Photos by Tumbleweed Bike Co.
Designing bikes for fat tires is a still an evolving science. As fat tires moved from 3.8 to more than 5 inches, the corresponding hub and bottom bracket widths are growing to accommodate all that rubber. Wider bottom brackets mean a wider Q-factor. For those who aren’t familiar with the term, Q-factor is the distance between pedals. Some riders (this author included) find the wider pedal stance of most fat bikes to be uncomfortable on longer rides—not an ideal situation for a long tour. That’s why the Prospector stands out in the fat-bike crowd: It uses a standard 73 mm bottom bracket shell.
There is more to the Prospector than a standard bottom bracket, but being able to run 26×4 inch tires with a low q-factor is pretty big news. There is also an very nice Phil Wood eccentric bottom bracket for tensioning the chain when using an internally-geared hub or single speed drivetrain. The eccentric can also be used to adjust bottom bracket height when using other tire sizes. The Prospector can fit 29×3 and 27.5×3.25 tires as well.
There are some drivetrain limitations, as there is no free lunch, even with the sweet chainstay yoke that makes this whole bike work. Fat bike tires (26×4) will only work with a singlespeed or internally-geared hubs. Single-ring drivetrains will function fine with most plus tires, but multi-ring cranks will need to be Boost offset to work.
Both front and rear wheels are 135 mm with standard quick releases, making for an easy swap if something goes wrong with a cassette body or IGH.
Here are the bullet points from Tumbleweed on the bike specs:
- Tumbleweed hollow cast BB yoke (Designed by Anna Schwinn) for maximum tire and mud clearance. Compatible with most Shimano mountain cranksets
- 73 mm Tumbleweed exclusive Phil Wood Eccentric Bottom Bracket.
- Double butted, heat treated chromoly tubing.
- Tumbleweed 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 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 inch tire with derailleurs, a 1x or offset 2x crankset must be used.
- 31.6mm seatpost, 35mm seat clamp
- Available Colors: New Mexico Turquoise and Desert Sandglow
MSRP is $1,450, but there are discounts for early orders. Bikes should ship in February. There is a “module” option as well, which will include a Rohloff Speedhub, shifter, cables/housing and disc rotor for $2,650.00
Check out the video for a full explanation of with the development of this bike.