For backcountry touring bikes, things like 29+ make a lot of sense for their comfort and excellent roll over characteristics. The catch, as several tourers have explained, is parts availability. Twenty niner tires weren’t all that common even a couple years ago, and in more remote parts of the world, 26″ is still the de facto standard.
The way around it? Make a touring mountain bike that can handle any wheel size by building it around a 26×4.0 fat bike tire, of course. And should you want to run a 27.5×3.25 or 29×3.0? Go for it. But this versatility presents a new concern…crank set compatibility. The wider fat bike spindles are probably even less common throughout the world than a fat tire, so the new Tumbleweed Prospector built big tire clearance with a standard 73mm bottom bracket shell and narrow Q-factor…
The Prospector comes equipped with a maintenance free Rohloff internally geared 14-speed hub, but is compatible with front and rear derailleurs, too. The double butted chromoly frame gets rack and fender mounts, three downtube water bottle bolts for options when it comes to placement, and a rigid steel fork.
The fork shares the rear end’s 135mm axle spacing, making front and rear wheels interchangeable if you build up the front with a rear hub, too…perhaps a single speed hub as a backup.
The secret to their combination of big tires and narrow BB shell is a custom investment cast chainstay yoke. It was designed by none other than Anna Schwinn (full disclosure, Anna writes for Bikerumor but had no input on this article). That allows for a standard crankset and crank arms, which are tucked into…
…a Phil Wood eccentric bottom bracket. It provides the ability to keep chain tension on the Rohloff system without using a sliding or swinging dropout. It also lets you adjust BB height slightly.
Those 135mm hubs should be easier to find in foreign lands, too. The frame design creates room for front gearing up to 24/38 (double) or 24/32/42 (triple) with the EBB set in the rear-most position. Bigger gears can be used if the EBB is set toward the front. If you’re running a 3.0 tire or larger and want to use a rear derailleur, you’ll need to have a 1x chainring up front or offset (think “Boost”) double to ensure the chain clears the tire when at the top of the cassette.
As a bullet point list, specs are:
- Tumbleweed’s cast BB yoke (Designed by Anna Schwinn) for maximum tire and mud clearance. Compatible with most Shimano mountain cranksets
- 73mm Tumbleweed’s exclusive Phil Wood Eccentric Bottom Bracket.
- Double butted, heat treated chromoly tubing.
- Tumbleweed’s vertical dropouts (Designed by Anna Schwinn) with Rohloff OEM slot and chainstay mounted disc brake. M6 and M5 Rack and Fender mounts. Replaceable derailleur hanger (Wheels Manufacturing number 6)
- Braze ons: Front and rear rack and fender mounts, three water bottle mounts on frame, triple water bottle mounts on fork
- 135mm symmetrical QR rear hub spacing
- 135mm fork spacing for rear disc spaced hubs, allows front and rear wheel interchangeability. Unicrown, 100mm suspension corrected
- Tire clearance for 26×4″ on 65mm rim (Rohloff SPEEDHUB or singlespeed only), 29×3.0″ on 50mm rim, or 27.5×3.25″ on 50mm rim
- Chainring clearance: 24-38 Mountain Double, or 24-32-42 Mountain Triple. Chainring clearance is only limited when the Eccentric BB is in the far rearward position. Larger chainring combinations may be used if this rear position is avoided. In order to use a 3″ tire with derailleurs, a 1x or offset 2x crankset must be used.
- 31.6mm seatpost, 35mm seat clamp
The frameset with fork and hardware is $1,450. Grab a frame module with the Rohloff Speedhub, shifters, cables and rear disc brake rotor for $2,650. The complete bikes start at $4,000. Delivery is expected around February 2017. Pre-order now and you’ll get $150 off full retail.