Tumbleweed Prospector touring fat bike mountain bike

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…

Tumbleweed Prospector touring fat bike mountain bike

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.

Tumbleweed Prospector touring fat bike mountain bike

Tumbleweed Prospector touring fat bike mountain bike

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…

Tumbleweed Prospector touring fat bike mountain bike with Phil Wood eccentric bottom bracket

…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.

Tumbleweed Prospector touring fat bike mountain bike

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.

Tumbleweed Prospector touring fat bike mountain bike

Tumbleweed Prospector touring fat bike mountain bike

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.

Tumbleweed.cc

14 COMMENTS

  1. I thought the pb with fat bikes BB shell was not only the tire clearance but also the chain rubbing against the tire. with a 73 mm BB, a 9S cassette, a rear derailleur and a 4.0 tire does it still work?

    • 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 said in the article.

  2. But 26*4.0 tires are not available anywhere either. And this bike is not going to fit the 1.75-2″ tires that I typically see in Latin America.

    • Lots of MTBs will do if that’s a real concern. For someone wanting to tour on these newer tyre formats there’s not many places fed-ex etc can’t deliver to and most tyre failures can be bodged to get you to a place where you can wait for a new tyre. Pros and cons etc.

    • That depends on the width of the fatbike rim used. On a 100mm wide rim, sure, not likely. But I don’t see why a 65mm or 80mm isn’t doable to get you to the next town to pick up the 4″ you’ve ordered from the internet with next day delivery.

      The bottom bracket height might be a bit interesting but then you can fiddle with that on this bike. A low BB height might be desirable even if you have some tarmac to cover on 2″ slicks.

  3. Pretty neat project – certainly a bike that has a lot of versatility. One thing the article doesn’t mention is Daniel Molloy’s relationship with Grant Peterson (highlighted on the Tumbleweed website). Huge compliments from Grant on Daniel’s design. If you’re going to learn about versatile, durable steel bikes, Grant’s probably the guy to learn from.

    Kudos on the bike – I’m excited to see the production version out int he wild.

  4. Looks like 2 bolts pinch the eccentric BB in place. I wonder why a clamping design was not chosen. A BB insert clamped inside the shell will never creak or work loose.

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