available in North America.
Internet searching yielded early rumours of the Velocity Dually 29, at 45mm wide, as a perfect alternative. Just a tad narrower than the Rabbit Holes, the numbers added up for it to run a 2.0″ tire. The catch was that this was September, 2013, when I was figuring this all out. The release date for the Duallies was Sept 9th. Then Sept 20something. Then late October. So the Duallies were basically completely untested. Trusting Velocity to not completely screw the pooch on these rims, I ordered some anyway. I finally got mine in late November, well before most people.
I built the wheels myself, using Sapim straight gauge spokes and Sapim brass nipples, for touring robustness. Tangentially, I think butted spokes can also make excellent, strong touring wheels. The rear is laced onto a Rohloff Speedhub, and the front onto a Velocity ATB Lightweight Disc, which as far as I know is simply a rebranded Novatec hub. I’m in the habit of looking to Taiwainese manufacturers for affordable excellence, and Novatec is one such excellent Taiwanese brand.
The Duallies are marketed as a tubeless ready rim. But, their rim profile lacks the sophistication of UST rims, which have bead shelf ridges that hold the bead laterally to prevent loss of seal from a hard side-impact.
The Surly Rabbit Hole and the generic UST rim profiles, shown above, both appear to have bead shelf ridges. The bead shelf on the Dually gently slopes inward toward the centre of the rim, with nothing physically in the way to prevent a hard impact from forcing the tire off the bead shelf, which could unexpectedly sent the rider into the dirt.
It’s important to note that while the Rabbit Holes appear to have a superior rim profile, they cannot even be broadly considered tubeless-ready. On tubeless tire set-ups, the seal between the tire and the rim is not at the side of the bead/bead hook, but rather between the bead shelf and the inside (bottom?) edge of the tire bead. The diameter of the Rabbit Holes is not large enough for a tight seal to form between the shelf and the inner bead surface. Many people have had great success using a split inner tube to build up this surface on the Rabbit Holes, resulting in a very safe and effective “ghetto tubeless” set-up. But, no one calls rims that need a split tube tubeless-ready.
Velocity justifies calling the Duallies “tubeless-ready” because the diameter of the bead shelf is large enough to create a tight seal when matched with tubeless-ready tires. I’ve been using Surly Knard 29 x 3″ tires which, of course, are not made to the same standards as tubeless-ready or UST tires. So, between the lack of bead shelf ridges and my use of Surly tires, I ended up having to build up my rim with multiple layers of tape.
First I attempted to build a bead shelf ridge, using 5mm wide strips of Gorilla Tape. Then I added a full (45mm wide) layer of Gorilla Tape to seal everything. I initially set it up with just these two layers, but the amount of sealant seeping out at the bead made it clear that the seal was not going to last when I started riding hard. After adding a second full layer of tape (45mm wide), I was still able to set the bead – with some effort – using a floor pump. When no sealant seeped out at the bead, I knew I had seal that might last. And last it did.
Lacking experience, I added only 3 oz of Stan’s sealant to each tire – maybe half as much as I should have for my 3″ wide tires. Since liquid sealant automatically seal any punctures, it became clear that the sealant had all but dried up, only four weeks later, when a puncture failed to seal a week into our ride down the Carretera Austral. I added 1 oz to that tire, and re-inflated it without trouble. Amazingly, despite the dried up sealant, my front tire held air for another six weeks – through hard, rocky descents and thorn-ridden trail while running low pressures on a loaded bike. Even then, an additional 1 oz of sealant would keep it going for another month, until I could finally buy some more sealant.
I ended up having to use a tube in my rear tire for about a month in Patagonia. These weeks made it all too clear that tubeless and fat-tired touring belong together. Besides the endless slow-leaking punctures, I could actually notice more rolling resistance in my rear tire. Further, I had to be careful of pinch-flats, and could not run the rim-destroying low pressures I’d come to prefer. When I finally found a source of (Joe’s) sealant, I set up my rear tire with 6 oz of the fluid – a much more appropriate volume for touring robustness outside North America.
Between the touring loads – albeit light – and the low pressures that make 29+ such a joy for touring, I’ll admit that I have bottomed-out my tires, feeling that “clang” of a rock directly on the rim, a little too often. The damage? A sidewall dent and a handful of scratches.
The rims are straight and round, after over 5000km of dirt and about 15 aggressive trail days, but that has always had more to do with the construction of the wheel than the rim alone. The alloy from which the Duallies are made seems softer than that of the Rabbit Holes, which might mean they scratch and dent a bit easier. My dent hasn’t affected its ability to form a tubeless seal, so I’ve done nothing about it.
If the objective is to get the widest-possible footprint out of the 3″ Knard tires, the 50mm wide Rabbit Holes will perform better. Before getting my Duallies, I borrowed Surly Rabbit Holes, and built them into wheels. Their additional lateral stiffness was noticeable in the truing stand, compared to the Dually. Since I never rode the Rabbit Holes with a touring load, I’m reluctant to say that I noticed this lateral stiffness on the trail. But I might have.
Importantly, the Duallies are stiff enough that my bike feels rock solid bombing down rocky roads (at up to 69km/h) with a light, bikepacking-inspired, touring load. Further, with the tape bead ridges, and double layers of tape, I haven’t burped the tire once, and I feel safe enough to have gone that fast down some roads surfaced with lose eggs and baseballs.
The weight savings of the Dually over the Rabbit Hole are not so huge that I wouldn’t recommend Rabbit Holes to anyone who thinks they’ll run Knards exclusively. Since Rabbit Holes have been made tubeless with the split-tube method so successfully, the advantage in terms of tubeless is really a question of weight. All else equal, the Dually will build into a lighter tubeless set-up.
The cost of the weight-saving doesn’t appear to come at a significant cost to durability or strength. At least until Stan’s releases their protype 52mm wide rim in 29″, the Dually will remain my preferred tubeless 29+ rim. Hopefully Stan’s can undercut the (brutal) $135/rim price tag of the Dually and Rabbit Hole.
Overall, mid-fat and fat bikes are changing the face of cycle touring. Even though tubeless set-ups and fat tires fly in the face of everything that is considered traditional touring wisdom today, I will not be surprised if ten years from now they are the norm for dirt-road touring. If not, I can promise you that I’ll still be a die-hard fan. I’ll just carry 8 0z of extra sealant an one spare tube, rather than 3 oz and two spare tubes like on this last trip to Patagonia.
I impatiently await more 3″+ tire options. Hopefully someone will release a durable 29er tire with an 80mm casing and an 80mm tread (3.2″), which would undoubtedly fit in my Rohloff-equipped Surly ECR.
We’ve recently made an Off Route Facebook page, where we’ll be posting more frequent updates of where we are and what we’re up to, as well as lots of extra photos. You can “like” our page if you’d like to follow the adventure more closely.