One of two wheels is built for my Surly ECR, composed of a SRAM X7 hub and a Surly Rabbit Hole rim. The 50mm wide Rabbit Hole rim is one of several options in the 29+ genre, alongside several conventional doublewall rims in excess of 30mm. Choices include two Velocity rims, the Blunt 35 (35mm) and the Dually (45mm), both of which claim to be ‘tubeless ready’, but some have called Velocity’s tubeless claims into question. The 47mm Northpaw rim is a true singlewall rim (with cutouts), and is available from Schlick Cycles. A 52mm Stan’s rim is rumoured to be coming this season, bringing Stan’s surefire tubeless features to bike with big tires. Currently, the Rabbit Hole is the widest 29+ rim available, engineered like other Surly fatbike rims as a combined singlewall and doublewall extrusion with cutouts in the center singlewall section. For winter riding, wider is better.
Considering that my ECR is doing work alongside real fatbikes here in Anchorage, it is important to give myself the widest footprint possible, to ensure the best flotation and traction in tough and changing conditions. For this winter, at least, there will be two bikes in the stable– the Salsa Mukluk 3 and the Surly ECR. Come spring and summer, the bikes will dual for my attention as we set off traveling. Until then, the bikes will remain as two distinct concepts, with unique specialties.
From past experiences, a tubeless system promises less rolling weight and a more supple tire system, in addition to eliminating flats. I hoped to install the Knard tire onto the Rabbit Hole rim, tubeless, with no more than a few layers of duct tape to seal the rim and build up the rim bed. The tire fit nicely on the rim with only the Surly tape installed (it was not loose, like some older Surly fatbike tires), and when inflated with a tube, I sensed a strong bead lock. It would be easy, I figured.
The SRAM X7 hub is my new favorite inexpensive quality hub. For $50 or less (I grabbed this one for $33 online at Tree Fork Bikes), the hub features sealed cartridge bearings, a nice machined finish, and a quality three-pawl freehub system which is visibly packed with grease when new. Lael and I used these hubs all summer and they never missed a beat. The bearings in both hubs feel almost new. The closest competitors are Shimano’s Deore and XT loose ball bearing hubs. While the manufacturing quality is good, the design of these Shimano disc hubs has proven to loosen prematurely, resulting in an unnecessary amount of hub maintenance and a premature death. With a sealed cartridge bearing, no matter how much the bearing surfaces are ruined by neglect and harsh conditions, the hub body is never compromised. I really do wish Surly would stop speccing all of their bikes with Deore disc hubs; SRAM X7 hubs please!
Surly Rabbit Hole rim and SRAM X7 hub, laced with straight gauge spokes on the drive side and butted spokes on the disc side, due to a limited availability of butted spokes.
Install a layer of hi-visibility reflective ribbon inside the rim cutouts, backed with a layer of clear packing tape. The flexible nature of duct tape may work better as a backing to conform to the rim and create an airtight seal in the first layer of tape. With a blast of air from a small compressor, the tire does not seat, but it seems close.
The valve has begged for attention for some time. I forced the knurled nut off the stem and cleared a blockage of Stan’s latex sealant. It is best to remove the core from the valve when seating a tubeless tire that requires a lot of air (but not the brass stem). The larger passageway allows more air to enter the tire at once.
With two layers of duct tape, in addition to the reflective ribbon and one layer of clear packing tape, the tire easily pops into place, Without sealant in the system, the tire loses air in less than a minute, not entirely uncommon when seating tubeless tires. However, some tires hold air overnight without liquid sealant.
Hoping that sealant will coagulate in the zones of air leakage, I inject 2 oz. of Stan’s into the tire. The system sputters from the junction of the tire bead and rim. Two more ounces of Stan’s helps to seal the tire. However, any additional handling unsettles the system, and the sidewall begins to spit again. Adding air to the system breaks the seal, removing air breaks the seal, and I predict that low pressure riding on soft snow will certainly break the seal.
This is my first tubeless horror story.
Refinements to the system may be possible. Building up the rim with more material may create a tighter bead lock and a more reliable system, but engineering a patchwork inside of a rim to be run tubeless at low pressures in freezing temperatures is a greater risk than I am willing to accept, especially as a surefire solution is so close at hand. The full-insurance approach is the split tube method, historically referred to as “ghetto tubeless”. With a small weight gain, I know the system will seal.
Repurposing a well-loved 26″ tube from Lael’s Surly LHT, I mount the tube to the rim and cut it along the outside seam. Anyone interested in a a nicely appointed 50cm Long Haul Trucker?
It fits nicely over the rim, although a 24″ tube would be even easier to work with, and would result in a slightly lighter system.
Mount the tire and pull it into position as best as possible.
Air from a floor pump is nearly enough to seat the tire. A compressor quickly does the job, and with an extra puff of air, it snaps into place and is seated roundly onto the rim.
Before installing sealant into the system, spin the wheel to verify there aren’t any high or low spots in the tire. Now is the time to rectify any issues. Finally, trim the excess rubber. I’ve seen some people leave some of the excess tube to assist in reseating the tire in the future. In my experience, this system is so reliable that I hope not to be reseating the tire for a long time. I will, however, carry a tube as a precaution.
So far, in one week of riding, the system hasn’t lost any air, and has been reliable down to about 8psi. Past experiences with tubeless Knard tires on Marge Lite rims have also been reliable.
The 3.0″ Knard tires take on a different profile when mounted to Rabbit Hole rims. On the left, a fresh Knard is shown on a 29.1mm Stan’s Flow EX rim. On the right, the tire is mated to a Rabbit Hole, as it is intended. Not only does the tire become wider, but a flatter profile puts more knobs to the ground, and it gains a larger internal volume. On narrow rims, the bike looks and feels like a big-boned 29er. On Rabbit Holes, it is more like a lightweight fatbike. In the snow, the Rabbit Holes make a difference.
Casing diameter of Knard on Stan’s Flow EX: 70.0mm.
Outer knob diameter of Knard on Stan’s Flow EX: 75.5mm.
Casing diameter of Knard on Rabbit Hole: 75.8mm.
Outer knob diameter of Knard on Rabbit Hole: 77.1mm.
Note: These dimensions are measured on a worn 27tpi Knard, and a new 120tpi folding Knard.